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[Towertalk] Snake Antennas

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Subject: [Towertalk] Snake Antennas
From: (Tom Rauch)
Date: Mon, 17 Jun 2002 05:27:02 -0400
> I thought the snake was make from coax shorted at the far end.  I know
> the articles I saw on them before, they were made from a piece of coax
> laying on the ground.  You have to be careful what length to use tho,
> cause if you get the wrong length with a short at the end, it's just
> like shorting your antenna terminals.  73 Tom W7WHY

Hi Tom,

The way coaxial cable and radio signals work, the snake really 
behaves as a random wire laid on the ground.

There is a lot of arm-waving theoretical baffle-gab about shields and 
radio signals, such as that a shield somehow prevents electrical 
interference or noise from penetrating while allowing "good" radio 
signals to reach the center conductor, but that isn't true at all.

The shield is actually the antenna that picks up signals, and that 
includes noise as well as desired signals (just as in a small 
"shielded loop").

The signal the shield "gathers up" is coupled to the center conductor 
inside the cable because the cable is intentionally connected wrong. 
The action or mechanism is the same as occurs if we connected a 
dipole to a coaxial line without a balun, and picked a length that 
encourages common-mode currents on the shield. It is also similar to 
the action in a small shielded loop, where the intentional cut in the 
shield allows the signal (and electric noise) picked up by the shield 
to spill over to the wire inside, where it eventually works it way 
back to the receiver. 

So what you wind up with, despite all the fancy descriptions and 
names, is a random wire antenna laid out through a hole in the the 
wall and along the ground. It is not a planned system with controlled 
directional response or characteristics, but rather just a wire that 
behaves like any other wire would if routed the same way and 
connected to the receiver.

Most Topband operators and many low-band DX'ers know that sometimes 
you can get lucky, and a totally "wrong" antenna will work after a 
fashion for receiving. It might be a 80 or 40 meter dipole, a ten 
meter yagi, or the aluminum clothesline in the back yard. The snake, 
being a random system with no special directional or noise response 
attributes, is no exception to this. That's why I suggested trying 
every possible antenna for receiving, if they can not install a 
planned system that will work by design.73, Tom W8JI 

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