Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!sun-barr!ames!pasteur!ucbvax!hplabs!hp-pcd!hpcvaac!billn
From: billn@hpcvaac.cv.hp.com (bill nelson)
Newsgroups: sci.electronics
Subject: Re: Re:TV Antennas, the knob
Message-ID: <6690003@hpcvaac.cv.hp.com>
Date: 31 Dec 90 20:03:29 GMT
References: <14239@mcdphx.phx.mcd.mot.com>
Organization: Hewlett-Packard Company, Corvallis, Oregon, USA
Lines: 17

depolo@eniac.seas.upenn.edu (Jeff DePolo) /  9:04 pm  Dec 16, 1990 / writes:

>>	b) Terminated it poorly or are using the wrong impedance cable
>>	    (you'd better be using 75 ohm coax (not 50 ohm!) or 300 ohm twin
>>	    lead).

>You'll realize little difference between 75 ohm and 50 ohm coax.  When
>you consider what a wide range of frequencies you are attempting to
>receive, even with a well designed log periodic, the feedpoint 
>impedence is going to vary over quite a wide range.  Choose the cable

Absolutely correct - I believe the primary cause of the impedence variation
is due to mounting height variation.  I know the effect decreases as the
height (in wavelengths) increases.  I don't think the 25-40 ft above ground
level is enough to minimize this factor.

Bill