TECHNICAL FEATURE RON STONE, GW3YDX . E-MAIL: RON@VINECOM.CO.UK JULY 2010.
RADCOM
The GW3YDX Super Moxon
Adding extra directivity to the Moxon Rectangle
for 6m, 4, and 2m
Continuingto use the Moxonrectangle,
the fairly broadfrontal lobeof the antenna
(seeFigure2) of 80° between3dB power
pointswas sometimesnottoo goodin QRM
when beamingto Europe.
IMPROVEMENT. Something better was
needed,but how couldthis be achieved
withouta greaterwingspan,yetwith a
worthwhile increaseingainfor not a huge
increasein boomlength?Lyingin bed one
night and thinking about radio antennas
(asonedoes)the ideacame to meof adding
directorsto the Moxon,but in the form of
anotherrectangle,ietwodirectorswiththe
ends bent backandjoinedwith an insulator.
Severaleveningswerethen spentmodelling
the antenna usinga combinationof 4NEC2
and EZNEC+.Foran increasein boomlength
to just under2m (just overdoublethe original
boomlength)and no increaseinwingspan,
another3dB gainwasachievedfromthe
modelling,with a 26.5dB frontto backratio
PHOTO 1: Completed 4m GW3YDX Super Moxon. and a VSWRof lessthan 1.5:1 between
50.0 and 50.3MHz when the modelwas
MOXONFAN. The author is a keenenthusiast BASIC MOXON DESIGN. Making the Moxon optimisedfor 50.1MHz.
of the Moxon Rectangle antenna, invented rectangle was not difficult. There are some Figures3 and 4 illustratethe modelling
by the late Les Moxon, G6XN.ln its basic useful design formulae available that are resultsobtained.Notethe decrease in -3dB
form it's easy to build and is a great performer. quite accu rate. The best one so fa r fou nd is powerpointsto 60° comparedwith80°for
The reduced wingspar.1 of the rectangle also Moxgen (Figure 1), which allows input ofwire the original.Thisnarrowingiswheregain
appeals to the QTH-restricted UK radio gauge and frequency and that results in a comesfrom. Frontto backratioof around
amateur and it is a surprise that the antenna dimensional guide. Moxgen is downloadable 26dB is very respectableandthe patternhas
has not become more popular. as free software from [1] and, most usefully, a niceclean'light bulb' shapeto it,withno
Spending much of the day in the allows creation of a model in either NEC or minorlobes. Althoughmodellingindicated
workshop, I wished to keep an eye (and ear) EZNEC formats for further experimentation. that a 380 feed impedancewas ideal,
on the 6m band one June. Something is
often happening on six, so I wanted a simple ;:: Moxon Rectangle Generator @
antenna to monitor the band. Although my
neighbours are quite understanding of the
structures that go up from time to time to
~
Frequency MHz \Noesize ji'2:7" ~ I ~e I ! .!ienereteModell:
be tested, this would be a semi-permanent -Fonnal-
r
i
A 2150.1mm . : r. EZNEC
antenna and thus something was required
that was not too visually obtrusive. A Moxon A I 81 283.6mm
r NEC
rectangle was built for 6m and put on a short
mast outside the workshop door. An FT-847
cl 101.5mm
(a trusty test radio for antenna projects) was Driven
installed for monitoring the band. Element
Much interesting DXwas worked,
including a memorable evening in late
'~~I1 DI
E j
413.6mm
798,7mm
June where more than 80 stations in the
Reflector - RetUb Unk---"'j
USA were contacted, extending as far as
west Texas. This was just with lOOW from
a poor VHF QTH, and there seemed no
difference in results compared with the
11 rFeet
r Inches
r Met",.
r. :M5,"""'~
-------
Emt
Close
m__m ~_M m
(alleged) kilowatt-and-Iong-Yagi G stations
on the band. FIGURE 1: Calculating Moxon Rectangle parameterswith Moxgen.
I RADCOM. JULY2010 TECHNICALFEATUREL
TABLE 1: Tubing lengths for 6m, 4m and 2m versions of Figure 5. All dimensions in
mm,measured to tubing centres.
A B C D E F G H J K L M
- 6m 2160 395 280 105 290 310 60 2140 0 780 1201 1861
4m 1572 275 175 110 195 202 43 1572 0 560 860 1310
2m 730 135 86 55 82 90 12 730 0 276 434 615
~ Pattern (H). .. . grg:rgJ ~ Pattern (f4) l:Ji'E[,rgJ
Show F,.,field p"." "eid C"""""e 0penPF PIo( Show F,., fiekj ,.""" ',,'0 COmo,.,. 0penPF PIo(
T oI-ga;..
50.2MHz
[dB;] m Horizontal plane
ToI-gaio[dB;[ '05 m - HooUontai plane
PHOTO 2: The 2m version of the Super Moxon
is just 30" x 25".
practical models have been fed with 500
cable and VSWR plots that follow the model
graphs have been obtained with just slight
adjustment of the driven cell element lengths.
VSWR bandwidth is probably a little narrower
than comparable Yagi designs, but at below 285 -4Q < dB; < 6.05 .20< <13; < 9.04
2?0 285
tot.. gain PI1i;O
1.5: 1 for the most-used part of 6m is very tot.. gain 1'I1i:{J
acceptable. The author has quite extensive FIGURE 2: 4NEC2 plot of Moxon rect~mgle FIGURE 3: 4NEC2 plot of Super Moxon radiation
knowledge of Yagi designs and so far (this showing fairly broad frontal lobe and 80° pattern. Note narrower frontal lobe and improved
tempts fate of course) has seen no 6m antenna 3dB points. forward gain with very smooth rear pattern.
design with comparable performance on
such a short boom. A regular Yagi with the hose clamps for
same gain would need a boom length of fine adjustment,
nearly 50% more and a turning radius nearly particularly if
double of this design. One can truly say that other antennas
this design packs more dB into its size than are nearby. It
2
anything else so far realised. would be most
interesting to hear
BUILDING THE PROTOTYPE. The next of constructors
stage was physical implementation, which using this design
was done with aluminium alloy for the on other bands.
elements and fibreglass rod for the split 10m is currently
driven element and the element-end in the doldrums,
insulators. This is a lightweight antenna, but a 10m version
easy for one person to manage, and only of this antenna or
a 1" square boom was required. of the basic Moxon
Construction of the antenna was 50.05 50.1
rectangle would
principally with-W' aluminium alloy, with be the most space- FIGURE4: 4NEC2 plot of SuperMoxonSWRand reflection coefficient.
the bent corners in 3/8" material. 3/8" saving means of
-B- -E- -F-
- D--c-
fibreglass rod was used for the element achieving a good 'gain'
insulators both at the driven element centres
and at the element ends. The 6m antenna
antenna on the HF bands.
--G
has been tested with 1000W from an REGISTEREDDESIGN.
ACOM 1000 without complaint. (The This design is being registered
insulators on the directors on the 2m and therefore commercial
version are only 12mm long but at the manufacture is not permitted
50W power level no arcing or instability without perm ission of the design FeedpO~
A xH
was noted. Unfortunately no greater power owner. However, radio amateurs
was available on 2m for testing,) may freely construct and use
Table 1 gives constructional sizes for this antenna for their personal
6m, 4m and 2m versions, the dimensions amateur stations. Commercial
relating to Figure 5. The front part of the versions of the antenna are
driver element is of course split at the centre available from Vine Antennas
and 500 feed line connected there through Ltd [2].
a balun. J K L M
WEBSEARCH
Although the final dimensions are as set
[1] www.moxonantennaproject.com/ . FIGURE5: Basic design of the SuperMoxon.SeeTable 1
out in the table, it is useful to slit the ends of design.htm for 6m, 4m and 2m versiondimensions.
the main element tubes and install stainless [2] www.vinecom.co.uk
