Towertalk
[Top] [All Lists]

Re: [TowerTalk] fiberglass guys

To: Cqtestk4xs@aol.com, TOWERTALK@contesting.com
Subject: Re: [TowerTalk] fiberglass guys
From: Jim Lux <jimlux@earthlink.net>
Date: Wed, 21 Sep 2005 20:11:41 -0700
List-post: <mailto:towertalk@contesting.com>
>
>I can tell you experience trumps theory on these things. I have had several
>antennas (tribanders and monobanders) mounted down the tower where they were
>pretty close to the EHS guy wires.  SWR was always changed for the better 
>when
>the EHS was replaced with Philly or Polyrod, sometimes significantly.

SWR doesn't tell you anything about pattern. It just happens to be easy to 
measure, and unexplained changes in SWR tell you that something in the 
antenna system has changed, so it's a very useful diagnostic tool.

A 3 dB pad in series with the feedline will dramatically improve the SWR 
and the apparent bandwidth will also increase, but is probably not a 
desirable strategy in general.

In your specific case, the change in SWR (presumably from the 
manufacturer's data, or from free space adjustment) tells you that there's 
some sort of interaction, and, in general, interactions are bad, but not 
always.

Compare a dipole and a 5 element yagi with closely spaced elements. The 
dipole will have an impedance of about 70 ohms, and so will present a much 
better than the Yagi, which will might have a feed point impedance of 10-15 
ohms (without the matching network).  The Yagi's also narrower band, once 
you've matched it, particularly if you use a reactive matching network (as 
opposed to, say, a tapered transmission line or a broadband transformer).




_______________________________________________

See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather 
Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions 
and ask for Sherman, W2FLA.

_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk

<Prev in Thread] Current Thread [Next in Thread>