THE RICHMOND ROCKET ANTENNA
by KB8IDW
A recent rainy Saturday afternoon brought me to 3868khz lsb, my usual hangout when not
QRP’ing. Yes, I’m a closet 75 meter QRO operator, running around 700 watts
output with my Kenwood TS940s/at and old trusty Heathkit amplifier. I’ve been hanging
out with a group of guys here for about 8 years now and see most of them once or twice a
year, either at the Richmond hamfest in January , or during field day in the deep woods of
Saluda, VA.
As usual my signal into Central and Southern Virginia from my 80 meter coaxial dipole
was anywhere from 20-30 db over s9 depending on who you asked. My friend Jim N4MXZ’s
signal was it’s usual booming 40 – 50 db over s9. Jim is an Electronic Engineer
in Richmond and an antenna design guru. It seems like every time I talk to him on 3868,
his signal is huge compared to mine. He usually runs around the legal limit while my
output is around 700 watts, so this accounts for some of the disparity in signal strength
between us, but not all of it. He is continually striving to improve his antenna system
and makes changes quite frequently. I decided to ask him to describe the antenna he was
using that day so I could build one for myself. I’ll spare you the technical
explanation provided to me by Jim as to how this antenna works and instead describe the
end product:
Basically the antenna is a little longer than twice the length of a G5RV. The
dimensions are as follows: 208ft long, center-fed with 66feet of ladder line then 100ft of
coax into the shack. The ladder line is soldered directly to the antenna at the feedpoint,
and the coax is connected to the ladder line with one of those oval shaped rubber/plastic
gizmo’s I bought at a hamfest that has an SO-239 connector on the bottom to plug the
coax in, and a place to solder each side of the ladder line to. Think about it; 50 ohm
coax hooked directly to 75 ohm ladder line, no balun, ladder line soldered directly to the
antenna. Sounds like a temporary field day antenna right? Wrong…… The day this
antenna was put up, I quickly tuned around the bands to see where the antenna was resonant
allowing operation without a tuner. I made the following non-scientific swr measurements
using my Autek WM-1 wattmeter while keying up with a couple of watts rf:
75 meters: less than 1.5:1 from 3820-3935khz
40 meters: very high swr across the entire band (at least 3 to 1)
20 meters: between 2 and 4 to 1 across the entire band.
15 meters: between 2 and 4 to 1 across the entire band
10 meters: less than 1.5:1 on several 50-75 khz segments above 28.5mhz.
This antenna may not be for everyone, but what I was looking for was a better signal on
75 meters, and I also wanted to get on 160 meters with a half decent signal. This antenna
definitely achieved my objective on 75 meters. For over three years, I consistently
received 20-30db over s9 signal reports from the guys down in Richmond (90 miles South of
here), and the guys down in the Virginia Beach area (about 160 miles south of here) using
my Coaxial dipole, and various home brew 80/75 meter antennas. Since installing this
antenna I consistently receive 30-40db over s9 signal reports from the same guys. Jim in
Richmond, used to hit me with 40-50 over signals, now he averages between 50 over and
"pegging" my needle. I like to surf the 75 meter phone band, answering loud
CQ’s that I hear. Usually I wait until well into the QSO before I tell the guy that
I’m running QRP and most of them are amazed that I’m only running 5 watts. In
the CW portion of the 80 meter band, a tuner is required, but the results I’ve gotten
have been phenomenal . The QRP’ers around 3560 always ask about my antenna. The first
evening with the antenna, I would tune in a QRP station with my 80 meter coaxial dipole
and would receive the station at around an s5 or s6, after switching to the new antenna,
their signal would jump up to a s7 to s8!!! Running QRP CW on 80 meters has never been
this fun, I feel like a big gun in that portion of the band.!
160 meters has been a pleasant surprise to say the least. For years since becoming
licensed in 1979 as KA5GVG I have occasionally tried to operate on 160 meters, usually
with the same dreary results. I would tune across the band and most of the signals were
weak, and the few that I did manage to work gave me horrible signal reports. So for the
most part, I have avoided operation on that band until now. The first evening with this
new antenna, I tuned across the bands and found strong signals everywhere. Whenever I
would find a strong signal (20 over s9 or better), I would flip the antenna switch over to
the 80 meter coaxial dipole and the signal would immediately drop to s9 or below. Now I am
working stations on 160 meter CW QRP around 1810khz and guys are usually surprised to hear
that I’m only running 5 watts. Its really fun to tune around 160 meters and get into
a SSB QSO with someone who is running the legal limit with a big 30 or 40 over s9 signal.
They probably assume I’m running barefoot (100 watts) with a marginal antenna system
until I tell them that my power output is 5 watts!!. They usually get very curious and
want me to tell them about my antenna.
Not only did this antenna achieve my objective for the low bands, but can you believe
the swr readings on the WARC bands!!!. I got more than I bargained for. The minute I
installed this antenna, I noticed BIG signal differences on 30 and 17 meters. I tuned
around the 30 meter band listening to signals from the West Coast, and Europe. Each time I
came across a signal, I would do a signal comparison using my 6 position MFJ coax switch
in the shack. The new antenna was compared against my 80 meter coaxial dipole up 50ft, a
vertically polarized 20 meter delta loop up 45 feet , a ground mounted 2-30mhz vertical,
my G5RV, and my Tri-bander up 35 feet. The ONLY time, repeat ONLY time it was beat was on
10, 15 & 20 meters when compared to my Tri-bander. This antenna has been simply
fantastic on 30 and 17 meters. It is a real treat to tune around these bands, hear a
signal, and reply to him immediately without having to tune up first ( Most hams
don’t have separate resonant antennas for the WARC bands.) I would venture to guess
that while transmitting on 30 and 17, this antenna is radiating as a Vertical, with some
energy also radiating horizontally . I do a lot of operating with this antenna with less
than 2 watts on 30 meters, and have almost filled up a logbook with 5w SSB QSO’s on
17 meters. I’m not much of a 12 meter operator, but the antenna seems to perform
exceptionally there too when compared to my other antennas.
What about the other bands???? Well, according to most of the QRP’ers I have been
working on 40 meters, this antenna is putting out a killer signal. A tuner is required to
operate on 40, but it still works great. One Sunday afternoon, I strung up a temporary 40
meter dipole up 60 feet, resonant on 7.040mhz and did some comparison tests between the
two antennas while working about half a dozen or so QRP’ers between 7035 &
7045khz, and ended up taking it down before supper time. Enough said…..Now for 20, 15
and 10 meters, I have not really done a lot of comparison tests, but the few that I have
done show the tri-bander to be light years ahead. Of course this antenna was not designed
for 10 thru 20 meters anyway. If you have the room give this antenna a try you will be
amazed!!!
73’s de Doug KB8IDW