THE BRITISH AMATEU R

•T
TELEVISION CLUB .

FEB 1973
 1

THE BRITIS H
AMATEU R
TELEVISION CLU B
Committee Members and Club Officer s

PRESIDEN T MAILING LIS T Nicholas Salmon

R .S . Roberts G6NR Lewis Elmer G6AGU/T " Cobbolds "
6 Atterbury Close , Magdalen Laver ,
CHAIRMAN West Haddon , Nr . Ongar ,
Malcolm Sparrow G6KQJ/ T Rugby , Essex CM50E E
64 Showell Lane , Warwickshire . Tel . Moreton 30 9
Penn, Wolverhampton , Tel, West Haddon 32 4
Staffordshire . James Cunningham
Tel, Wombourne 503 7 EQUIPMENT REGISTRY 3 Ramsden Road ,
Alan Watson London ,
GENERAL SECRETARY "Somerby View " N11 3JE .
Joe J . Rose GESTO/T Bigby ,
Pinchbeck Farmhouse , Barnetby ,
Mill Lane , Lincolnshire .
Sturton-by-Stow , Tel . Searby 28 7
Lincolnshire .
Tel . Stow 35 6
C Q - T V is pub-
MEMBERSHIP SECRETARY lished quarterly by the
Gordon Sharp ley G6LEE/T British Amateur Televi-
52 Ullswater Road , sion Club and is poste d
Flixton , Cyril Chiver s free to all members .
Urms ton , Mbrtimer Street , Single copies are avail -
Lancashire . Trowbridge , able from the Editor a t
Tel . Urmston 803 1 Wiltshire . 25p each ; back numbers
Tel . Trowbridge 2848 are also available t o
TREASURER members at reduced pri-
Alan Prat t Dave Lawton G6ABE/T ces .
10 Grammar School Road , 79 Kingsland Road ,
Brigg , Boxmoor , Overseas member s
Lincolnshire . Hemel Hempstead , may have their copy of
Tel . Brigg 301 4 Hertfordshire . C Q - T V sent by air-
Tel . Hemel Hempstea d mail, for a surcharg e
EDITOR C Q, - TV 50516 . depending on their coun-
Andrew Hughe s try . Details are avail-
93 Fleetside , John Lawrence G6JGA/ T able from the Treasurer .
West Molesey , 40 Aberconway Road ,
Surrey KT8 ON Q Prestatyn , Members wishing t o
Tel . 01-979 998 3 Flintshire . have material publishe d
Tel . Prestatyn 325 5 in C Q - T V should send
SALES & LIBRAR Y the manuscript and draw-
Grant Dixon G6AEC/ T ings to the Editor ; art-
"Kyrles Cross " Nigel Walker G6ADK/T icles are invited on al l
Peters tow , 1 Eva Road , subjects of interest t o
Ross-on-Wye , Gillingham , amateurs and should b e
Herefordshire . Kent . of about 1500 words ;
Tel . Ross-on-Wye 2715 larger articles should
be divided into conven-
ient Parts for public-
COVER PHOTO Oscar 6 SSTV Picture s ation in consecutive
issues of the journal .
 2

EDITORIAL CONTENT S

As a result of the last committe e Committee Member's Addresses page 1

meeting there is a slight change to th e Editorial page 2

list of Club Officials in that Gordo n Circuit Notebook No . 12 page 3
Sharpley takes over the post of Membershi p
European Reporting System page 6
Secretary from Nick Salmon, who has stoo d
down after a long and hard-working spel l Ideas for Amateur Colour Part 5 page 7
in the post . Malcolm Sparrow remain s 1972 atv Contest Results page 1 0
Chairman and sends this message to members :
Receiving Amateur tv page 1 1

Slow Scan News page 1 4

Dear Members ,
A Slow Scan Scanner page 1 7
The first meeting of the new B .A .T .C .
Integrated Circuits Part 11 page 21
Committee elected at the September Genera l
Meeting of the Club was held at Wolverhamp- Postbag page 31
ton on December 10th last .
Adverts page 3 2
At the meeting I was elected to serv e
as your Chairman for the next two years an d
I would like to draw your attention to th e tuner and get co-channel interference? I n
new list of Club Officers which appears i n all a narrower atv band on 70cm should lea d
this issue of C Q - T V In addition t o to improyements in operating techniques too .
welcoming those new members to our committe e With more stations becoming active and at v
I must also voice a sincere vote of thanks contests being organised, it is up to us t o
to those retiring committee members who hav e match the problems with new methods .
now stood down and thank them for thei r As amateurs we experiment in the ar t
support and efforts during their term o f of communication and yet, being honest wit h
office . ourselves, we do not seem to communicat e
Looking forward, the future holds a with each other very well . For a start ,
challenge to us all with a smaller 70c m make a New Resolution for 1973 to let other s
frequency allocation in the U .K . for ama- know of your progress and problems . No doub t
teur vision of 432 - 440MHz, which we i n others have had the same problem and may hav e
turn have to share with the sound amateur s found the answer . To this end use C Q - T V .
in 432 - 433 .5MHz and the amateur satellit e Air your views and news - it is your maga -
signals around 435MHz . zine so you should use it .

On the brighter side by negotiatio n We hold a General Meeting of the Club

with the R .S .G .B . the 70cm beacon station s every other year and each time we usually tr y
are shortly to be moved to around 432MHz t o to suit the majority of our members by hold-
minimise interference with amateur tv . In ing it in London . I know that for some of our
all we should perhaps look to our own equip- British members this is too far to travel ,
ment and try to improve our atv receptio n so why not organise your own mini-Convention .
techniques - why use a wide open front end continued on page 16
 3

CIRCUIT J . Lawrence GWEJGA' T

NOTEBOOK No1 2

Camera Tube Scanning Circuit s The basic circuit is shown in Fig . 1a .

The primary requirement of the lin e The transistor is used as a switch with th e
or field scan deflection circuit is tha t line scan coils in the collector circuit .
it should provide a linear scan and rapi d To start with, let us assume that th e
retrace or flyback . base of the transistor is reverse biasse d
As the scanning is done magnetically , and that the collector is at the suppl y
this means a linearly changing current dur - voltage . At the start of the line scan th e
ing the scan and a rapidly changing curren t transistor is switched on hard by a suitabl y
during the flyback .
Transistor Line Scan Circuit s
(a) 0
Most simple transistor line scan cir-
U H
cuits rely on the linear rise of curren t
that occur in an inductance (the line scan capacitance
coils) when a voltage step is applied acros s free conditio n
it .
ringing caused
(b) 01 f by C 7
%.1

(c) I I
0
line scan
I
fly back ff back

Fig . la Fig . l b
 4

—'Obb\

mini oN= A1F

+0 I

bbb

Ur

C C +0 ~

J
my ~~ N

`rlllTV V VV'—,

uo

_ L
NO O 0 O
Nm
¢ O

W UUO
Q
 5

large positive current applied to the base . of current causes the scanning coils, i n
The collector falls immediately to almos t parallel with C7 the flyback capacitor, t o
zero volts and the scan coil has a voltag e oscillate at their natural resonant freque-
step almost equal to the supply voltag e ncy, shown dotted in Fig . lb . However, D 2
across it . will not allow the collector to swing nega-
tive and as soon as the negative half-cycl e
Thecurrent through the coil build s
of the natural oscillation commences D 2
up in a linear manner giving a substantiall y
conducts, driving current through the scann-
linear deflection . At the end of the line
ing coils and starting off the next scan .
scan the transistor is switched off agai n
by reverse biassing the base and the coll- D2 is forward biassed by the potential
ector once more becomes an open circuit . divider R14 and HIS to ensure a smooth cha-
This causes the current and magnetic field nge over from reclaimed scanning current t o
in the coils to collapse producing a rapi d current provided by the line output transis-
deflection in the opposite direction an d tor Tr5 .
generating a reverse voltage having a high An additional choke L2 is provided t o
peak value as shown in Fig . lb . enable shift currents to be passed throug h
the scan coils for picture centring . The
A complete practical circuit of a lin e SHIFT control is RV3 .
scan generator is shown in Fig . 2 . In thi s
Scan amplitude is determined by th e
circuit the line oscillator consists o f
voltage applied to the output stage and
Tr1, Tr2 and Tr3 connected to form an as -
this is adjustable by RV2 the WIDTH control .
table multivibrator . This is synchronise d
at line frequency by negative going lin e With a 12Volt supply rail and norma l
drive or blanking pulses applied to Cl . Em- direct drive transistor type scan coils ,
itter follower Tr3 is included to ensur e this circuit, which is based on the Lin k

good waveshape at C5 . The line frequenc y 101 Camera, will provide more than adequat e

is set by RV1 . scan for a Vidicon tube with integral or

separate mesh .
The driver stage Tr4 is turned of f
during the line period and on during th e References Millman and Taub
flyback, this results in Tr5 the line out - " Pulse Digital and Switching Wave -
put transistor being switched hard on dur- forms" Page 57 2
ing the line scan period and cut off durin g McGraw Hil l
the flyback . Instruction Manual for the EM I

As previously mentioned, the curren t type 8 Camer a

in the coils rises linearly during the sca n Instruction Manual for the Link
until Tr5 is cut off again at the end of th e 101 Camera
line . In the practical circuit the coil s
are a .c . coupled to Tr5 collector by C90 an d
Cif and the d .c . feed to the collector i s
via a choke L1 . This removes the d .c . com-
ponent from the coils and allows symmetrica l
deflection .

During the flyback the sudden collapse

 6

European Amateu r
tv Reporting Syste m
Picture Carrie r

BO Nothing receivable from the picture carrier .

B1 A3 sound or speech audible, receiver on AM .
B2 A3 sound visible, speech understandable .
B3 Non-lockable picture visible, A5 rumble available .
B4 Lines can be locked, A5 rumble loud .
B5 Lines and picture can be locked .
B6 Call readable .
B7 Persons recognisable .
B8 Details recognisable .
B9 Picture almost free from noise .
B9+ Picture completely free from noise .
N .B . The tv receiver is switched to AM for B1 - B 4

Sound Carrie r

TO Nothing receivable from the sound carrier .

T1 Test tones audible, speech unintelligible .
T2 Speech sometimes understandable .
T3 Speech understandable when picture is at black level .
T4 Speech understandable when picture contest is white .
T5 Speech understandable if tuned for best sound .
T6 Poor speech understanding if tuned for best picture .
T7 Good speech understanding if tuned for best picture .
T8 Sound almost free of distortions if tuned for best picture .
T9 Sound completely free of distortions if tuned for best picture .

Remark s

BI The tv receiver is switched to AM . The vision carrier is to be modulated by speech in th e

A3 mode .
B2 Again the tv receiver should be switched to AM . Horizontal bars should appear on the screen
if the sound is tone of 200 - 800 Hz . Whistling into the microphone is an alternative .
B3 Sync pulses should be visible if the brightness is turned up .

B4,5 It should be possible to lock both frame and line by careful adjustment .
B6 The call sign should fill the screen, and it may be necessary to darken the shack to read it .
B7 The picture should be of a well known person, such as the Queen or some local personality .
B8 Scales, and the hands of, watches should be discernible .
B9 3MHz on 625 should be resolved .
B9+ 400 v should be available from the aerial .
 7

Ideas for Amateu r

a rt 5
Colou r
Nigel Walke r
GBADKT

The amateur who has managed to produc e only, to lowlights, and not lowlights plu s
colour captions by simply feeding the out - highlights as would otherwise be the case .
put of a monochrome camera into the R,G or B Output "C " , also inhibited by blanking ,
input of a coder or a monitor will fee l produces an output when " A " or " B " are i n
that the next step should be to build a a low state and thus produces a signa l
prover " synthesiser " , where the artific- corresponding to the blacks, or backgroun d
ially produced colours are infinitel y of the picture .
variable . Figure 2 shows the output stages . The
The synthesiser to be described split s nine potentiometers provide independen t
the video input (from the monochrom e adjustment of the proportions of red, gree n
source) into three levels, such that a or blue for each of the three levels, an d
different colour can be set up for eac h are the controls which should be mounted o n
level . A total of nine potentiometer s a front panel . The output filters are pro-
are thus required to control the colou r vided to limit the frequency spectrum o f
output . the outputs to that corresponding to th e
625 line system bandwidth .
Figure 1 shows the actual level split-
ter . The video is first clamped, and the n With careful use of crayons applied t o
fed into two level detectors, the switch- a caption made with white " Letraset " t o
ing level of which is made variable by produce three brightness levels (i .e . black ,
means of preset potentiometers . The out- grey and white) quite reasonable thre e
puts from the two level detectors are the n colour captions can be produced using thi s
fed to a gating system ; for output "A " synthesiser . Very colourful effects ca n
(highlights) the signal is inhibited b y also be produced by pointing the camera
blanking, but is otherwise unaffected . at an ordinary scene, and there is muc h
Output " B " (lowlights) is inhibited b y scope for artistic experiments alon g
blanking too, but it is also inhibited b y these lines .
"A " thus producing a signal corresponding
 8

----
 9

c
 10

1972 atv contes t

results .
B .A .T .C . N A T I O N A L C 0 N T E S T 23 -24 -30 SEPT, 1 OCT . 197 2

SECTION ON E

PLACE CALL POINTS No . of CONTACTS BEST DX No . STATIONS CALLED/WORKED

1 G6AEV/T Portable 4294 58 G6AFW/T 165Km 12 - 8

2 G6AGT/T/A 3309 54 G6AEV/T 135Km 5 - 18

3 G6AFW/T 3102 31 G8ARM 225Km 11 - 8
4 G6KQJ/T 1450 18 G8ARM 203Km 6 - 9

5 G6GDR/T 679 13 G60P3/T 46Km 4- 3

SECTION TW O
1 G3YQC 712 6 G6AGT/T 68Km 2 - 0

Some twenty one /T stations took part altogether, with thirty one sound only stations .
Conditions for the first weekend were above average, which added to the normal range expecte d
for atv .

It is a pity that so few stations submitted an entry, and it is hoped that more will d o
so with the atv cumulative contest now being held . Please note one omission from the publishe d
rules, in that there will be two sections to the cumulative contest : -
A. For those stations transmitting at v
B. For all others .

The results of the September contest have been forwarded to our German friends, and w e
await the results of the International Contest with interest .
 11

Receiving Amateur tv for the Beginne r

Using the Mullard ECL1O43 Varicap Diode Tuner .

by Malcolm Sparro w

To receive Amateur Television these days need not be as hard as it used to be in the ver y
early days when A .T .V . had just started ; in fact, using the new Mullard ECL 1043 tuner uni t
makes it just about as easy as possible .

The one saying to remember when trying to receive any UIL' signals is that "A chain is only
as strong as the weakest link in it " . In ether words, provided that there is an ATV signa l
on the air, to receive it one requires : A 70cm aerial, a coaxial cable to connect it to th e
tuner unit, a tuner unit, and a tv receiver . If any of the items does not function properly
then the results will be impaired .

FIRSTLY THE 70CM AERIA L

These days it is rarely worth trying to design and construct your own aerial . J . Bea m
Engineering Ltd . of Northampton produce a range of 70cm aerials and the beginner would be wel l
advised to start off by purchasing one of their aerials such as the 18 element parabeam (Cat .
No . 70/18P,) price £7 .45p, which has a gain of 17dB over a plain dipole . (Do not use thei r
14 element skybeam aerial for ATV as this aerial does not have a suitable band width for ATV .

Whichever aerial you finally decide upon, the next thing to consider is where to put it .
In practice it will pay to try to mount the aerial so that it is clear of all the roof-to p
obstructions as wet tiles can make quite considerable signal attenuation at 70cm . Also som e
provision for turning the aerial should be made to enable an incomming signal to be peaked fo r
maximum . This may not coincide with the most direct route to the transmission source .

2tEXT . THE AERIAL COAXIAL DOWNLEA D

Having decided upon which aerial to use and where and how you are going to mount it th e
next thing to consider is the coaxial downlead .

This should be as good a cable as you can obtain and afford . There is no point in erecting
a high gain aerial only to loose all the signal before it gets to the tuner unit . One shoul d
use a good quality low loss BBC 2 type coaxial cable such as " Aerialite Type M4205 Aeraxia l
Cable " . This is a e inch diameter coaxial with a cartwheel cross-section . That is, the in-
sulator between the inner and outer cables is partially air-spaced . A point often overlooke d
when using this type of semi-airspaced coaxial cable is that although the air in these hole s
in the cable is dry when you purchase the cable new, it will soon become damp when connecte d
to the aerial way up in the air .
 12

Whilst the cable will give first-class results when .first connected to the aerial it wil l
soon deteriorate in performance if steps are not taken to trap the dry air inside the cable .
This is simply acheived by cutting the cable to the required length to be used - always kee p
it as short as practical and do not leave large lengths in use just to avoid cutting a run o f
coaxial cable - and then by melting the insulator at each end of the cable, seal each end t o
keep the dry air in the cable before attaching it to the aerial . This can usually be don e
quite easily by using a dry soldering iron, but take care not to let the inner and oute r
cables short out whilst doing this .

NOW TO THE TUNER UNI T

The Mullard Varicap Diode Tuner Unit type ELC 1043 is available from Manor Supplies Ltd . ,
at £4 .50p each plus 25p post & packing . This tuner is built in a tinplate box with detachabl e
sides and is tuned by varying the voltage applied to the Varicap diode in it ; it should b e
connected up as follows :

The aerial lead should be connected to the input terminal which is on one end of the unit ,
the outer of the coaxial cable being soldered to the tuner chassis .

Next, refer to the pins and holes which are located in the base of the tuner unit betwee n
the four mounting lugs . Commencing from the end of the tuner which has the aerial input ter-
minal on it number these holes (some of which have pins in them) 1 to 11 and connect them u p
as follows :

• +I 2 v

IK PRESET IOK IK LIN

0-I 2 v
AP

-~ O
Pl 2 PIR4 P~V8 PIN 5
Purer chassis A .G .C . r .f . osc/mixer TUN E
Transistor Supplies .

The lKohm linear Variable potentiometer feeding pin 5 is the tuning control, whilst the
1K preset control should be set to feed pin 2 with 3v +ve to the tuner chassis . The outpu t
from the tuner is taken from pin 10 with the braid of the output coaxial cable being connecte d
to the tuner chassis .

The output lead should be taken to the aerial input socket of the tv receiver and th e
receiver set to channel one . With the tv set turned on and 12v dc . applied to the tuner (an d
the aerial connected to the tuner), you are now all set to watch for ATV pictures provide d
that there are some on the air to start with, of course .

Once a signal has been received the I .F . output coil slug in the tuner can be tuned for th e
best signal but there will probably be only a slight improvement .
 13

This equipment will provide an up-to-date ATV receiving system which will be on a par with
any valve tuner plus low noise transistor preamplifier, as the Mullard Tuner noise factor i s
quoted as being 8dB .

It will of course be necessary to change over the detector diode polarity in the tv se t
and also the link time base frequency if you wish to watch 625 line -ve modulation ATV as th e
system as described is intended for 405 line +ve modulation ATV as mainly used by amatuer s
outside the London area .

Finally, do not put more plugs and sockets in your 70cm aerial down lead than absolutel y
necessary, as each time you use one you will lose a little of the signal .

NOTE : If you want to tune the whole of the television band IV with your tuner it will b e
necessary to arrange for the timing voltage on pin 5 of the tuner to be varied between 0 .3v
and 28v +ve, but the circuit as shown should tune the amateur 70cm band without any need fo r
internal modification to the Mullard Tuner unit .

References : J . Beam Engineering Ltd . ,

Rothersthorpe Crescent ,
Northampton .

Manor Supplies Ltd . ,

172 West End Lane, London, N .W . 6 .
Mail order 64 Golders Manor Drive, London, N .W . 11 .

Data Sheet on UHF television tuner type ELC 104 3

Mullard Ltd . ,
Mullard House ,
Torrington Place ,
London, WCIE 7H D

THE C - T V S . 0 .0 . locking power are improved too . One sligh t

At the time of going to press 99 spg board s problem is that it seems to make the vert-
have been sold to B .A .T .C . members - toge- icals rather kinked, There is no effect o n
ther with 47 Genlock boards, Who is goin g the Genlocking performance .
to be the lucky fellow to get number 100 ?
This represents about 10% of B .A .T .C . mem-
bership .
In reply to a mainslock modification as sugg- "SLOW SCAN TELEVISION "
ested by david Wilkinson on page 32 of thi s Some members who have bought this bookle t
issue ; this has been tried and found to work , unfortunately did mot receive an errata slip ,
It is not the complete answer though . Th e Please note that in Figure 10 on page 6, th e
50Hz phase modulation is reduced from abou t base of the BFX29 should be connected to th e
11us to about 8us but the pull in speed and collector of the BFX85 and NOT to the emitter .
 14

Slow Scan New s

Dear Fellow Slow Scanner,

As you probably know Oscar 6 is now in orbit and several of us hav e
had success in sending slow scan television through the satellite . On early evening passe s
we occasionally hear "G" signals on sideband and CW . We would very much like to work a slo w
scan contact with a DX station .

If you are interested please drop me a line immediately . I suggest if you are intereste d
that you sked me on 11 .30GMT on Wednesdays on 1423OKc/s and we can arrange for a contact throug h
the satellite . Oscar 6 is turned on on Thursday, Fridays, Saturday and Sunday evenings as wel l
as Saturday and Sunday mornings . This saves on battery power since one of the solar panel s
is having trouble . If you skeded me on Wednesday we would be ready for weekend passes . Another
way to alert us is to contact the slow scan television net which meets at 1800GMT on 1423OKc/ s
each Saturday afternoon . I am one of the net controllers and can always be reached directl y
or by relay from the Atlantic coast at that time .

Tne procedure for making contacts is to broadcast continually on your chosen frequenc y
for the full 20 minutes of the pass and to check later to see if you were seen or heard . The
early pass of the evening is the only one of that group where we have a chance of seeing eac h
other across the Atlantic . WA9UHV and myself are operating on 145 .930 and 145 .940 respectively .
This brings us out at 29 .480 and 29 .490MHz respectively . If you can sked me I can alert yo u
to the possible passes where we might have success .

Please let me hear from you . Satellite communications are a great deal of fun and ar e
very exciting .

Don C . Miller ,
Waldron, Indiana ,
Box 95, 46182 ,
U .S .A .

OSCAR6

Oscar 6 was launched on 15th October 1972 from Vandenburg, California, piggy-back fashio n
with a weather satellite . The Oscar translator was designed and built by the AMSAT organisation ,
a group of radio amateurs dedicated to forwarding the technology of Radio Communications .

The translator has an input band around 145 .5 and an output band from 29 .45 to 29 .55MHz .
All modes of radio communication can be translated .

The orbit of the satellite is polar with an inclination of 101 .73 degrees and a period o f
114 .5 minutes . There is a telemetry beacon on 29 .45MHz . The "CODESTORE" memory of Oscar 6 i s
capable of being loaded with ground based information while in orbit . WIAW, the official
 15

American Radio Relay League station, constantly transmits undating information to all intereste d
radio amateurs on the QST published frequencies . Announcements are made in both ' phone an d
RTTY .

The photos show W9NTPs gear which made the first two way QSO through Oscar 6 . The firs t
contact was made on orbits 30 and 41 and by October 40 pictures had been exchanged wit h
WA9UHV . The gear at W9NTP comprises a HeathSB101 high frequency transceiver with 30w out, a
homebrew linear 100w 2m amplifier with a 4CX250 in the final, a 10 element vertically polarise d
2m antenna, rotable in azimuth only, a 10m 4 element rotable Yagi, a NX-303 National Hamban d
receiver on 10m and a homebrew sampling SSTV camera with 7 inch monitor . Similar equipment i s
used at WA9UHV except that the aerials are notable in azimuth and elevation .

' 9NTP reports that QSB is so severe that it is difficult to get even one complete SST V
frame . The main problem seems to be "power robbing" by other stations, but as can be seen by
the photos (see this page and the front cover), some success has been possible .

ROBOT EQUIPMENT (especially Camera Model 80 )

Richard Thurlow, G3WW, of Wimblington, Cambridgshire has sent us some information about a ne w
specification for SSTV, as used by the M .P .T ., resulting from some considerable correspondenc e
over the last few months . This is how G3WW tells the story .

"To those of you who I have pestered for information by phone calls, cablegram and letter s
as to why and how the ROBOT camera with its 128 lines is allowed to be used universally in bot h
the 60Hz and 50Hz AC Mains areas of 120 lines standard, I hasten to report that after passin g
on to London the excellent information gathered, especially from K6IV himself, W4BW the Chie f
of the Amatuer and Citizens Division of the FCC . thro my good Attorney friend of 1960 Washingto n
DC visit W3GZ/4, and KIPLP Asst . Tech Ed . QST who reviewed the ROBOT equipment, that in the US A
the 120 line standard is one adapted by the US Amateurs and is not regulated by the FCC, and tha t
ROBOT have departed from the accepted standards in two respects on the grounds that the perform-
ance is improved and the signal from the camera is received well by all monitors i .e . 128 line s
per picture and Vertical sync pulse duration 66 milliseconds rather than 30 milliseconds, I have
 16

today received permission from the Ministry of Posts and Telecommunications (per Mrs . A .I .
Campbell) to use SSTV under fresh conditions .

our engineers have now reviewed the technological aspects of the equipment required t o
meet our specifications and I have pleasure in advising you that we are prepared to grant yo u
permission to use the following bands : 7-7 .10MHz, 14-14 .35MHz, 21-21 .45MHz, 28-29 .7MHz ,
144-146 .OMHz two year period etc . P .S . Enclosed is a copy of our revised specification whic h
covers ROBOT 80 ' .
SLOW SCAN TELEVISION SPECIFICATION

Number of lines per frame 128 ± 8 line s

Aspect ratio 1 : 1
Horizontal frequency (frame) 163 ± 1H z
Vertical frequency 7 .68 secs . (limits 6 .79 to 8 .68 secs . )
Horizontal sync pulse 5 millisecond s
Vertical sync pulse 30 milliseconds (nominally )
F .M . subcarrier sync 1200H z
black 1500H z
white 2300H z
Those of you who were NOT pestered might like to know that the necessity for all the abov e
arose from the fact that when applying to transmit SSTV I (and as later discovered G3NMH, also )
sent up with my application ROBOT ' s printed brochure packed with their Model 70 Monitor WHIC H
SETS OUT THEIR SPECIFICATIONS FOR USE WITH USA 60Hz AC Mains ONLY ; permission could not b e
granted ON THESE FIGURES ; ability to perform on 50Hz AC Mains quickly explained by provision o f
'a changeable jumper ' in the ROBOT Camera, but there remained the 128 lines against the worl d
wide adopted 120 lines .

Get some ideas from other members in you r address is on page 1, and this time we hav e
area (the Treasurer will tell you who the y a little extra to ask of you . To enable
are) and we will try to get at least on e us to bring our records up to date, if yo u
Committee member to attend to bring you up have a Postcode, could you let us kno w
to date . Just give us a reasonable amoun t what it is . Also, if the address on the
of notice ; remember it takes approximatel y envelope you received this C Q - T V in i s
ten weeks to get a letter into print i n wrong in any way, please let us know abou t
C Q - T V. that too . This will help us, the Post Office ,
and ultimately, yourselves .
Finally may I wish you all you wis h
yourselves for 1973 and here ' s to a mor e At the next vhf Convention, to be hel d
successful, and dare I say, colourful at v as usual at Whitton, B .A .T .C . would like t o
year to all our members and let us al l have an organised display, if at all possible .
remember to try to communicate . Dave Lawton G6ABE/T has taken on the resp-
Malcolm Sparrow G6KQJ/T onsibility for coordinating the effort, s o
Hon . Chairman B .A .T .C . if you will be there and would like to help ,

Once again subscriptions are due - or have some equipment you would like t o

it is only one pound, after all . And thos e show, please contact Dave - his address i s
who don ' t pay, won ' t receive C Q - T V . printed on page 1 .

Please send to the Hon Treasurer, whose THE EDITOR .

 17

A Flying Spot SST V

Scanne r
B . J . Arnold M .A . G3RHI

This article concentrates on the electronics of the scanner rather than the optics . I t
has been used at 03RHI without an optical system to make tape recordings for transmission b y
placing cutouts directly on the face of the station SSTV monitor tube . The contrast contro l
on the monitor is turned right down and the monitor raster is synchronised from the sync puls e
generator in the scanner . Thin card cut-outs or transparent acetate with black letraset letter s
are placed firmly on the tube and the 931A is stood about 12 inches away . Care is taken t o
minimise light leakage between the card or acetate and tube but provided this care is take n
god black and white captions and simple cartoons are recorded . An optical system using 35m m
transparencies would be a real improvement but so far the search for readily available part s
for an easily built lens and transparency changeover system has not been successful . By con-
trast all the parts for the electronics are readily obtained .

The power supply is conventional . The Crofton Electronics transformer, though not essen-
tial, might well have been designed for the job . The 12 volt supply is standard . The 5 vol t
regulator was placed on the modulator printed circuit board and wired in permanently to mini-
mise the risk of connecting 12 volts to the I .C .s . The photomultiplier EHT is a standard ful l
wave voltage doubler connected to the 200+ volt HT winding on the Crofton transformer . Th e
load is a modest 1mA but safety precautions should be taken since with this transformer th e
EHT voltage is some 480 - 500 volts .

This is enough for the 931A . Higher EHT can be used so long as the total voltage is mea-
sured and the resistor connected between X and the EHT calculated so that the total curren t
through the chain is 1mA using the values in Figure 2 . With EHT connected the tube should no t
be fully exposed to daylight or bright light . One of the old 14 inch coil forms or a piece o f
plastic tube with 3 strips of foam draught excluder inside make a good shroud . The outpu t
voltage of the tube is negative and a positive voltage is needed to drive the modulator . Th e
2N3819 buffer also conveniently inverts the signal polarity and its 2Mohm input control shoul d
be readily adjustable . Screened cable is used between the FET and point B on the modulator .

The modulator circuit includes a sync pulse generator .T7and T8 square the 50Hz voltag e
which is divided in IC3 by 3 and shaped by IC2 to provide line sync . IC4 and 5 together divid e
by 120 to give frame sync shaped by ICI . The heart of the modulator is the multivibrato r
around T3 and T4 . A ganged pot is not available for P3 and P4 but the adjustment of separate
18
 19

pots in step is easily done . T5 is a buffer and a square wave is present at the collector whic h
is followed by a low pass filter . The result is a sine wave at the base of T6 which is an amp-
lifier to make up for the losses in the filter . On receipt of a sync pulse T3 and T4 must pro -
duce 1200Hz, and black 1500Hz and on white 2300Hz . T1 and T2 provide the means of varyin g
voltages to control this frequency . To set up the modulator a frequency counter is essential .
For initial adjustment the 2N3819 is disconnected from point B and the SPG is disconnected fro m
point A . The black pot P1 is then adjusted to give an output of 1500Hz . Point TP is then ear-
thed and the sync pot P2 adjusted to give 1200Hz . The FET output is then connected to poin t
B with the 931A covered to simulate black . P1 is readjusted since the frequency will rise a
few cycles in response to the 0 .5 volt or so always present at the FET output . The tube is the n
exposed to a bright continuous raster in a dark room and the 2M pot adjusted to give 10 volt s
at point B . The CRT brightness control is set at a sensible working level without any colou r
filter . P3 and P4 are then adjusted to give 2300Hz . Thus the multivibrator cannot go abov e
this frequency since the maximum voltage is controlled by the 10K resistor connected to th e
12 volt supply and thereby determining the FET operating point . The black and sync frequencie s
are then rechecked by the original procedure since adjustments are to some extend interdependant .
When completed the SPG is reconnected to point A . Prior to this the SPG outputs can be checke d
on a scope for voltage and length of pulses . Even with the so-called new but cheap I .C .s ther e
should be some 2 volts at point A and only 0 .6 volts is needed at the base of T1 . T1 is a
transistor switch which on receipt of a sync pulse bottoms its collector to achieve the sam e
effect as earthing TP during the setting up procedure . Throughout all adjustments a smal l
speaker connected to the transformer wads it and gives a good indication of success or lack o f
it . The unit is now ready for operation . The Mark I version was built on an open chassis whil e
Mark 2 was built in a diecast box with a rectangle cutout to expose the sensitive area of th e
931A .
Lucky the operator who has two monitors or a monitor and a separate CRT unit producing a
raster . With the raster set up in the dark about 12 inches away from the 931A and synchronise d
from the modulator a facsimile of the card cut-out or transparency placed on the face of th e
tube can be seen on the monitor to which the modulator is connected . If a second monitor i s
not available patience is necessary while the picture is tape recorded and then played back o n

See text
 20

the monitor originally used to provide the raster . Although time consuming, with experienc e
results are good since the only two variables are the CRT brightness control and FET input . I n
practice the FET is set and the brightness is varied . Operation is best done in the dark s o
tape recording rather than direct transmission is more convenient .

FOOTNOTE : The author has a few printed circuit boards for the combined SPG and modulato r
priced £1 .60 . P1,2,3 and 4 are available fitted to this board at 40p the set . The 931A and
base are stocked be Henry ' s Radio .

16v
+ A B

Bridge
C
1 10p F

T1
VR_ RS components MVR 1 2

Bridge RS components REC60

T1,availab:e from Crofton Electronics _same as Camera Kit Transforme r

Fig .3. Power suppl y

NEWSF LASH

A TV Convention is to be organised in 1973 to take place in Germany . B .A .T .C . members who ar e

interested in attending this Convention should contact the organiser Manfred May DC6EU ,
Caesarstrasse 13, Bayenthal 51, D5000 Koln, Germany for details .
 21

INTEGRATES PART 11

CIRCUITS
A.CRITCHLEY Dip El; C Eng ; MIERE .

MORE ON OPERATIONAL AMPLIFIERS

However, In is so small as to be negligible in any but the

FRfiltoCY CCtTRNSATLON
worst Op . Amps .

This is a complex subject which tends to frighte n Thus I i + I f = 0 or I i -If

people off Op . Amps . You may feel the same after thi s
description - in some detail to show the reasons fo r Also, vo = -vn .A or vn =
v c/A
the various methods of compensation .
The basic reason for frequency compensation of high -
For a normal low-frequency amplifier it is the latte r
gain,high-frequency amplifiers is to prevent instability .
term which is ignored . Hence G = vo/vi = -R f / R i
It consists of adding phase-changing networks to th e
amplifier to lower its gain at frequencies where th e For the finite open-loop gain case ;

d /Rf
phase after feedback would cause oscillation .
I i = (v i - v n (/R i and I£
=(v o - v
Phase-shifting of the high-frequency response of a
high-gain amplifier is inevitable in circuits containin g
many transistors - as Cp . Amps . do . The technique use d
in taming these amplifiers is to ensure that the gain o f Ri Rf Rf
the system at the troublesome phase is less than unity .
or v i - v n = (vn - v o ) .Ri/Rf

So what is involved?
v i = Ri .( v n - v o ) + vn
Rf
The basic inverting amplifier uses a resistive feed -
back network as shown below and has a gain of -Rf/Ri - but vn = - v o/A, V . - Ri v o - v o -v o
assuming that the open-loop gain is infinite and that al l Rf( A A
other _`actors are perfect .

If, however, the open-loop gain, A, is not infinit e

is the case for a practical amplifier,and especiall y
Ri .vo(A +
I
11 -
vo
A

at high frequencies, then the expression is no longe r - v o . Ri . (l + 1\ + 1 .Rf 1

true . Normally the slight voltage, v , at the inpu t Rf A A Rt
terminal is ignored but now it has to e taken int o
account . 1 + 1Il + R I
v n is required to generat e Rf A I\ Ri/I
1
with a gain of A
Closed-loop gain is G = v o
vi - Rf r1 + 111 + Rf1 1
R' L l Ri/I
J
opr l.,p 11I
=- Rf 1
Gau .
- Ri 1
+1(1 +Rf 1
A Ri //

- Rf 1
Ri
i + 11Ri + Rfl
For an inverting amplifier the sum of the current s
A` Ri
at the inverting input is zero . i .e . I i + In + If = O .
 2 2

Now B = R i /(R i + R f ), so the actual closed-loop gain 0 is : - The diagram can be simplified to the asymptotes onl y
and is then called a Bode plot . Such a reducing respons e
is always accompanied by a phase-change - in this case 90 °
lagging due to capacitor Cs - but transistors themselves
do have phase-changes at very high frequencies . With a
G - - Rf l 1 resistive NFB network the phase, in this example, will no t
Ri 1
+ 1 reach '- 180° and the system will not oscillate .
AB
The closed-loop gain depends on open-loop gain as w e
have already seen and to give an expression for the closed-
For the non-inverting amplifier G is : -
loop gain of such an amplifier we have only to include a
factor for the H .F . loss due to a CR network .

This is :-
A e A
G + Rf 1 w
1 + jw/wo
(
Ri}- 1 + 1/A B
The closed-loop gain is .-
These equations show that the closed-loop gain is reduced.
if the open-loop gain is reduced .

Loop Gai n G --Rf

Ri
The factor AB in these equations is called the loo p
gain and is an important factor in amplifier calculations .
which becomes,
The error in closed-loop gain due to a finite open -
R_ +
loop gain is : - 1+ J(W/m>)
1 AB AB
1+ 1/A13 Ag + 1
The closed-loop 3 dB frequency, w, is obtained b y
which is approximately 1 - 1/A B equating the real and imaginary parts of the denominato

If Rf/Ri is greater than unity, B is approximatel y i .e . AB 1 w/w„ or AB +1 w/w o

Ri/R£ and the loop gain A/G . i .e . AB e A/G (A-G in dB ) AB + AB - AB

so co =wo ( 1+AB )
Bandwidth
This shows that the bandwidth of the closed-loop gai n
For a practical Op . Amp . the open-loop bandwidth i s greater than the open-loop bandwidth by an amount w o .AB
ris ,
that frequency at which the open-loop gain is 3 dB down
or the original bandwidth multiplied by loop gain .
on its value at low frequencies and a typical characteristi c
is shown for an amplifier containing a single time-constant . A 0PErv-LOP GAu

W. .A6 -''I
Above A and G are equal and loop-gain is zero .
woGL
The loop gain is seen to be maximum between d .c . and coo
and then to reduce at -6 dB/octave to zero at
w oC L
That is, it reduces because the open-loop gain reduces .

This is important in IFS systems because the improvement s

in stability, output-impedance and distortion are all directl y
proportional to loop gain . If there is no loop gain ( i . e
no NFB ) there can be no improvements )

Stability 0L = EiG/G = ( .0,A/A)/A B

The final slope is -6 dB/octave (which is 20 dB/decade )
and is known as the asymptote . The 3 dB frequency, whic h Output-impedancecL 2o01JAB
is at the junction of the -6 dB/octave and initial asymptotes ,
is w and is known as the break frequency or break point . Distortion 0L = D B
It i°s determined mainly by stray capacity, Miller effect, etc . OL/A
 23

Simple Lag Compensatio n

A
Unfortunately, multi-stage amplifiers such as Op . Amps .
do not have just one break frequency - they have many; an d sTews ccoseo-WeP GA,,
as each has a 9p° phase-shift capacity, the amplifier is G
virtually certain to have a gain greater than unity wher e 050mw_e
its phase-shift is *_ 18 0 0 (the conditions for oscillation ) Grow
even with resistive RFD . dg
in dB i s
he
A multi-stage amplifier response is depicted below :- 0 A - G (dB )
wn ebe do

Thus G has a minimum value which is still a considerabl e

gain . This is clearly inconvenient as the most useful Op .
Amp . functions are obtained when the gain is around the unit y
level, 0 dB .

How do we get rid of this excess gain ?

Designers of Op . Amps . endeavour to place the natural
breaks due to stray capacities, etc ., in ascending orde r The easiest method is to shunt away the very hig h
through the amplifier so as to keep the distortion an d frequencies with a single capacitor and this is the principl e
noise problems to a minimum . Such an amplifier gives ris e of frequency compensation .
to the following diagrams .
Frequency compensation enablesthe closed-loop gain t o
as be reduced at the expense of the bandwidth of the open-loop
Ai gain and this is effected by adding a capacitor to a certai n
A. point in, the amplifier - usually a base circuit - to form a
known break frequency or a phase-lagging characteristic .

a The characteristics of a CR network are shown below :-

A 1
-ed~atwe
, j
r..Jux r . 1/c .R, .t

(Oak AK'8waasi)
Thee' -■ddg/odete Cd,
GAM

o I C
0 -

site

The effect on the Op . Amp . response is shown in th e

next diagram . To get the optimum effect the -6 dB/octave
To7A a
slope of the capacitor network is arranged to coincid e
PHASE
with the first break point of the Op . Amp ., woi,where G min
intersects with it .

The new response extends to w 2 because . 02 no longe r

-~70
exists . However, wog is unchange( . (although A is lower )
It will be seen that the individual gain and phas e
curves add together and that the ' 180 0 condition occur s The curves simply add to give the total gain . Th e
for the -12 dB/octave slope . effect of the lagging network is to reduce open-loop band-
width and closed-loop gain (hopefully to below 0 dB)at w e? &
If a line representing a clotted-loop gain, G, is draw n does not affect closed-loop bandwidth but does increas e
on this plot to intersect the curve of open-loop gain, A , loop gain below wol .
at any place other than the - o' dB/octave portion, then th e
amplifier may oscillate . This is a general rule for th e C_ can be calculated from the expression : -
stability . Imust not cross A at hr a junction slope o f
more than6dB/octave,
l/CB int w ol.
1 + Al
 24

The phase–shift of the combination returns to zer o

above .2 . The extra attenuation of this method i s
arranged so that the original second break point, w
og,
is pushed below the required value of closed–loop gai n
whilst w2 is made the same as the original first brea k
frequency w
ol .
The va]ues of C and R are found as follows : -

The required attenuation, H w 2 = R + Rint (dB )

wl
R
which is approximately R in t R if the attenuation is large .

But, H = G and
min – Gregd Gregd _ A – A B

so H = G . However, G
For more feedback and less closed–loop gain C will b e min – (A – AB) min = A – w o2/w o l
larger . so Rint/R = A – w a AB – w
o 2/w ol – A + AB o 2/w o l
Unfortunately however, the closed–loop gain G is stil l
likely to be greater than unity by quite a considerabl e Thus R = Rint
amount . Luckily there is a better way to overcome this , aB – w
02f" ol _
Maximum–Bandwidth Lag Compensatio n
0 is found from w 2 = 1/CR, and since w 2 co ol ,
This uses part of the response of the Op . Amp . t o
attenuate the loop gain by putting a series resistor wit h C = 1/w
the compensation capacitor . o1 .`i

wl = l/0R General £ormulm which allow for phase margins, etc . ,

in t
are :
w 2 = 1/C R
R = 20(1 + Rf/Ri) [l C = (1 + Rf/Ri)/I0
0
Attenuation H = R + R in t
R
This method of frequency compensation gives the same
or R ., /R if atten . is larg e maximum closed–loop bandwidth as before but enables G n
Of 4h (71>loy,e V d6
to be made whatever level desired – at the expense
open–loop bandwidth .
ee mi

The original -6 dB/octave slop e

and the added slope are made into one long slope of -6 dB/
octave (to
wo2 ) .
Input Lag Compensatio n

Simple and Maximum–bandwidth lag compensations bot h

have the effect of slowing down the Op . Amp, in such a
way that maximum output cannot be obtained at h .f, n o
matter how hard it is driven . This is due bo the lag
capacitors being charged and discharged from relativel y
high–impedance sources within the Op . Amp . One way t o
overcome this problem is to put the compensation else
where – at the input . This also has the advantage that
the compensation no longer depends upon the Op . Amp . an d
the values of R and C can be made constant a er a rang e
of closed–loop gain .

Consider a non–inverting am p lifier with R and C

added between the input terminals of the Op . Amp .

RP
Rp = Ri .R f
Ri + R f

B Ri alp
Ri + Rf Rf
 25

1 = 2Rp + R ,or R, so 1/wiC = 2Rp + R

Some basic rdationshipe are , WC
and 1/w 2 C R
Ii =lc+If, Ica vi — vn If = vo —vn ,
Rp + R + 1/jwC Rf Therefore C = 1/w1 (2Rp + R) or C = 1/w 2R

vn = Ii .Ri = Ri(Ic + If) , vo = A . vn , for the upper and lower points .

Also v = A .Ic(R + 1/jwC) i .e . A times the voltage between Nov 1/w 1 (2Rp + R) = 1/w2R so w2R = w1 2Rp + w 1 R
the two input terminals . col
and R(w 2 — w 1 ) = w1 .2Rp, R e 2Rp .
w2 col
So v = Ri .Ic + D . (v o — vn )
n w

= Ie .Ri + v .Ri — v .R i
Rf n Rf 1
vn + v n .Ri = Ic .Ri + v o Ri w
Rf .Rf
It will be seen that these two formula Dare not dependan t
vn I1 + Ri= Ri I on the Op . Amp . As in the case of the maximum—bandwidt h
Rf
lag compensation w2 should be put at the original firs t
/ break frequency co
so v = Ri Ie + o Ri .Rf I Ic + v ol .
Rf~ _ \ Rf
w,,/w in dB gives the necessary attenuation in d B
1 + Ri Ri + R f required to lower the minimum stable closed—loop gain
Rf to the desired value .
Hence R is also 2Rp/(H — 1 )
Ri(Io .Rf +v o) Hence vn = B(Ic .R£ + vo )
Ri + R f The values for a 702 (see also further on) are given
but Io = v i — vn or Ic(Rp + R + 1/jwC) = v i — v n as examples
Hp + R + 1/jwC
Gmin is +40 dB, for a gain of 0 dB, H = 4 0

Ic(Rp + R + I/jwC) — B(Ic .Rf vo) For a gain of 0 dB,Ri = Rf = 10 KR . so R,=610,000/40

So +

= v i — B .Ic .Rf — B . v o =250 a

(the actual value is 220 Q to give a phase margin )
Ic(Rp + R + 1/jwC + B .Rf) vi — B.vo
C= 1/w 2 R = I/w o1 R = 1 / 4 x 10 6 .250 = 1 nF
Nov v o = A .Ic(R + 1/jwC) or Ic = v o/A(R + 1/ju0 )
This method of compensation has two disadvantages
and P .Ri = RP, s o
when used with voltage—followers . A value of Rf has t o
be included, and at h .f . the very high input—impedanc e
. (2Rp + R + 1/jwC) = vi — B . v o becomes low as C becomes low impedance .
A(R + 1/jwC )
Lead Compensation
. (2Rp + R + 1/jwC) + B)_ v i
(A(R + 1/jwC )
vo1 Most of the higher—performance Op . Amps . have two
Gai n = v terminals between which may be connected a capacitor t o
= 1 give phase advance or phase lead .
.(2Rp + R 1/jwC) + B
A(R + 1/jwC ) This requires a split series resistor between stage s
within the Op . Amp . The ratio of Rinb2 to Rin4l sets
A .( R + 1/jwC the attenuation .
'2Rp + R + 1/jwC j

1 + A .B(1 R + I/,jwC
12Rp + R + 1/jwC
Comparing this with \ A which is the expression fo r
1 + A .B the gain of an amplifier ,
there is a modifying factor :
C
R + 1/,jwC
2RP + R + 1/jwC

This factor is evaluated in the same manner as befor e t9o°

by equating the real and imaginary parts of the denominator ,
but in this case there are two break points .
O°
 26

ml is placed at the second break frequency of th e With simple lag compensation, 0 .1 µF to earth gives a
Cp . Amp, and the required attenuation is (dB) . 0 dB bandwidth of 501 KHz and m is at 250 Hz whilst A i s
.03/mo2
70 dB . This form of compensation is thus ideal for l .f .
This places at mo3 .
m2 integrators or other l .f . applications, but little else .

With maxir,,m-handwidth lag compensation the 0 dB band-

Hence C . 1/m,, .R .Rint which is small . width is raised to some 4 MHz . is now 50 KHz and ,v •• 2
int = l/Wo3 mtt
800 KHz . i .e . a four-octave imprbvement giving 24 dB o f
attenuation . C is 5 nF and R 40 Cl .

The effect is to make a long slope of -6 dB/octave

For a 20 dB closed-loop gain C is 1 nF and k 220 C l
from m to w , and to push the -12 dB/octave slope u p
to wo3 ol In fdct, there is no -12 dB/octave slope at all . giving a bandwidth of some 6 MHz .

For 40 dB gain C is 100 pF and R 2 .2 KC) and the band -

width is 7 MHz .

Generally for the 702 the values of C and R are give n

bz
W, 4a,3 R_20(l+Rf )
`` Hi
C = 0 .01(1 + Rf/Ri) µ F

With the 702 using lead compensation, the closed-ioo 2

bandwidth is some four-times greater than using lag comp-
ensation only, but some lag compensation is required belo w
40 dB closed-loop gain .

LEAD Cen P.

CL
This extends the bandwidth in the same ratio as th e Rp = Ri .Rf .
RI + if
open--loop gain is reduced . The new closed-loop gain ca n
be lower by twice this amount and the loop gain greater .

This method of compensation gives a wider closed-loo p

bandwidth than that provided by lag compensation, but a
compromise between this and a higher loop gain (and less
noise) is possible by using smaller amounts of both lea d
and lag compensation together .
'--M/W---d'S,NVVh d , vo
It is not easy to achieve satisfactory performanc e
with lead compensation alone as w has to be placed wit h
fair accuracy and this is not easy at the higher frequencies .
It is all too easy to get part of the -12 Ad/octave slop e
above C is made too small .
Gmrnif
.
Phase margi n Typical figures are

As a guide to a typical Up . Amp . response, the 702 Rf 10 KR, CL 50 pF, Gain 0 dB, iiandwidth 23 MHz, R 200 ii ,
has the following value s and C 1 nF .

wel 800 IQiz, a)02 4 MHz, mo3 40 MHz, and -180 °

Rf 10 KO. CL 50 pF, Gain 20 dB, Bandwidth 26 MHz ,
occurs at 14 MHz with a gain of +35 dB . Lf . gain is 70 dB R 200 Cl and C 1 oF .
so that the loop gain maximum is also 35 d•: before oscillation s
can occur . In actual practise the loop gain cannot be made Rf 10 Eli, C 50 pF, Cain 40 dB, Bandwidth 28 MHz ,
higher than 20 dB without causing a response peak in th e R and C not, required .
closed-loop gain due to an inadequate phase margin . Thi s
means that -6 dB/octave slope is not approached closer tha n
some -3 dB/octave (it is after all a smooth curve and no t A low-priced Op . Amp . with no built-in compensatio n
an asymptote in reality ) is the 702 . This has tao terminals for compensatio n
purposes which are labelled LEAD and LAG .
Practical compensation (using 702 )

In all the previous explanations the phase margin was

ignored (i .e . it was zero) but in practise a phase margi n With some other types of Op . Amp . (e .g . 709) the la
g
of less than 90 will cause a peaked response at the atten - compensation capacitor is not earthed but raturneAto anothe r
uation point . A satisfactory margin value is 45° giving a
point in the amplifier .
+3 dB peak . This corresponds to a loop gain of 20 dB wit h
the 702 .
 27

Load Capacity Input comp ., Bandwidth 800 KHz, Slew-rate 30 V/µs ,

Noise 170 pV .
The capacity of the load on the output of the Op . Amp . (both at unity gain )
has an effect on the phase of the NFB at h .f . and the lag
due to this is effectively added to the phase curves fo r The 741 has a slew-rate of 0 .5 V/µs which gives a
the Op . Amp . unity gain bandwidth of 22 KHz . This is not much use fo r
T V work as it is generally assumed that some ten harmonic s
It can be minimised by increasing the phase margin b y are necessary to reproduce a waveform faithfull y
increasing C and decreasing R (both by a factor of two o r
m .re ) or by putting a small capacitor across Rf to give This really confines the use of the 741 to i .e . an d
some phase lead to effect cancellation . l .f . . It is difficult to get one to handle a line-rat e
sawtooth waveform with any satisfaction .
Stem-rat e
The 741 is a very useful Op . Amp . though despite thi s
Nct the mortality-rate of Op . Amps ., but an expressio n drawback as it has no compensation to worry about . Quit e
literally it is used without worrying about other components ;
for the maximum rate-of-change at which the output of th e
Cp . Amp . can change in response to a step-function input . as in the voltage-follower where there are indeed none at all .
- i .e . the gradient of the slope .
All this compensation may seem a bit frightening but i t
The signal rate-of-change i s is made very simple for us by the manufacturer . All we hav e
to do is to look up in his tables our value of G and read of f
directly proportional to the ampli-
tude but the Op . Amp . with lagging the corresponding values of C and R for the different type s
of compensation . Of course, there is usually no muc h
capacitors has to charge and dis-
charge these at the signal rate an d information and so many symbols that this is not all tha t
there is a limit to each particula r easy . But that is another problem
point in terms of charging current .
If this rate is exceeded then the
Op. Amp . cannot catch up with the
signal until the signal slows down again . This effect i s
expressed in Volts/µs . Schmitt Trigge r

At high frequencies then, there has to be a compromis e So far in this series on Integrated Circuits the Op .
between amplitude and frequency - you can't have both . Amp . has been considered only with Negative Feedback, NFB .
What is the effect of Positive feedback ?
The spew-rate and the bandwidth are often quote d
separately from the full-output maximum frequency whic h This is of course feedback from the output to th e
non-inverting input . With no feedback at all the ver y
can be very mis-leading . Likewise the slew-rate is
often quoted at a high gain figure instead of Atunit y high gain of the Op . Amp . usually ensures that the outpu t
will be in a saturated state due to inherent imbalance s
gain where it is much less .
in the input circuitry . There is only a small region o f
Maxim frequency for full output,with no distortion , input voltage near Ov where the amplifier can in fac t
and clew-rate are related by the equation shown belo w amplify - this is (+Vsat - Vsat)/A . It should b e
(the gain, being unity) . - remembered that Op . Amp . supplies are normally two-rai l
or positive and negative .

Positive feedback reduces this voltage range to virtuall y

Slew-rate S - d va - m .V = 2scf . V
nothing so that the output is always in one saturated stat e
or the other and the input voltage range can be considere d
N6fse and comtensatlo e to be a single voltage . Positive feedback does this by
assisting the input voltage change - causing regeneration .
The compensation network affects the noise performanc e A circuit of this type is known as a Schmitt-trigger o r
as lagging compensation attenuate s. the h .f . components o f level-detector .
both noise and signal .
The addition of PFB causes a hysteresis effect whic h
Input lag compensation actually worsens the signal-to- means that the input voltage required to change the outpu t
anise ratio since the network does not attenuate Op . Amp . state is no longer the same voltage for both directions o f
acme - only signal h .f . A factor of 20 AS is typical . change

At unity gain this may be even more .

Noise and Slew-rate performances then ore are bot h

dependant on compensation in opposite ways and a compromis e
may have to be reached in cone appiications .by using bot h
type; of compensation .

A typical performance of the 702 is given :-

Lagging coop ., Bandwidth 10 KHz, Slew-rate 0 .35 V/µs ,

Noise 15 µV .
 28

The voltage at which the change occurs is called th e The oscillator can be symohron ; s d by inserting narro w
threshold and has the value *- Vosat RiARi + Rf) . pulses into the non-inverting input .

The circuit is useful for sharpening up waveforms suc h

These pulses may be either positive or negative-goin g
as slow pulses and sine waves .
and will synchronise positive and negative edges respectively .
It is generally preferable to use only one polarity .
Simple Listable or Latc h

The schmitt-trigger circuit forms the basis of a simpl e

bistable in which a differentiating input circuit is used .
This passes only the edges of the input pulses and thes e
make the Op . Amp . change state if their voltages exceed the
threshold levels . The mean level is Ov which is withi n
both threshold levels and so to change states alternatel y L_
the trigger pulses must also be alternate in polarity .

The circuit is useful as a latch or memory . C R

-11t.a eld _ _t _ _ _ The frequency stability with supply voltage is goo d

RL - unlike the common transistor multivibrator - because i f
I~V~ w i the supply is, say, halved the the charging current i s
oy Th e
also halved but so too is the threshold voltage .
switching voltage is therefore reached in about the san e
time as previously .
i
Monostable -1

The multivibrator may be turned into a monostah.le, o r

-' 'o .st one-shot, merely by adding a single diode across the capacitor .
This prevents the circuit from being self-acting in one
QSCILLATORY CIRCUIT S direction .

Relaxation oscillator or Multivibrato r

A schmitt-trigger type of circuit is partway toward s

being an oscillator - all that is required is a time-constan t
to delay the switching action in a predictable manner .

4 D
In this case the voltage across C cannot go more positiv e
than about 0 .6 V which is arranged to be less than th e
threshold voltage . The trigger pulse is negative--goin g
in order to make the output go negative .
The output will change state for a time : -
c
The operation is that the Op . Amp . saturates at som e t = CR log e (i + Ri/Rf )
voltage *-Vosat The voltage at, the non-inverting inpu t
. Reversing the diode gives a reversed output pulse an d
is then determined by the feedback ratio and is '-Ve Ri the input trigger must also be reversed .
sat Ri + R f
If the Op . Amp . is in positive saturation then the fe d Heave table - 2
back voltage is also positive and so C charges positively .
via R until Vc reaches +Vo w„+ . Ri/(Ri + Rf) . Another type of moves table can be made in which th e
period is determined by a reference voltage .
The amplifier output then changes state because th e
inverting input starts to go more positive than the non - The timing capacitor is placed in the Pith path an d
inverting input . That is , the output goes negative . the output is normally at +Vosat' The inverting inpu t
C then begins to charge towards -Vosat .Ri/(Ri + Rf) and so on .
will be at -Vref (as is the other input) .
The period of oscillation is : -
The input trigger pules must exceed Vref in order t o
unsaturate the Op . Amp . i .e . it must be positive-going
2CR log 1 + Ri/(Ri + Rf)
2CR log e (1 + 2Ri/Rf ) with an amplitude greater than Vref . The output voltag e
l - Ri/(Ri + Rf ) change from + Vsat to - Vsat is passed via C to the non-
inverting input and C charges via R until the voltage a t
If Ri = Rf then t = 2,2 CR econds .
 29

for example, then the knee of the diode curve causes

the non-inverting input equals Vref . (Vref must be les s
considerable distortion, because the output is not linea r
than -Vo sat )
in this region . The ideal diode has no forward voltag e
The period of the output is CR log e (2Vo ref ) drop of course .
sat/ °
Placing the diode in the feedback loop of an Op . Amp .
and the output period may be longer or shorter than the
effectively divides the forward drop by the open-loop gain .
input trigger pulse . and for most purposes it is then negligible . Very lo w
amplitude signals can then be detected with little distortion .
Sine-wave Oscillator

Sine waves can be obtained from an Op . Amp by using

a Wien Fridge network . This has an attenuation of 3 time s apJ
ands sera phase-shift at the null frequency . The frequency
at resonance is given by 1/2,tRC Hz . Atten . = 1/(1 + 2R1/R2 )

The network has to hr placed in the non-invertin g

feedback loop and to maintain oscillation the gain o f
the Op . Amp . must be 3, i .e . Rf/Ri in the inverting
feedback loop must be 2 . The gain must be precisely
3 otherwise the oscillator either will not start or wil l
saturate . One any of stabilising the gain at 3 is t o
If the input voltage is negative with respect to th e
use a thermister for Rf (the R53 by STC is suitable )
non-inverting input (earth) then the output of the Op, Amp .
must be positive and so the diode must be conducting .
The output voltage is exactly the inverse of the input a s
Wien Network the diode drop is overcome by the Op . Amp . output bein g
that much more positive than the output point . The
R2
forward resistance of the diode plus Rfmahesthe gain o f
the Op . Amp . greater than unity but the output is atten-
uated by the same amount due to the inverting input bein g
a low impedance . Hence the gain is Rf/Ri as usual .
It is seen, therefore, that the diode drop is eliminated .
Re R£ - 2Ri

If the input is positive the the diode is non-conductin g

For 1 KHz and 3V output pp, R=10Kfl and C= 16nF ,
and the output point potential is that of the invertin g
3i-47X2 and R£ = R53(thermist or) . Both amplitude and
input which must be that of the non-inverting input, or OV .
frequency are stable to within 0 .1 % .

The output point thus has two values of impedance -

Crystal Oscillator
low or Rf . A voltage-follower should therefore ideall y
follow a half-wave rectifier .
The crystal is used to provide positive feedbac k
and. resonates in its series mode - approximately 0 .1 %
A number of half-wave rectifiers can be joined togethe r
low in frequency . The series capacitor will enable th e
in the usual manner to form full-wave rectifiers, etc . ,
frequency to be raised to the correct frequency .
merely by commoning the output points . Such a circui t
gives an output which is the lowest of the inputs . In
other words, a non-additive mix . This system can b e
useful in a pattern generator, and is in fact an analogu e
NAND gate .

Constant-current sourc e

A constant-current source is one whose impedanc e

C is high so that the voltage varies whilst the curren t
does not when a variable load is present . One o f
The following conditions should be satisfied fo r the most common uses for such a source is to charg e
good performance : - capacitors so as to form a linear sawtooth waveform .
Another is to form the 'tail' of a long-tailled pair .
R1 = Ri/Rf/(Ri + Rf), Rf '-f 39 Ill, Rf/Ri = 1 .35 an d This enables the gain to be kept high .
Xc ``Rf/500 . CV should be about 5 pF for a 5 MHz Xtal .
The normal method of making a constant-curren t
source is to use a transistor as shown . This ha s
some disadvantages amongst which are the use of a diode
MORE USEFUL CIRCUITS - Rectifier s to compensate for the forward drop of the transisto r
which varies with temperature, and the fact that th e
The high gain of an Op . Amp . can be put to use in current has to be set with a variable resistor R .
a half-wave rectifier to reduce the forward drop du e
to a semi-conductor . For a silicon diode this is about The Cr . Amp, gives us a convenient voltage-variabl e
0 .6 V and for a Germanium diode about 0 .3 V . If low source which is temperature-independant and as an adde d
voltage s i gnals are to be restified,as in most detecto rs advantage can be given an adjustable impedance .
 3o

gown to 0V by the switch, descends at the same rate a s

ry it ascended . Another voltage detector is then used t o
reverse the bistable again, and so on . This generates
a triangular waveform, This generator can he used . for
pattern generation . 00 Mier ewe /aPEA4SO
IC
oft.
Ji.
-- \yam p ~ + —i
Gesta t
l Ryd., .

(ems) Vs RI z {— Rf -v
> JjAyrr
L .r e
t

+v ; pen I
The Op . Amp . can be ccnsisdered to have a gain of + 2 p0
4
at the non-inverting input since the PIFB resistor is th e ru ViY —
same value as the input resistor . On the other han d
R{
there is positive feedback to the same input which i s
attenuated by 2 because of R2 and N . Any change at th e
non-inverting input is thus accompanied by an, identica l
change at the same point due to the Op . Amp . This can It is evident that this form of constant-curren t
be considered as a resistor with the same voltage at bot h source is very useful and it has two more advantage s
ends - it has infinite resistance . The non-inverting yet, The first is that either positive or negativ e
input thus exhibits infinite resistance which is th e currents may be obtained by positive or negativ e
condition for a constant-cu rrent source . Another name voltage (low impedance) to Rl or by negative or positiv e
for this principle of 100 % feedback is bootstrapping . voltage (low impedance) to Ri . The second is that by
Cvm'tsi( nI = 'tr varying the ratios of the feedback arms the linearity o f
Re a sawtooth waveform can Abe varied in both directions .
R, 2 R f Furthermore, the linearity control is to a large exten t
R, R C independent of the amplitude, i .e . it does not cause an
amplitude change . This system of sawtooth generation
is therefore ideal for a scan generator .
R Rf

Errat a

Two diagrams were interchanged in CQ-TV 80 it- part 1 0

of this series . These were the last diagram on page 1 0
and the first diagram on page 11 .
A load connected to the non-inverting input will .
receive a current of +V/R1 and although the voltage Also in CQ-TV 80 plO, the dif£erentiator gain-limiting
across the load may change, its current will not . resistor Ri should be in series with Cl - net parallel ..
The maximum input voltage is Vsat/2 because the gain i s
two . The input voltage could be applied via th e
inverting input instead and would then give a negativ e
current . Next issue

This circuit provides a convenient way of generatin g The next part of this series wail examine enure mor e
sawtooth waveforms as the next diagram shows . The trans- uses of Op . AM-pa ., also better Op . Amps, than the (41
istor is used to discharge the capacitor to start th e and will include some other types of Linear ICn shic h
sawtooth . The voltage across the capacitor is directl y have been held ever from this time ,
proportional to the current in R1, which is proportiona l
to +V, and so a positive ramp results as C charges up . It is also hoped to describe the (-segment decoder s
and i.ndieaters in the next issue, a.s well as some mor e
The sawtooth level may be detected at a certain leve l digital circuitry ,
by means of a net mitt-trigger or similar level-dependan t
circuit and the output used to turn on the dischargin g Reference s
transistor . This results in a free-running generator .
A uni-junction transistor could be used too . Manufacturers' information shhets for IC date .
~ raft Wireless World, Fob 1969 - Series on Operational Amplifier s
by G .B .Clayton, B .Sc .,4 .Inst .P . (in nine carts . )
Mullard Linear .Appliaatior Note TP 308 6
SGS/Feiiehilf, The application of linear micron-resit s
RCA, Linear Integrated Circuit Fundamentals - Technica l
Series IC-40
Linear Integrated Circuits . Theery and Applications b y
Jerry Rimbinder . John Wiley and Sons .

Acknowledgemen t
R5 Rf
If a histahle is driven from the voltage-detecto r The author wishes to thank the Directors of EMI Soun d
the output can be used to change inputs to the constant- and Vision Equipment Division for permission to publis h
this article .
current source so Mist the ramp, instead of being taker.
 31

TACAN, VOR and LRCO station with a lecture ,

POSTBA G followed by an auction of gear . Sounds a
well organised group which could be take n
as a model for many others . Keep up th e
Chris LonR from Victoria, Australia, descri- good work :
bes himself as a " dedicated experimenter in
the field of video electronics " . He ha s Gareth Evans G8DXY from Bristol has written
been interested in this field since the ag e to point out a ghastly editorial error i n
of 14 and his experimental studio now incl- C Q - T V 80 ; the photograph in the Con-
udes, among other interesting equipment, a vention report allegedly of Nigel Walke r
range of mechanical scanning equipment fo r and his colour equipment is actually one o f
low definition tv . These are all based on Gareth fiddling with Nigel ' s colour equip-
a 32 line standard, and a recent 30 lin e ment : In Gareth ' s own words " I think a
Baird system recording made by Chris o n small apology is due to Nigel" . Too right :
inch tape is now being used by the I .B .A . The Editor humbly apologises to both of you .
in their " Television Gallery " . Although
interested in high definition tv (he ha s Ladislav Vik from Switzerland has written
built a 1,500 line flying spot scanner) th e telling us more of his experiments with PI N
main interest is low definition televisio n Photodiodes for Flying Spot Scanners . He
(L .D .T .V .) and a recent extension of thi s hopes for success along these lines very
work was a plan to transmit moving 30 lin e soon, but has heard that phototransistors ,
pictures from Australia to Britain . Al - previously thought to be too slow, may no w
though supported by the Wireless Institut e be feasible due to new circuitry develope d
of Australia, the plan was unfortunatel y by Siemens . Ladislav has also used the
frustrated by what Chris ' English coll- GW6JGA/T scan circuit published in C Q -
eagues describe as " condescending opposi- T V 78, with some modifications ; he ha s
tion by the T .S .G .B ." in Britain . It i s added a current amplifier for the scannin g
now found much less restrictive to carr y coils, and also reversed the diode D1, re-
out " transmissions " by means of 4 inch tap e sulting in negative going blanking at th e
sent through the post . An attempt is now output, to suit his own experiment . Fo r
being made to whip up some more interes t a 625 line scan unit he has developed an -
in L .D .T .V . and to get some more people t o other unit using a faster LM201 op amp .
become involved in tape exchanges .
N .W . Smith ZUCJ from Huntley, New Zealand ,
Franklyn Brooker9Y4VU c /o Instrument Dept , is a new member of B .A .T .C ., and tells u s
Texaco, Pointe-a-Pierre, Trinidad asks that he uses the C Q - T V S .P .G . to driv e
B .A .T .C . members to note that he is avail - his one inch vidicon camera . The S .P .G .
able on any band for SSTV contacts . worked first go he says (well, almost, he ' d
only forgotten one link which had to be re -
soldered :) and apparently several other peo-
G, James McKee Jr . WB6ROP from the South-
ple in the area are also building it, on e
ern California ATV Club has just joine d of them being ZLITFX . As Arthur Critchle y
B .A .T .C . and has sent us a recent copy o f points out in his article, this S .P .G . really
their monthly Club Bulletin - thanks Jim : is being built in large numbers . Let ' s hop e
The Club has regular meetings - the Dec - it gives you long service, Brian :
ember one included a tour of a nearby
 32

David Wilkinson of New Eltham, London wrot e

recently with a few topics of interest t o ADVER T S
readers . First, the Multiburst Generato r
circuit printed in C Q - T V 80 had due t o
an oversight, the horizontal cross-straps o n
the three right hand monostables omitted .
They should be strapped as per the left hand
EQUIPMENT REGISTRY can help out with you r
one (but not have an output taken from the
problems . If you have surplus gear, or i f
strap as does the left hand one) . Secondly ,
you want a particular piece of equipment ,
readers may have seen recently adverts for
send details (enclosing a stamped envel-
an I .C ., the XR205 Monolithic Waveform Gen-
ope) to Alan Watson who ' s address is pr-
erator ; here is some information about it .
inted on page I .
It contains a voltage controlled multivib-
rator, a balanced modulator, a buffer ampli- ADVERTISING RATE S
fier, and more interesting, provision for a Back page £12 .0 0
sinewave output . This latter facility i s Full page £10,0 0
presumably achieved by applying the triang- Half page £ 6 .0 0
ular wave output to a suitable diode network . Member ' s small advertisements are free ;
Out of curiosity, an attempt was made to us e a charge of 10p per line is made to no n
this as a video sweeper . It was found tha t members .
the maximum output frequency was about 3 .5MH z
but only a 3 :1 sweep range could be achieved .
FOR SALE
(At lower frequencies 10 :1 can be achieved) ,
Plumbicon scan and focus yokes . Ex-EM I
Also the output level falls somewhat abov e
cameras . Small quantity in various state s
2MHz . In fairness, this performance is i n
of completeness .
accordance with the data sheet .
One vidicon yoke .
On the subject of the C Q - T V S .P .G . ,
mention was made in C Q - T V 80, page 13 , One staticon (vidicon side-pip) O .K .
of the difficulty with phase modulation whe n Four 8'-z" CRT's orange long-persistence phos-
mains locking . This can be greatly improve d
phor(Thorn/AEI M21-13LE or V3190/T13) suitabl e
by adding an anti-phase a .c . component fro m slow scan? )
the other side of the bistable (see Fig . 18 ,
Four I0 lens blanking plates and one len s
C Q - T V 77, page 11) .
mounting ring with gear ring plus host o f
lensy bits .

Scrap Lektrokit boards with components- trans-

istors, etc . Also other scrap beards galore .

Pair of CRT ' s 5 " x 4 " rectangular for viewfin-

ders .

One pincushion correctorboard for BRC 300 0

Colour TV . £3,0 0

A .W . Critchley ,
The 47 F should be a reversible type, The 70 Sussex Road ,
330 ohm resistor is best adjusted for min- Ickenham, Uxbridge ,
imum modulation . The idea came from a Middx . U810 8PN
fairly vintage Sylvania S .P .G . Tel . Ruislip 39148
 33

t slow scan televisio n

Slow scan is the most exciting newcomer since sideband ;
join the ranks of sstv ' ers now :

Chapters are headed Principles, Background, Monitors ,

F .S .S . and Cameras .

Circuit diagrams and constructional details .

ONLY 25p (plus 3p postage )

fro m
B .A .T .C . Club Sales .
"Kyrles Cross "
Peterstow
Ross-on-Wye , This booklet is the first of a series to be published by C Q - TV ;
Herefordshire . further issues will be announced in this journal and will includ e
a reprint of Arthur Critchley ' a articles on Integrated Circuits .

PRINTED CIRCUIT BOARDS FOR THE C - T V SPG TUBES FOR ATV Save £££££ 0000 send
SPG Board £1 .50p list of your ATV tube needs for £££££ sav-

Genlock Board £1 .50p ing quote to TUBES INTERNATIONAL

120 Central Buildin g
Please send cash, together with post and
packing, with order to : Wainwright, Ak . 9978 2
U .S .A .
A .W . Critchle y
70 Sussex Road , FOR SALE
Ickenham , 10 x 14 way vision switching matrix .
Uxbridge, Middlesex . Contains multiway switches, relays and
sockets, needs simple attention to the
push buttons . Can easily be split int o

WANTE D smaller units . £12 plus carriage .

4CX250K Valve . Buy or swop for vidicon , Used 19 inch shadow mask tube, working

photomultiplier or what you want . condition . £15 plus carriage .

Gordon Sharp ley GSLEE/ T David Wilson
52 Ullswater Road , 70, Moorshed Roa d
Flixton, Urmston Maids Val e
Lancashire . London W9 1LG .
 34

Club Sales Price Lis t

Camera Tubes English Electric P849 Amateur Grade £10 .50£

E .M .I . 9677 Amateur Grade £10 .00p
9728 Amateur Grade £10 .00p
E .M,I,(integral mesh) 10667 Amateur Grade £ 8 .00p

41 inch Image Orthicon 9564 & 956 5 £10 .00p

(older type with " sticky " target)

Ex studio vidicons . Various types, mostly

separate mesh . When available £ 5 .50p

Deflector and Focus Coil Assemblies per se t £ 7 .50p

Vidicon sockets (paxolin ) .17p
Vidicon sockets (moulded ) .25p
"C" mount in Aluminium for use with tine lens .50p
931A Sockets (including post & packing) .10p

Lapel Badge s .20p

Lapel Badges with Call sign(to special order ) .30p
Adhesive emblems (for decorating gear with Club badge ) .15p
Windscreen sticker s . 6p

B .A .T .C . Notepaper and envelopes (100 sheets) £ 1 .00p

B .A .T .C . Reporting Chart (a visual scale of video noise) . 6p
E .E .V . Co . Ltd . Camera test charts £ 1 .50£
Film strips of C Q - T V . 10 issues on each fil m
(Please state which decade you require eg . 41-50 etc .) £ 1 .00
Back nos . of C Q - T V as available Members price .20p
Non-Members price .25p
"Slow Scan Television " by B . Arnold G3RHI .25p
Please send cash, together with post and packing, with order to :

B .A .T .C . Sale s
"Kyrles Cros s "
Pe ters to w
Ross-on-Wye ,
Herefordsnire .

After April 10th, when Value Added Tax comes into effect, there will be a 10% increase
in the price of most items . This will apply immediately to camera tubes which are ordered fro m
the manufacturers when requested . We shall try to keep prices as low as possible and ther e
will be no increase on goods already in stock . As stocks run out however, the new supplie s
will carry 10% V .A .T . and may also carry an increase due to the general upward trend of prices .
Postages are now a considerable item and you are requested to send something towards the cos t
of postage and packing with the goods you order . Please note that we do NOT intend to issu e
C Q - T V 71 - 80 as a filmstrip .

P L E A S E N 0 T E T H I S L I S T C A N C E L S A L L O T H E R S
TH E
CROFTO N
CAMERA
Designed by Mullar d

KIT Educational Service .

Complete kit of parts to construct a good

performance low cost Vidicon camera . A
comprehensive construction manual i s
supplied with each kit (available separatel y
at 65p) .

Ideal kit for the amateur who wants t o

incorporate his own design mods . Case has
plenty of room to incorporate additiona l
circuitry for a sampling slow scan T .V . camera .

Size : 4 1/2" x 7" x 11" . Weight : 6 1/21b .

Two output sockets (Belling Lee) are provided .

Two 4 pole changeover slide switches and a
six way F & E chassis mounted plug, which although not used in the basi c
design, are provided for constructors own use .

Complete kit, less lens and tube, costs £57 .00 plus p .p . £1 .25 .

A UHF modulator kit is also available which has been designed to be

housed within the camera, at £6 .00 plus p .p. 30p .

Used Vidicon tubes available from £3 .50 upwards depending upon quality
p . p . 25p .

CROFTON ELECTRONIC S
15/17 Cambridge Rd . Kingston-upon-Thames, Surrey KT1 3NG