Topband: 75ohm coaxial snake beverage?

[Roy Morgan]

At 08:49 PM 7/24/2006, Felipe Ceglia wrote:
>... RGc-6 and RGc-11 75 ohm catv coaxial cable... if it is possible to 
>make snake beverages with these cable instead of 50 ohm.

Felipe,

(I have not yet put up any kind of Beverage - I just moved to a place that 
has the room three weeks ago.)

I was reading ON4UN's book yesterday, including the section on snake 
antennas, or "BOGs", Beverages On the Ground. I remember these points:

1) They should work well, and are recommended if you can't put up the 
supports for a Beverage in the air.

2) They can be expected to deliver signal strengths 8 to 10 db less than 
the normal Beverage.  Thus a preamplifier may be needed.

3) Because of the lower signal levels, de-coupling the feed line is 
very  important: Common mode signals (the feed line outside conductor 
acting as another antenna) are even more troublesome than with normal 
Beverages.  Do not ground the shield at the antenna feed point, use choke 
beads on the feed line, in at least one location, possibly more, and ground 
the feed line outer conductor at least 5 meters from the antenna feed point.

4) If you use coax as you indicate, a bi-directional antenna is possible, 
with the signal from the far end of the antenna returning through the 
inside of the coax.

5) Lew McCoy published information about antennas on the ground.  ON4UN 
states that  none of the configurations described by McCoy in the 
referenced publication will work as a Beverage.

6) Use of 50 or 75 ohm coax, at least in the feedline, makes no difference 
whatsoever. Using coax that is well shielded DOES make a difference. Some 
coax has very poor shielding and should be avoided for sure.

7) (?) The velocity factor may be influenced by the ground, so if you are 
attempting to find a "sweet spot" in the length, take this into account.

I suggest you put your antenna out and let us know how it works.

Roy

- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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