The DBJ-2: A Portable VHF-UHF Roll-Up

J-pole Antenna for Public Service

WB6IQN reviews the theory of the dual band 2 meter / 70 cm J-pole
antenna and then makes detailed measurements of a practical, easy to
replicate, “roll-up” portable antenna.
Edison Fong, WB6IQN

It
has now been more than three tion pattern of an end-fed J-pole mounted at
years since my article on the the top of a tower is not distorted.
dual band J-pole (DBJ-1) The J-pole works by matching a low
appeared in the February 2003 impedance (50 Ω) feed line to the high
issue of QST.1 I have had over 500 inquires impedance at the end of a λ/2 vertical dipole.
regarding that antenna. Users have reported This is accomplished with a λ/4 matching
good results, and a few individuals even stub shorted at one end and open at the other.
built the antenna and confirmed the reported The impedance repeats every λ/2, or every
measurements. Several major cities are using 360° around the Smith Chart. Between the
this antenna for their schools, churches and shorted end and the high impedance end of
emergency operations center. When asked the λ/4 shorted stub, there is a point that is
why they choose the DBJ-1, the most com- close to 50 Ω and this is where the 50 Ω coax
mon answer was value. When budgets are is connected.
tight and you want a good performance-to- By experimenting, this point is found to
price ratio, the DBJ-1 (Dual Band J-pole–1) be about 11⁄4 inches from the shorted end on
is an excellent choice. 2 meters. This makes intuitive sense since
In quantity, the materials cost about $5 per 50 Ω is closer to a short than to an open cir-
antenna and what you get is a VHF/UHF base cuit. Although the Smith Chart shows that
station antenna with λ/2 vertical performance this point is slightly inductive, it is still an
on both VHF and UHF bands. If a small city excellent match to 50 Ω coax. At resonance
builds a dozen of these antennas for schools, Figure 1 — The original 2 meter ribbon the SWR is below 1.2:1. Figure 1 shows
public buildings, etc it would cost about $60. J-pole antenna. the dimensions for a 2-meter J-pole. The
Not for one, but the entire dozen! 151⁄4 inch λ/4 section serves as the quarter
Since it is constructed using PVC pipe, it radials. The DBJ-1 is easy to construct using wave matching transformer.
is UV protected and it is waterproof. To date inexpensive materials from your local hard- A commonly asked question is, “Why
I have personally constructed over 400 of ware store. For its simplicity and small size, 151⁄4 inches?” Isn’t a λ/4 at 2 meters about
these antennas for various groups and indi- the DBJ-1 offers excellent performance and 181⁄2 inches? Yes, but twinlead has a reduced
viduals and have had excellent results. One consistently outperforms a ground plane velocity factor (about 0.8) compared to air
has withstood harsh winter conditions in the antenna. and must thus be shortened by about 20%.
mountains of McCall, Idaho for four years. Its radiation pattern is close to that of an A conventional J-pole configuration
The most common request from users ideal vertical dipole because it is end-fed, works well because there is decoupling of
is for a portable “roll-up” version of this with virtually no distortion of the radiation the feed line from the λ/2 radiator element
antenna for backpacking or emergency use. pattern due to the feed line. A vertically since the feed line is in line with the radiat-
To address this request, I will describe how polarized, center-fed dipole will always have ing λ/2 element. Thus, pattern distortion is
the principles of the DBJ-1 can be extended some distortion of its pattern because the minimized. But this only describes a single
to a portable roll-up antenna. Since it is the feed line comes out at its center, even when a band VHF J-pole. How do we make this into
second version of this antenna, I call it the balun is used. A vertically polarized, center- a dual band J-pole?
DBJ-2. fed antenna is also physically more difficult
to construct because of that feed line coming Adding a Second Band to the
Principles of the DBJ-1 out horizontally from the center. J-pole
The earlier DBJ-1 is based on the J-pole,2 The basic J-pole antenna is a half-wave To incorporate UHF coverage into a VHF
shown in Figure 1. Unlike the popular vertical configuration. Unlike a vertical J-pole requires some explanation. (A more
ground plane antenna, it doesn’t need ground dipole, which because of its center feed is detailed explanation is given in my February
usually mounted alongside a tower or some 2003 QST article.) First, a 2 meter antenna
1Notes appear on page 40. kind of metal supporting structure, the radia- does resonate at UHF. The key word here is
From March 2007 QST © ARRL
 Figure 4 — The dual-
band J-pole modified
for portable operation
— thus becoming
the DBJ-2. Note that
the dimensions are
slightly longer than
those in Figure 3
because it is not
Figure 2 — Elevation plane pattern enclosed in a PVC
comparing 2 meter J-pole on fundamental dielectric tube.
and on third harmonic frequency (70 cm), Please remember that
with the antenna mounted 8 feet above the exact dimensions
ground. Most of the energy at the third vary with the manu-
harmonic is launched at 44º. facturer of the 300 Ω
line, especially the
exact tap point where
the RG-174A feed
coax for the radio is
connected.

Figure 5 — The λ/4 UHF decoupling stub made of RG-174A, covered with heat shrink
tubing. This is shown next to the BNC connector that goes to the transceiver.

Figure 3 — The original DBJ-1 dual-band used in a vertical configuration, as in the Refer to Figure 3, and start from the
J-pole. The dimensions given assume that J pole shown in Figure 1. This can be best left hand bottom. Proceed vertically to the
the antenna is inserted into a 3⁄4 inch Class explained by a 19 inch 2 meter vertical over RG-174A lead in cable. To connect to the
200 PVC pipe.
an ideal ground plane. At 2 meters, it is a λ/4 antenna, about 5 feet of RG-174A was used
length vertical (approximately 18 inches). with a BNC connector on the other end. The
At UHF (450 MHz) it is a 3λ/4 vertical. λ/4 VHF impedance transformer is made
resonate. For example, any LC circuit can Unfortunately, the additional λ/2 at UHF is from 300 Ω twin lead. Its approximate
be resonant, but that does not imply that it out of phase with the bottom λ/4. This means length is 15 inches due to the velocity fac-
works well as an antenna. Resonating is one cancellation occurs in the radiation pattern tor of the 300 Ω material. The λ/4 piece is
thing; working well as an antenna is another. and the majority of the energy is launched at shorted at the bottom and thus is an open
You should understand that a λ/4 146 MHz a takeoff angle of 45°. This results in about circuit (high impedance) at the end of the λ/4
matching stub works as a 3λ/4 match- a 4 to 6 dB loss in the horizontal plane com- section. This matches well to the λ/2 radiator
ing stub at 450 MHz, except for the small pared to a conventional λ/4 vertical placed for VHF. The 50 Ω tap is about 11⁄4 inches
amount of extra transmission line losses of over a ground plane. A horizontal radiation from the short, as mentioned before.
the extra λ/2 at UHF. The UHF signal is pattern obtained from EZNEC is shown in For UHF operation, the λ/4 matching
simply taking one more revolution around Figure 2. Notice that the 3λ/4 radiator has stub at VHF is now a 3λ/4 matching stub.
the Smith Chart. most of its energy at 45°. This is electrically a λ/4 stub with an addi-
The uniqueness of the DBJ-1 concept Thus, although an antenna can be made tional λ/2 in series. Since the purpose of the
is that it not only resonates on both bands to work at its third harmonic, its perfor- matching stub is for impedance matching
but also actually performs as a λ/2 radiator mance is poor. What we need is a simple, and not for radiation, it does not directly
on both bands. An interesting fact to note reliable method to decouple the remaining affect the radiation efficiency of the antenna.
is that almost all antennas will resonate at λ/2 at UHF of a 2 meter radiator, but have It does, however, suffer some transmission
their third harmonic (it will resonate on any it remain electrically unaffected at VHF. We loss from the additional λ/2, which would
odd harmonic 3, 5, 7, etc). This is why a want independent λ/2 radiators at both VHF not be needed if it were not for the dual
40 meter dipole can be used on 15 meters. and UHF frequencies. The original DBJ-1 band operation. I estimate this loss at about
The difference is that the performance at the used a combination of coaxial stubs and 0.1 dB. Next comes the λ/2 radiating ele-
third harmonic is poor when the antenna is 300 Ω twinlead cable, as shown in Figure 3. ment for UHF, which is about 12 inches. To
From March 2007 QST © ARRL
 Table 1 Table 2
Measured Relative Performance of the Dual-band Measured Relative Performance of the Dual-band
Antenna at 146 MHz Antenna at 445 MHz
VHF Flexible Standard Dual-Band UHF Fexible Standard Dual-Band
VHF λ/4 GP Antenna VHF J-Pole J-Pole UHF λ/4 GP Antenna VHF J-Pole J-Pole
4 radials 4 radials
0 dB −5.9 dB +1.2 dB +1.2 dB 0 dB −2.0 dB −5.5 dB 0.5 dB
reference reference

make it electrically terminate at 12 inches, a I used heat shrink tubing to cover and pro- is significant. I have confidence in these
λ/4 shorted stub at UHF is constructed using tect the UHF λ/4 decoupling stub and the measurements since the flexible antenna is
RG-174A. The open end is then connected four 1⁄4 inch notches. Similarly, I protected about −6 dB from that of the λ/4 ground
to the end of the 12 inches of 300 Ω twin- with heat shrink tubing the RG-174A coax plane antenna, which agrees well with the
lead. The open circuit of this λ/4 coax is onlyinterface to the 300 Ω twinlead. I also literature.
valid at UHF. Also, notice that it is 41⁄2 inches
attached a small Teflon tie strap to the top Also notice that at UHF, the loss for the
and not 6 inches due to the velocity factor of of the antenna so that it may be conveniently flex antenna is only 2.0 dB, compared to the
RG-174A, which is about 0.6. attached to a nonconductive support string. ground plane. This is because the flexible
At the shorted end of the 4 1⁄ 2 inch Figure 5 shows a picture of the λ/4 UHF antenna at UHF is already 6 inches long,
RG-174A is the final 18 inches of 300 Ω matching stub inside the heat shrink tubing. which is a quarter wave. So the major differ-
twinlead. Thus the 12 inches for the UHF The DBJ-2 can easily fit inside a pouch or a ence for the flexible antenna at UHF is the
λ/2, the 41⁄2 inches of RG-174A for the large pocket. It is far less complex than what lack of ground radials.
decoupling stub at UHF, and the 18 inches would be needed for a single band ground
of twinlead provide for the λ/2 at 2 meters. plane, yet this antenna will consistently out- Summary
The total does not add up to a full 36 inches perform a ground plane using 3 or 4 radials. I presented how to construct a portable,
that you might think. This is because the Setup time is less than a minute. roll-up dual-band J-pole. I’ve discussed its
λ/4 UHF RG-174A shorted stub is induc- I’ve constructed more than a hundred basic theory of operation, and have presented
tive at 2 meters, thus slightly shortening the of these antennas. The top of the DBJ-2 is experimental results comparing the DBJ-2
antenna. a high impedance point, so objects (even if to a standard ground plane, a traditional
they are nonmetallic) must be as far away 2 meter J-pole and a flexible antenna. The
Making it Portable as possible for best performance. The other DBJ-2 antenna is easy to construct, is low
The single most common question that sensitive points are the open end of the λ/4 cost and is very compact. It should be
people asked regarding the DBJ-1 is how it VHF matching section and the open end of an asset for ARES applications. It offers
could be made portable. The original DBJ-1 the λ/4 UHF decoupling stub. significant improvement in both the VHF
had the antenna inserted into Class 200 PVC As with any antenna, it works best as and UHF bands compared to the stock flex-
pipe that was 6 feet long. This was fine for high as possible and in the clear. To hoist the ible antenna antenna included with a hand-
fixed operation but would hardly be suitable antenna, use non-conducting string. Fishing held transceiver.
for portable use. Basically the new antenna line also works well. If you do not have the equipment to
had to have the ability to be rolled up when construct or tune this antenna at both VHF
not in use and had to be durable enough for Measured Results and UHF, the antenna is available from the
use in emergency communications. I measured the DBJ-2 in an open field author tuned to your desired frequency. Cost
The challenge was to transfer the concepts using an Advantest R3361 Spectrum is $20. E-mail him for details.
developed for the DBJ-1 and apply them to Analyzer. The results are shown in Table 1.
Notes
a durable roll-up portable antenna. After The antenna gives a 7 dB improvement over 1E. Fong, “The DBJ-1: A VHF-UHF Dual-Band
much thought and experimenting, I adopted a flexible antenna at VHF. In actual practice, J-Pole,” QST, Feb 2003, pp 38-40.
2J. Reynante, “An Easy Dual-Band VHF/UHF
the configuration shown in Figure 4. since the antenna can be mounted higher
Antenna,” QST, Sep 1994, pp 61-62.
The major challenge was keeping the than the flexible antenna at the end of your
electrical characteristics the same as the handheld, results of +10 dB are not uncom-
original DBJ-1 but physically constructing mon. This is the electrical equivalent of giv- Ed Fong was first licensed in 1968 as WN6IQN.
it from a continuous piece of 300 Ω twin- ing a 4 W handheld a boost to 40 W. He later upgraded to Amateur Extra class
lead. Any full splices on the twinlead would The DBJ-2 performs as predicted on with his present call of WB6IQN. He obtained
compromise the durability, so to electrically 2 meters. It basically has the same perfor- BSEE and MSEE degrees from the University
disconnect sections of the twinlead, I cut mance as a single band J-pole, which gives of California at Berkeley and his PhD from the
small 1⁄4 inch notches to achieve the proper about a 1 dB improvement over a λ/4 ground University of San Francisco. A Senior Member
resonances. I left the insulating backbone plane antenna. There is no measurable of the IEEE, he has 8 patents, 24 published
of the 300 Ω twinlead fully intact. I deter- degradation in performance by incorporat- papers and a book in the area of communica-
tions and integrated circuit design. Presently,
mined the two notches close to the λ/4 UHF ing the UHF capability into a conventional
he is employed by the University of California
decoupling stub by experiment to give the J-pole. at Berkeley teaching graduate classes in RF
best SWR and bandwidth. The DBJ-2’s improved performance design and is a Principal Engineer at National
Because this antenna does not sit inside is apparent at UHF, where it outperforms Semiconductor, Santa Clara, California working
a dielectric PVC tube, the dimensions are the single band 2 meter J-pole operating with CMOS analog circuits. You can reach the
about 5% longer than the original DBJ-1. at UHF by about 6 dB. See Table 2. This author at edison_fong@hotmail.com.
From March 2007 QST © ARRL
 Building an Emergency J-Pole
By Phil Karras, KE3FL
June 15, 1999

This type of J-Pole has been written about in QST, and the description has
appeared elsewhere (see "Bibliography," below). The J-Pole is not difficult to
make, even for a beginner. This antenna works well on 2-meters; it also works
on 440 MHz.

If you look at the antenna, it is a 3/4- Some Past J-Pole Articles in QST:
wavelength radiating section attached to the
matching stub by the shorting bar; all together • QST Jul 1995, p 62, "Build a
it looks like the letter J, hence the name J-pole. Weatherproof PVC J-Pole Antenna,"
• QST Jun 1995, p 71, "Try A 2-Meter
Read all of these instructions before beginning Flexi-J Antenna"
your construction project. Nothing is more • QST Sep 1994, p 61, "An Easy Dual-Band
frustrating than doing something, only to find a VHF/UHF Antenna"
hint afterwards that would have made the • QST Apr 1982, p 43, (This was the article
project go smoother. for a wire J-pole antenna I was able to
find in QST).
See below for a listing of parts and tools you'll
need to make up this simple antenna.

Larger picture available here.

Using "ladder line" is a bit different than using solid-dielectric TV twinlead. Before cutting,
stretch out the wire so that you can position the proposed cuts at a position that has a center
plastic support, and not at a position that has no center plastic. This may not be possible for both
the 1/4-wavelength section and the total length position. If it comes down to a choice, I
recommend selecting the support at the top.

This plastic melts well and can be melted back together. I have had to melt sections back
together in both locations, and the antennas work just fine and hold up to field rigors.
Select the bottom of the antenna and strip off about 3 to 3-1/2 inches of insulation from both
wires. Tack solder (temporary solder joint) a piece of wire as a shorting bar about 1 inch from the
bottom of the antenna (this bar may need to be moved).

To start with, the coax will be connected about 1-1/4 inch from the shorting bar. This connection
and the shorting bar connection may need to be moved in order to achieve the best SWR and
frequency match.

Measure 17 inches up from the shorting bar on one end only and cut a 1/4-inch gap in the wire at
this position. (You can melt the plastic back together at this location if needed.)

Now measure 52-1/4 inches up from the shorting bar. If this location has no center plastic
support, try to remove as little insulation as needed in order to get at the wire and snip it. Cut
out at least one inch of wire, then melt the plastic back onto the locations where you removed it.

I use a sharp knife to cut into the insulation and not into the wire. Then I pry the wire out with a
pin and snip it or solder it at the correct location.

Preparing the Coax

Bend the coax about an inch from the end, and score the insulation with a sharp knife. This cuts
into the insulation without damaging the shield if done gently. Then rotate the coax so you can
continue scoring the coax until it is cut all the way around. Cut the insulation from the new cut,
up to the end of the coax. You should now be able to pull off the insulation with pliers.

Remember to always cut away from yourself!

Never use wire strippers on the large portion of the coax; it only damages the shield. If you have
a tool designed for coax, use it.

Prepare the antenna end of the coax: Separate the coax shield and twist it together. Strip off
about 3/4-inch of insulation from the center conductor of the coax. (Do not solder at this time.)

You'll install the appropriate connector (BNC, PL-259) at the other end of the coax. Follow the
installation directions that come with the connector, or consult The ARRL Handbook for more
information.

Connecting Coax to Antenna

Wrap the shield 1-1/4 inch up from the shorting bar around the 17-inch side of the twin lead.
Wrap it in such a way that the distance from the coax to the shorting bar is the same for both the
shield and the center conductor. Solder the shield to the twin lead.

Wrap the center coax conductor around the longer twin lead wire up from the shorting bar (the
same distance that the shield is wrapped to the other wire) and solder it.

Cut off the excess coax wire. Also, cut off all the excess twin lead at the top except for a loop or
two. These ladder steps are great for hanging the antenna over a nail or hook, so leave at least
one of them.
Your antenna is now ready to test.

Testing Your J-Pole

Get your VHF SWR analyzer or meter. Hang the antenna away from all objects (I hang mine
from the top of a window and this seems to work almost as well as from a tree).

For best SWR measurements, the antenna should be at least 2 wavelengths away from any
object. (For 2-meters this is approximately 13 feet.)

Set your radio for lowest power and 146.000 MHz simplex. Test out the antenna for 144.000 and
148.000 as well. If all three are below 1.7 SWR and the SWR for 146 is about 1.3 or lower, you
are done. If not, see for the sidebar "Help for Lowering the SWR, Changing the Frequency, and
Increasing the Bandwidth" below.

Once you are done, slip the shrink tubing onto the antenna over the coax connections, squirt
some electrical-connection safe RTV into the bottom of the shrink tubing, and then heat up the
tubing from the bottom up. This should push (squeeze) some RTV all the way to the top of the
shrink tubing. Wipe off the excess and hang the antenna for 12 to 24 hours to let the RTV dry.

The SWR at 146.0 should be close to and below 1.3 to 1; for 144.0 and 148.0, it should be 1.7 to 1
or lower. If you have difficulty obtaining these results, see "Help for Lowering the SWR,
Changing the Frequency, and Increasing the Bandwidth", below.

At 445.0 MHz, the antenna should read below 1.5 to 1. I have not checked it out as thoroughly as
I have 2 meters, but I do know that it is not a nice one-dip curve; rather, it is a multiple dip/peak
curve.

Editor's note: Philip Karras, KE3FL, lives in Mt Airy, Maryland. An ARRL Life Member, he
holds a field appointment as Assistant Emergency Coordinator in Carroll County, Maryland. He's
also an OES, ORS, and a volunteer examiner. He may be contacted via e-mail to ke3fl@arrl.net.
Visit his Web site at http://www.qsl.net/ke3fl.

PARTS LIST:

5 feet of 450-ohm ladder line

20 feet of RG-58 or similar coax
2 inches of heat-shrinkable tubing

NECESSARY TOOLS:

Soldering iron (20-30 W)

Solder
Wire cutters
Wire strippers
VHF SWR meter or antenna analyzer
Sharp knife
Pliers
RTV silicone sealant
Heat gun or hair dryer (for heat-shrinkable tubing)
Help for Lowering the SWR, Changing the Frequency, and Increasing the Bandwidth

If your antenna did not have a nice low SWR at the desired center frequency, try moving the
shorting bar down about 0.1 inch at a time until you get the lowest SWR you can--even if this is
nowhere close to 1:1. You may have to move it back up if you go too far. Normally I find that I
have to move the shorting bar down, ie, away from the feed-point, but it's always possible that it
will need to go the other way too.

If you have already cut the extra wire off the bottom of the antenna, you will need to add some
back if moving the shorting bar closer to the feed-point only makes the SWR worse. Add about
two inches to both the matching stub and radiator at the bottom of the antenna.

Once the position of the shorting bar to the feed point that produces the lowest SWR has been
found, move the coax contact points and the shorting bar together until you can get this lowest
SWR match at the desired frequency. The important point to remember here is that the distance
between the feed-point and the shorting bar determines the lowest SWR. This distance must not
change while trying to get the lowest SWR at the desired center frequency.

If the lowest SWR you can get by moving the shorting is not 1:1, it will turn out to be closer to 1:1
once you move both the shorting bar and the coax feed point so that the lowest SWR is at the
desired center frequency.

Help on Shifting the Frequency

If you need to shift the frequency and moving the tap point doesn't change it enough, you can cut
the J-Pole. You should not have to do this for this antenna since the dimensions for this antenna
have been worked out over years of experience by many different people.

Here are the two rules of thumb for changing the center frequency of any antenna:

LLL: Longer antenna = Longer wavelength = Lower frequency

SSH: Shorter antenna = Shorter wavelength = Higher frequency

When cutting the antenna shorter, I recommend making only one-half the change you calculate.
In this way you may be able to prevent making too large a cut and having to undo it.

All changes are interactive, some more so than others, but expect to see SWR changes for length
changes, and frequency shifts when moving the shorting bar/feed-point up and down. (Remember
to move both the feed-point and the shorting bar in tandem, keeping the distance between them
constant when trying to re-center the lowest SWR at the frequency you want.)

Help on Increasing the Bandwidth (BW)

Once again you should not ever have this problem with the 2-meter J-pole since the dimensions
have been worked out by calculation and by trial and error by many people. However, if you are
trying to design for a new frequency, you might need to be able to change the BW.

A very narrow BW may be an indication that the radiator is too long, or it is too long in relation
to the matching stub. I have only performed one experiment so far. In this experiment I added
one inch of wire to the top of a good working J-pole antenna for 2-meters. The bandwidth
dropped to about 0.6 MHz. When I removed the extra wire, the BW returned to about 3.8 MHz
between 1.7:1 SWR points.

Other things I've tried made such small changes in the bandwidth that I was never sure the data
was significant. Was the change due to the method tried or did I do something else a bit
differently that caused the change?

 
 February 1995 QST Volume 79, Number 2

way is to obtain the angle of declination from a topographic map. Often referred to as the variation angle in air and sea
navigation, this angle is simply the difference between true and magnetic North at a specified location. By knowing this
angle, you can correct your compass reading for true North.
You can learn more about coordinates, great-circle headings, topographic maps and associated computer programs
by reading the “Lab Notes” column in the April 1994 QST.
Q: I’m getting terrible interference to my VHF transceiver from my computer. Is this interference coming directly from the
CPU?
A: It’s rare to have interference directly from the CPU, but it is possible. Most computer interference is radiated by the
wiring, primarily between peripheral devices (printers, modems, joysticks and so on). High-quality shielded cables are a
good start toward solving this problem. Wrapping the cables though large toroids such as the FT-240-61 may also help.
Consider the shielding on your computer, too. The quality and amount of shielding can vary considerably. The better
computers have metal cabinet covers that must be removed if you want to replace or add any components. Some hams
have even gone to the trouble of lining their computer cabinets with metal foil!
Q: I built the dual-band J-pole antenna from the article in the September 1994 New Ham Companion (“An Easy Dual-Band
VHF/UHF Antenna,” page 61), but I just can’t get it to work. What can I do?
A: Try adding a balun to the coax. A balun is necessary because a J-pole antenna uses a balanced feed (the
1/4-wavelength matching section) connected to an unbalanced feed line (the coax). The simplest way to make a balun is
to get a split-core cylindrical ferrite (such as an Amidon 2X-43-251) and attach it to the outside of the coax 1/4 wavelength
from the feedpoint. On VHF frequencies some ferrite materials are not effective, so be sure to get type 43 material for best
results.
Another thing you may want to do is lengthen the antenna a bit. The formula for the antenna length in the article is
unintentionally misleading. Because the 1/2-wavelength radiator is not a feed line, it has a much higher velocity factor than
that of twin lead. The velocity factor of copper wire is about 0.95, so the 1/2-wave radiator section should be 38-3/8 inches
long.
Q: Harvey Zion, KI7EG, asks, “One of our local club membersa fellow with a General licensewants to provide a
gateway from our VHF packet network to the 20-meter packet subband. What if a Technician on 2 meters uses the
gateway to reach 20 meters. Would that be legal?”
A: Yes, the Technician can legally use the gateway. The Technician is the control operator of his or her 2-meter station
only. The gateway is a separate station operating under the privileges of its licensee and/or control operator. This same
situation applies to repeaters with outputs on frequencies for which a user may not have privileges, as long as the user
can legally operate on the input frequency. (Two-meter to 10-meter FM repeaters are good examples.)
The 20-meter gateway raises other questions, however. Such a system is legal only if a control operator is present at
the station’s control point. Remote control is okay, but it must be via a wire line, or take place on a frequency above
222.15 MHz.
No station operating below 50 MHz can be automatically controlled with the following exceptions:
ο Repeaters operating above 29.5 MHz
ο The 50 packet stations that have been granted Special Temporary Authorization (STA) for HF packet forwarding.
ο Beacons operating between 28.2 and 28.3 MHz.
ο The NCDXF beacon system on 14.1 MHz.
Some stations have set up automatic digital mailboxes on HF, but these are not legal at the present time. There is a
rule change under consideration by the FCC that will permit limited automatic digital operation on some HF frequencies.
Watch future issues of QST for more information.
Q: Scott Long, WD8NSD, asks, “I have an unusual interference problem; my television is interfering with me! I hear a
strong signal on 3.58 MHz every time I hook my TV up to an outside antenna. This is my favorite 80-meter frequency.

Page 18 - Copyright © 1996 American Radio Relay League, Inc. All rights reserved
VK5AH 4 Bander Page 8 of 9

Back to Contents

http://users.picknowl.com.au/~wavetel/antennas.htm 10/16/2007