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

[Jim Brannigan]

    When Rich Measures article came out in QST, I send away for his
parasitic suppressers for my SB-220.
They cured all the problems in my amp.
I am not an engineer, but have been a ham since1963.
> 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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