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Subject: [AMPS] IMD
From: (Jon Ogden)
Date: Tue, 18 Sep 2001 07:13:18 -0500
on 9/18/01 6:38 AM, Peter Chadwick at wrote:

>> Reducing drive power from an exciter does not always make things
>> better. Quite often it actually makes things worse.
> Any exciter where that is the case requires adjustment - preferably with a 14
> pound sledgehammer, followed by a can of petrol and a lighted match.

I'd agree with Peter.  I can see a couple cases where it could get worse,
but I'd like to see Tom elaborate more.

A 1 dB drop in output power should result in a 2 dB drop in IMD
(theoretically of course).

Now, I guess there is the case of class AB amps that have the "banana"
shaped curve mentioned by someone else earlier.  That sort of sweet spot for
IMD is typical, so dropping power may cause IMD to get worse for a bit but
then it should eventually get better as stages are taken out of compression.
But I guess you can't really be too simplistic.  It all depends on how
stages are biased, where they are biased at, and the specs of each
individual stage.  So perhaps it's not just as simple as my theoretical
statement above.  It's a good maxim, but should be used, like any other
maxim, in the proper context.



Jon Ogden
NA9D (ex: KE9NA)


"A life lived in fear is a life half lived."

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