Maybe someone can put together a web page with examples of successful gamma
match configurations for towers.
Here is what I found this weekend with my new tower.
Tower height - 97 feet.
Top loading - 10 foot mast and essentially a 34 foot 3" boom at 98 feet.
This is my Steppir with all of the elements retracted.
Gamma match - attached at 47 feet - made out of a piece of RG8 with the
center/shield connected together. Spaced about 18 inches away from the
tower.
Capacitor value - something around 400 pf.
Radials: Currently 11 radials - most are around 1/4 wavelength of slightly
longer
At first - I had an SWR around 2.3:1 around 2.3 MHz - but using my variable
capacitor - increased the capacitance and quickly got to a perfect match
around 1800 kHz. Guess there are not any AM broadcast stations near me as
my MFJ-259B seemed quite happy.
I replaced the variable cap with a home made cap using RG8. I had one
laying around from a previous installation that looked "about right"
(length was 10 feet or more) and special treatment at the end of the
capacitor to keep it from flashing over (involving a larger ceramic guy
insulator). This also yielded a perfect mach and I went with that.
Testing with high power this morning didn't show any arcing and the matched
was stable.
The bandwidth seems very broad (maybe somewhat due to the low number of
radials) - however, this does remind me of the first gamma match I did some
32 years ago on a different tower which might have a similar electrical
length as this one. It gets up to about 2:1 at 2 MHz.
We'll see what happens as I continue to add radials. Goal is to get to at
least 40 eventually. The ground here is possible very good... totally
clay - with no rocks to be found and lots of rain during the winter (57
inches average annual rainfall).
The RX 4 square is physically up and will be QRV soon. Was able to get it
a good distance from the TX antenna but still on top of the hilltop.
Will appreciate any signal reports during the PreStew. This is the first
time I have had an antenna like this on a hilltop and I am curious how it
compares to being in the flats. I have a 600 foot drop-off over about a
mile distance in the important directions.
A quick CQ 5 minutes after sunrise this morning didn't yield any far away
RBS spots other than VE6/VE7.
Tree N6TR / K7RAT
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