Topband: Question abt gain in bi- vs uni-directional Beverage

[Tom Rauch]

> I have had success in the past with 300- to 350-foot beverages. I started
> with a 390-ohm termination, but did not get good f/b until I paralleled
> another 390 ohms with it to get under 200 ohms. One of them worked best
> with the far end connected directly to the ground rod -- a termination
> equal to conductor and ground losses. 

In addition to what Gary said, you can add loading inductors 
periodically along the antenna. The Zo of the antenna increases 
(requiring a termination higher than 1000 ohms generally) and the 
pattern is very similar to a much longer Beverage.

The loads need to be every 1/8 wl or less, and the value adjusted 
so Vp is .5 freespace with a 1/2 wl wire. You could do that on a 
modeling program.

This method gives the best pattern in a short antenna. If you use 
too much inductance, the pattern reverses and isn't as good.

73, Tom W8JI
w8ji@contesting.com


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