[AMPS] Self oscillation with homebrew 3-1000Z ????

[Steve Thompson]

-----Original Message-----
From: measures <2@vc.net>
To: AMPS <amps@contesting.com>
Date: 07 May 2001 14:57
Subject: Re: [AMPS] Self oscillation with homebrew 3-1000Z ????


>
>>
>>Jim,
>>
>>I reckon there are two important steps in sorting a problem of this sort.
>>
>If the osc. is continuous, you cold find the freq. with a
>dipmeter/wavemeter.

Agreed - we all get used to our own toolkit. A wavemeter might not find a
vhf oscillation at the output socket of a hf amp, so you might need to have
the lid off and ht on. Lid on and ht on is safer.
>
>>1. Get some sort of spectrum analyser, or even a scanner, and find out
what
>>frequency the oscillation goes off at.
>>
>>2. Try to put a scalar analyser through the amp, firstly when its cold,
and
>>look for frequencies where there's a peak in response. You will probably
>>find one around the frequency you measure in 1. You can then look for
>>changes in circuit or layout that kill the peak. Once the peak is gone,
you
>>can repeat the test with the amp active.
>>
>>Ok, not everyone has a swept system, but you can do it with a very basic
>>spectrum analyser and signal generator. You might have to spend a little
>>time and beer money finding one to borrow, but it's a quicker and better
>>route in the end.
>>
>I would bypass the high-tech research, cut to the chase, and try a lower
>Rp suppressor.

That will often work, but it might be curing the symptoms rather than the
problem.

Steve



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