[Johnson] Neutralization vs. parasitic suppression, much moreinformaton is needed.

[Bill Evans]

Whatever Richard Measures "fix" does technically, it works.  I had a badly
parasitic commercial amplifier using two 3-500Zs that burned up its
bandswitch and was unquenchable.  Richard sent me one of his kits "gratis"
and asked me to give it a try.  No problems thereafter.

I'm sure some of the manufacturers debunk his work, but thankfully he is
still around.

Bill Evans
VE4UD

----- Original Message ----- 
From: "Gary Schafer" <garyschafer at comcast.net>
To: "Richard Peterson" <zapp11 at hotmail.com>
Cc: <johnson at mailman.qth.net>; <Sherrill.Watkins at dgs.virginia.gov>
Sent: Monday, October 04, 2004 3:36 PM
Subject: Re: [Johnson] Neutralization vs. parasitic suppression, much
moreinformaton is needed.


> Mr. Measure's parasitic chokes make sense if you think about what part
> is really the suppresser. The suppresser is the resistor part of it not
> the coil. The coil is there only to let enough of the high frequency
> parasitic develop across the parallel resistor so it can be absorbed.
> The coil shorts out frequencies that are lower (wanted frequencies). The
> idea of the nichrome wire is to lower the Q of the coil to broaden it
> out and also to absorb part of the parasitic.
>
> Parasitic are a result of resonance, at the parasitic frequency, in the
>   length of the plate lead of the tube and the length of the leads in
> the tank circuit combined. The same is true for the grid circuit
> combination.
>
> Often in audio amplifiers (such as the DX100 modulators) only resistors
> are placed in the plate and grid leads of the tubes at the tube
> connection to kill any parasites.
>
> 73
> Gary  K4FMX
>
>
> Richard Peterson wrote:
> > Sherrill:
> >
> > I am sorry I have not gotten back to you sooner. Been busy – and there
> > was LOTS of football to watch this weekend. That is always Job One for
me.
> >
> > Measure’s use of Nichrome wire as part of the way to cure VHF parasitics
> > in an HF amp is nonsense. First time I read it, I thought it had to be a
> > joke. But the truth is he sold kits and I suspect people installed them.
> > Too bad. It’s not science.
> >
> > You have to find the frequency of the parasitic (typically by use of a
> > wavemeter) and then you have to design and tune a trap to kill it. The
> > process and the cures are covered in the ARRL Handbooks, but not in a
> > great amount of detail. It seems (to me) that the older handbooks do a
> > better job. You will find the parasitic is often around 120 megacycles,
> > seems like. But a friend of mine reports he ran into a killer parasitic
> > around 50 megacycles in a piece of commercial gear made for the
> > government. And be advised, there are ham rigs out there with the
> > standard parasitic traps such as you described that still have
> > parasitics. Just because you install a resistor and add some turns of
> > wire around it doesn’t mean you have solved any problem! But the truth
> > is, many hams operate rigs with parasitics and they sound and work fine.
> > The problem does not always cause grief – just as you can operate a
> > final that is not neutralized, and often it is satisfactory.
> >
> > However, it can be hard to tune a rig that has BAD parasitics – it can
> > act really “goofy” and meters read all over the place – and that’s
> > because the amplifier has more than one frequency in it.
> >
> > You will find some testing procedures described in the Handbook.
> >
> > I’m glad you are interested in this. It’s good to find hams who want to
> > know, rather than you merely want to tune, talk and ship if it breaks.
> > The latter seem to lose interest in the hobby after awhile. Not always,
> > mind you, but often. The guys who tinker seem to get more out ham radio.
> > Just don't let the (seeming) complexity of it bother you -- 27 years ago
> > when I got my license, I drove myself crazy trying to understand how to
> > hook up something as simple as a VR tube.
> >
> > And I still don't know much today -- but enough to get by.
> >
> > Richard, WB5NEN
> >
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