Looking for advice (plus providing an update to the reflector). A
month or so ago I reported that I was able to load my 64-foot Trylon tower
on 160M. Well, at the time all that meant was that I was able to get the
TS570 to load into it through a series cap to the shunt wire cage (three
parallel wires from ground level up to 61 feet.) The MFJ 259 analyzer goes
haywire on me around here on Topband.
Today I borrowed an MFJ731 analyzer filter for my MFJ 259 to show me
what's REALLY going on. Apparently the low SWR point (1.2:1) is around 1779
kHz and it rises smoothly to 2:1 around 1860 kHz. (It's about 1.7:1 around
1835 kHz.) My conclusion is that the shunt wires are tapped too high up on
the tower. I base this conclusion on info contained in ON4UN's book about
gamma and omega matching tall (~90 degrees electrical length) and very tall
(>130 degrees electrical length) towers. John writes that for wide gamma
wires (my cage is 18 inches wide two feet off the tower face), the tap ought
to be around 40 or so feet. (His book is in the upstairs reading room and
I'm too tired to get it now. But I can, if someone needs specific
My questions to you-all:
1. Am I correct in my conclusion (tap point is too high)?
2. Does 40 feet sound about right for the correct tap point? (Essentially
this is a gamma match arrangement.)
3. Did I supply you with sufficient info to answer the above?
4. Should I not bother changing anything and keeping the match as-is?
(Remember the story about low SWR being fatal?) Reports from domestic
stations are all 59 or better, with 100W.
Thanks for any insight you might send my way.
Gene Smar AD3F
P.S. The tower is about 5dB better, TX and RX, than my inverted L.
P.P.S. Next project is an inverted-feed ground plane for 80M on the tower
a'la N4KG. (Ain't towers fun?!)
Where do you get ICE bandpass filters & beverage matching boxes? The
same place that pays for the hosting of this list: The eHam Store.
Order online at http://store.eham.net.
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