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Re: [TowerTalk] antenna FS measurements

To: <>
Subject: Re: [TowerTalk] antenna FS measurements
From: "Tom Rauch" <>
Reply-to: Tom Rauch <>
Date: Wed, 30 Jun 2004 07:25:26 -0400
List-post: <>
> I don't know about that... The linearity can't be all that
bad, or you'd
> have terrible IMD kinds of problems.

Receivers are for the most part acceptable in mixing and
distortion to our ears (not to  a precision instrument)
because they have AGC, and because they limit the number of
signals that can mix by using narrow filters. I can't
imagine shutting off the AGC in my radio and simply
adjusting the volume control to set level.
That why radios using DSP systems as primary selectivity are
so poor within roofing filter bandwidth (look at the 756PRO
or TS2000) and it's why PSK people whine when anyone comes
near them with more than 20 watts into a wet noodle.

Besides, you are forgetting an amplifier can have
non-linearity without serious IM distortion. Case in point,
triodes and FET's. Even a class C RF amplifier can sound
pretty clean to the ear on frequency. It all depends on the
slope of the gain error.

The idea we can turn off AGC and measure everything on the
audio line just isn't a good idea unless we restrict the
level variation at the receiver input.

73 Tom


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