[TowerTalk] Re: Beverage boxes

[Tom Rauch]

Hi Tom,

> For years, I worked JA's listening on my 400 ft SSE 
> unterminated Beverage.  Then I built a bi-directional 525 ft 
> antenna and found that it heard as well to the SSE as the 
> 400 ft Beverage, but I picked up 4 to 6 dB to JA, confirming 
> your predictions.

They aren't really my predictions. I first heard about that effect in a 
series of lectures in the 60's by John Kuecken at General 
Dynamics, when he was discussing long wire antennas.The F/B 
ratio of a long wire is about equal to the return loss through the 
wire, which makes complete sense.

That's also why all my longer Beverages (some up to 3 WL long) 
are now abandoned. By the time I get out 500 or 800 feet on the 
antenna, over 1/3 of the current is gone. Adding more length just 
doesn't do much for directivity because of the attenuation along the 
wire (about 3dB loss in that distance). 

If the wire is poorly terminated it helps the wire "self-terminate" and 
improves S/N, but I've found very little difference if I properly 
terminate the antennas when I compare a 500 foot Beverage and a 
1500 foot Beverage.   

Kuecken put his series of lectures into a book that was published 
by Howard W. Sams, but they dropped the book from publication. I 
convinced Martin Jue to have a few thousand copies reprinted, 
because I thought the book was worthwhile. I don't know if any 
copies are still available but the name of the book is "Antennas and 
Transmission Lines".   
 
> Most of my RX antenna feedlines all run on the ground.  
> Does that help minimize pickup?

I have no idea! It would depend on how your soil behaves. On 160 
meters, skin depth ranges from a few feet to perhaps 30 feet or 
more. 

I bury all my cables when possible but I also choke them off with 
strings of ferrite beads and ground them to ground rods before they 
reach the antennas. My Beverages have one or two six foot ground 
rods at the feedpoints, so the coax can be a major part of the 
antenna system. Without additional isolation, only the "clamping 
effect" of the ground rod would keep the coax from being part of the 
antenna!  

I don't worry when I have a good ground system at the receiving 
antenna and have the cable buried fairly deep. My receiving vertical 
arrays all have large ground screens, and cables buried at least six 
inches deep. Obviously the feedlines can't do much to affect those 
systems, because the ground system is a few ohms of impedance. 
The ground system pretty much shorts the shield out to ground.

This stuff would also be important at a multi-multi, where the 
transmitters could get into the receiving antennas and overload stuff.
73, Tom W8JI
w8ji@contesting.com

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