[AMPS] Parasitic suppressors/another question,

[John Fielding]

----------
> From: Jon Ogden <jono@enteract.com>
> To: John Fielding <johnf@futurenet.co.za>; amps@contesting.com
> Subject: Re: [AMPS] Parasitic suppressors/another question,
> Date: 07 April 1999 09:41
> 
> >As far as point #1 goes.
> >
> >Keying up an amp without a load connected and then finding that it 
> >oscillates is not a
> >sure way of telling if the amp is potentionally unstable.
> 
> And why not?  If the amp oscillates with no load, then it IS potentially 
> unstable.  Is it unstable in a place where you don't need it to be 
> stable?  Possibly.  But if it does NOT oscillate with no load, then it 
> rarely will oscillate terminated into a 50 Ohm load either.
> 
> This is somewhat of the principle behind a load pull test.  You either 
> short out or open circuit the output of an amp and then rotate it around 
> the Smith chart (via Ctune).  Also, the tank inductor generally provides 
> a large enough reactive impedance to VHF energy that it likely doesn't 
> matter wether you have a load on or not.
> 
> Having designed commercial 800 MHz amps in the past, I prefer to have 
> them stable (as much as possible) across all possible load conditions.
> 
> > Few high high gain 
> >amplifier devices are
> >unconditionally stable, and removing the output or input terminating 
> >impedance is almost
> >certain to provoke oscillation.  
> 
> Few properly designed amps.  I disagree with your statement.
> 
> >
> >Point #2
> >
> >How does this prove the amplifier is potentionally unstable?
> 
> If the amplifier starts oscillating after being "rung" by high speed 
> keying it IS unstable.  QED!  It's called transient response.
> >
> >Point #3
> >
> >How can you tell the difference between VHF energy which is caused by 
> >oscillation and VHF
> >energy caused by harmonic power by using the colour of a neon tube?
> 
> Because if the tube is keyed but has NO input signal, it should have NO 
> output signal.  If it does, it AIN'T harmonic energy but HF or VHF 
> oscillation.

Then how can the neon glow orange as you stated if no drive is applied?  Surely this must
be a test with drive applied.  And if it is with no drive applied and the neon glows
orange it means it is oscillating on or near the band selected - not so?

John	ZS5JF
> 
> 73,
> 
> Jon
> KE9NA
> 
> --------------------------------------------------------------------------
> Jon Ogden
> 
> jono@enteract.com
> www.qsl.net/ke9na
> 
> "A life lived in fear is a life half lived."

--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm