Topband: Some guidance needed

[Craig D. Smith]

Sorry to hear about the antenna problem, Mark.  I've had some experience
with a very similar setup.

You didn't mention how much of a radial system you are using.  This will be
the primary determinant of how efficient your system will be, the feedpoint
impedance at resonance, and the effectiveness for DX operation.

I've had a CG-3000 at the base of a vertical for 4 years now.  It generally
tunes well on 80 meters and up but is VERY cantankerous on 160.  I've
occasionally gotten it to work there, but more often than not it won't.  So
I'm not surprised that you are having difficulty.  It will only work when
your antenna length is close to resonance, and even then, won't be very
repeatable or reliable.

If you are serious about 160, here is what I would recommend.  I've done it
here for 160 and it works very well.  Adjust your wire length to be resonant
at your frequency range of interest (i.e. CW or phone).  It appears you have
the space to do this.  If you need more space, just let the end of the wire
hang down vertically towards the ground.  I do this without any problem.
You will then have a resonant system, with the feedpoint impedance (mostly
all resistive) determined by your radial system and ground conductivity.
This impedance could vary from 32 ohms (perfect ground) to 70 ohms or higher
(poor radial system).  The net is you will have a 2:1 or less SWR at
resonance.  This can be handled easily by the tuner in your rig or shack as
you QSY over your range of interest.  At 160, the feedline losses due to
this SWR will be modest.

You can improve things by installing a UNUN at the base where you presently
have the CG-3000.  The transformation impedance needed will depend on your
radial system and ground conductivity.  I built a multi-tap UNUN from info
in Jerry Sevick's book.  This allows me to adjust the SWR to very close to
1:1 and operate without any tuner over a bandwidth of about 50 KHz.  If I do
need to QSY outside my normal range, I just use the internal tuner in my
rig. You can determine your feedpoint impedance by using an antenna analyzer
AT THE ANTENNA BASE.  I've used this setup in several 160 meter CW contests
with good results with 100W of power.

Another alternative, which I have not tried, is to make your wire longer
than resonance and then tune for resonance with a variable capacitor at the
base.  This eliminates some pruning of wire length at the expense of
additional complexity.  You could of course also use a L network at the base
to handle both the R and X components, but this is even more complex.
Overall, I like (and recommend) the approach of a resonant antenna in
conjunction with the UNUN.

       Good Luck and 73   Craig   AC0DS