I decided to take down my inv-L that was hanging beside my 72 ft Trylon tower
and try to gamma feed the tower. (The L also interfered with a sidemounted
antenna!). To keep the L out of the path of the sidemounted antenna, I tried
moving the L closer to the tower (it was about 5 ft away). But as I got closer
the real part of the impedance went upwards of 100 ohms (according to my
MFJ-259B).
I got the gamma feed working last night, but I'm surprised at the bandwidth.
Its around
260 kHz!!! I was expecting something much sharper.
----- DETAILS -----
Gamma wire: #14 stranded copper. 4ft spacing. 48ft tall.
Feed: 235pf series cap (2 470's in series)
Tower: 72 ft self supporting - face width: 4ft at base - 18" at top
Antennas: 5el 10m beam at 50ft. 24 ft boom. grounded elements.
F-12 20/40m beam at 73 ft. 30 ft boom. insulated elements.
F-12 15m beam at 84 ft. 24 ft boom. insulated elements.
Ground: 45 radials ranging from 20 to 130 ft.
Feedlines: Attach to tower at 30ft level, then slopes off to house 30 ft away.
I added a horizontal wire (50 ft long over to a tree in the yard) to the top of
the
tower (70 ft level) so that I would have some high angle radiation like the L.
SWR dips at about 1.1:1 at 1900. 2:1 at 2000 & 1740.
Without the horizontal wire, the SWR still dipped at about 1900, but with a
1.4:1
match.
I was able to work HI8 last night with 100 watts and a few calls. I heard a
few US
stations working into Europe, but I couldn't hear the EU stations.
So what do you think??? Is the antenna really that broad, or do I have a lot
of loss
in the ground system (I'm planning on adding more radials anyway).
Are conditions on 160 much worse than last year??? Last year I was able to
work into
EU fairly easily with the inv-L and 4 elevated radials.
Any other ideas for improving the system????
73
--Lee - KT4ZX
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