Towertalk
[Top] [All Lists]

Re: [TowerTalk] use of RG11 coax - 75 ohm

To: "towertalk@contesting.com" <towertalk@contesting.com>
Subject: Re: [TowerTalk] use of RG11 coax - 75 ohm
From: "Jim Brown" <jim@audiosystemsgroup.com>
Reply-to: Jim Brown <jim@audiosystemsgroup.com>
Date: Tue, 29 Mar 2005 22:24:34 -0600
List-post: <mailto:towertalk@contesting.com>
On Sun, 27 Mar 2005 10:01:23 -0500, Tom Rauch wrote:

>but for longer feedlines 75 is a good option.

Yes. I'm still a fan of 75 ohm cable for dipoles that are relatively 
high (as a fraction of a wavelength) and otherwise in the clear, and 
50 ohm cable for those that are relatively low. The reason -- if you 
study models in the various texts (ON4UN, and others) for the 
impedance of dipoles, they tend to vary around 50 ohms +/- 33% for 
low dipoles, and around 70 ohms +/- 33% for higher ones. In other 
words, the presence of ground affects the feedpoint impedance, but 
tends to approach 70 ohms as the antenna gets further from ground. 

Jim Brown  K9YC


_______________________________________________

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>