Topband: 160m T-loaded vertical antenna

[Jim Brown]

On Wed, 28 May 2008 14:32:19 +0700, Jo,YC0LOW wrote:

>very grateful to hear any advises on what to do best to optimise 

Hello Jo,

We are very encouraged that you are working on your station for 
topband. When I am on the air around your sunset or my sunrise 
(currently 1250Z), I often am able to hear and work stations from 
your part of the world. 

I have an antenna similar to yours, but the vertical part is 
taller. It works quite well. I have four pieces of advice. 

First, you need MANY more radials. Radials that are only 3M off 
the ground are NOT elevated radials for 160M -- because they are 
only a tiny fraction of a wavelength above ground, they act more 
like ground-mounted radials. Follow the advice of all antenna 
books to add as many as possible, with 60 being a target. Don't 
worry about length, don't worry about direction, don't worry about 
straight. Just follow the simple rules -- more is better, and 
copper close to the antenna is more important than copper distant 
from the antenna! And feel free to put them on the ground if that 
makes it easier to install them. There is no benefit to raising 
them to 3M. (There WOULD be a benefit for a 20M antenna). 

Second, do NOT use SWR as an indicator of antenna performance. It 
is only an indicator of the impedance match. Your feedline is FAR 
too short (only 1/6 wavelength) and far too good to be worried 
about that. Any good antenna tuner in the shack will match it to 
your transmitter, and many transmitters will be happy with 1.6::1 
without a tuner. Rather, I would simply concentrate on reducing 
the ground losses (more radials). 

Third, consider eliminating the UNUN. Depending on how it is 
built, it may be contributing loss. Again, the mismatch to the 
line is too small to worry about in such a short transmission 
line, provided that you are able to match it to the transmitter 
with a tuner or the transmitter can load it. To determine if the 
UNUN is lossy, transmit for a long time, then stop transmitting 
and go feel the UNUN to see if it is hot. If it is, eliminate it. 
If it is not, it is fine to keep it. 

Fourth, you should also try to work on some sort of receiving 
antenna. You can't work what you can't hear. A Beverage or a loop 
can help a lot. There are many QSOs in my log that wouldn't be 
there if I didn't have Beverages.  

73,

Jim Brown K9YC
Santa Cruz, CA