I made many changes to some of my noisy beverages and have dropped the
noise level by a large amount. I saw an improvement last night and this
morning of around 27 dB from where I started, which is huge in my book!
The two previously unusable beverages are now effective. Today I ran
some measurements with a vector network analyzer to get a feel for the
isolation between my 1/4 wave vertical and the beverages, which criss
cross my property. The numbers include feeder loss on both the TX and
the RX antennas.
The two noisy beverages were quite close to the vertical antenna.
After moving the wire endpoints away from the vertical, I saw the
Southwest beverage 50 ft to 150 ft separation -39.8 dB Was very
West beverage moved from 50 to about 150 ft -41.8db Was very noisy B4
290 degree beverage
330 degree beverage -58.5dB
45 degree Europe beverage -52.8dB
90 degree beverage -43.5dB* jumped around up to -52 dB..not sure why?
180 degree beverage -52.5dB
These numbers make me think that I might need more isolation on the SW
and the West beverages. One interesting factor affects the Europe
beverage. It consists of a pair of 1200 ft long wires parallel to each
other and 380 ft apart. The -52.8 dB isolation is measured with both
wires adjusted for maximum gain (in phase). The farther 45 degree
beverage showed -62 dB while the closer one was at about -52 dB. I can
vary the phase between the wires and adjust the input levels with an
NCC-1 phasing box. By tweaking the NCC-1 I could get close to -100 dB
isolation apparently by moving the sidelobes and putting a null in the
direction of the vertical radiator. I wish I had a couple of those NCC-1s!
It is snowing heavily, but as soon as the snow stops and I get things
plowed out, I will rig up a decent relay to short out the gamma match
cage feed. I made some isolation measurements on the SW beverage with
the gamma match shorted and open. Isolation went from -39.8 dB to -60.7
dB so it does help, although I could not see any change in noise whether
open or shorted. Possibly a shorted gamma connection is not a good
indicator for isolation?
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