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[TowerTalk] antenna FS measurements

To: "Towertalk" <>
Subject: [TowerTalk] antenna FS measurements
From: "Jim Jarvis" <>
Date: Tue, 29 Jun 2004 15:19:56 -0000
List-post: <>

W/resp to antenna pattern measurement techniques, some very important things
been posted here, in fragmented form, from several knowledgeable guys:

*  You can measure at 0 degrees azimuth, using a friend a few miles away, on
*  Use the telephone (or 2 meters) as a backchannel for coordination &
*  Vary the TX power, holding S meter reading constant.  Use a real
        Take data at fixed rotational intervals.
*  If possible, disable the AGC and digitize the audio in your soundcard,
instead of
        varying TX power. (The latter, of course, seems to lack a software
*  Recognize that the pattern at 0 Az. isn't the same as at real arrival
        The data will be useful for comparing antennas against each other, or
against models,
        but NOT as an absolute.  It will be affected by terrain and structures. 
        be adequate to determine 'reasonably correct' function, decoupling of
feedlines or
        adjacent antennas, etc.  I have found that it validated specifications 
on a
        T8, 3 el SteppIR, and multiple kt34A and XA's.  And, of course, 
the 6dB f/b
        ratio on my vertical, which was coupled to the lpda via common-mode 
on the feedline.

As an aside, there's a program called "S-Meter", which takes meter readings
via the radio
interface, for those rigs which report S meter data.  While this leaves you
open to
measurement error due to the AGC response curve, it should produce a
visualization of the
pattern.  My sense is, most S meters tighten up above S9, and may expand
below S3 or so,
and it will tend to understate gain and f/b, and overstate the depth of

The LPL technique, of holding S meter constant and varying TX power, will
eliminate that.
So would turning off the AGC and digitizing the audio.

If anyone finds a program to support the latter, I'd like to know about it.



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