Topband: Noise Radiation from Long Cables

[GEORGE WALLNER]

I made an observation about noise that may be of some 
value in fighting noise. I was operating the CQ 160m 
contest from a remote island in the Bahamas with very low 
ambient noise (as C6AGU). I had a Honda 1.5 kW generator 
to charge a set of batteries to power the rig. The first 
night I had my vertical located way down the beach in two 
feet of water. The operating tent was at the upper edge of 
the beach, about 150 feet to the east of the antenna. The 
generator was located about 200 feet south of the tent. 
The AC power cable was laid on the ground in more or less 
a straight line. There was one ground rod at the operating 
position and one at the antenna base. There was no AC 
filtering. The power cable from the generator to the tent 
and the coax from the tent to the antenna formed a 90 
degree angle. With this configuration there was no trace 
of generator noise on the vertical. (Which was also my 
receiving antenna.)  During the early morning large waves 
from a storm demolished the vertical. I rebuilt it during 
day further up the beach about 200 feet north of the tent. 
The coax going to the antenna now formed a straight line 
with the power cable. Strong generator noise was now on 
the vertical, which took a lot of filtering to get rid of. 
Improving the ground at the base of the vertical did not 
help. It appears that being in line with the power cable 
the antenna was picking up generator noise, which it did 
not hear when it was not in line with the cable. I 
speculate that the power cable essentially acted as BOG, 
radiating the generator noise in a direction in which it 
was laying (and probably its back-end). Indeed, one could 
speculate that any long cable lying on the ground (or in 
the air) that carried common mode noise, but would also 
radiate that noise, just like a beverage would. (Yes, 
beverage antennas do radiate, albeit not efficiently.) It 
may also be that a straight run of coax, unless it is 
buried and/or very well filtered, may not be the best way 
to feed a receiving antenna. I will do some more testing 
and provide an update later.

George
AA7JV