Topband: excessive noise on beverages

[David Olean]

  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 
following isolation:

Southwest beverage 50 ft to 150 ft separation      -39.8 dB  Was very 
noisy B4

West beverage   moved from 50 to about 150 ft    -41.8db   Was very noisy B4

290 degree beverage                                                    
-56.4 dB

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?

73

Dave K1WHS