Topband: Beverage coax

[Tom Rauch]

> There appears to be several flavors of RG-6, the heaviest and most
> cost is one claiming extra shielding. (quad shielding?)   The price
> looks ok even for the extra shielding at 60$/500 ft.
> My understanding is better shielding is less likely to effect the
> beverage pattern.

Hi Bob, 

The shield is the least of things affecting coax radiation problems 
on HF through upper VHF. Thick multiple-shields can be a good 
thing because they can take a lightning hit with less worry about 
opening up the cable shield, but forget about signal ingress 
problems from poor shielding unless the cable is incredibly poor. 
The general rule of thumb is if you strip the cable back and can't 
see the cable's internal dielectric looking through the shield, it is a 
good enough shield!    

Most concerns in cable selection are related to mechanical and life 
worries. Flooded cables should be used for all underground wiring, 
wiring that lays in wet areas, or wiring that rodents and animals 
might chew. Other than than problem and loss concerns, one cable 
is about as good as another.

The biggest problem by far with interaction and signal ingress are 
common mode currents, and that depends on connections at the 
ends of the cable and how the feedpoint is arranged.

Do not route the cable  parallel to the antenna and close to the 
antenna. Use an isolation-type matching transformer at the 
antenna. Don't worry about Faraday shields and other things in the 
transformer, they are for the most part useless. Just use a straight 
primary/secondary-type transformer using the correct core material 
(73 material works about best in this application). 

You can ground the cable to a separate ground rod several feet 
from the antenna (I usually don't bother, since my cables are all 
buried), but never ground it to the same ground as the Beverage 
feedpoint.

73, Tom W8JI
W8JI@contesting.com