Topband: Shorty Beverages

[Larry Molitor]

After reading the tech notes on K9AY and W8JI web sites, I decided to 
revisit the short Beverage. In the past, my shorty Beverage lengths were 
always determined by the property lines rather than science. Performance 
was always very poor. This time I would do it "by the book".

After much measuring and pacing, I found exactly one place where I could 
run a 270 foot wire without going through the house windows or tower legs. 
I wound up with a 270 foot run, 30 inches above ground, and pointing SSE.

The termination resistance was first determined by using a pot and 
adjusting for minimum signal off the back from a local AM BC station. With 
900 ohms I was able to get about 23 dB F/B. When replacing the pot with a 
fixed carbon comp resistor of the same value, that unexpectedly dropped to 
about 12 dB. An attempt to measure the surge impedance resulted in a value 
of 450 ohms. With all the 50 KW AM BC stations in the area, that 
measurement is somewhat suspect, but none the less, about what you would 
expect. With 450 ohms for the termination, F/B on the AM station was only 6 dB.

The contest gave me a chance to really see what this wire would do, or not 
do, as it turned out. With either value of termination resistance, there 
was little or no F/B on sky wave signals. While it was somewhat better than 
the TX antenna, it was not quite as good overall as the small loop and way 
behind the rotatable flag I normally use. The pattern appeared to be 
roughly a figure 8 instead of the expected cardioid.

By the way, ground resistance between ends appears to be on the order of 
100 ohms or so and there seems to be no coupling/re-radiation from the TX 
antenna. A isolation transformer was used, and beads were placed on the 
coax as an after thought with no effect.

Any one with short Beverage experience have an idea why it does not work as 
expected?

Thanks & 73,

Larry - W7IUV