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

[Richard Peterson]

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

_________________________________________________________________
Don’t just search. Find. Check out the new MSN Search! 
http://search.msn.click-url.com/go/onm00200636ave/direct/01/