[Amps] Re: IM Distortion

[RFlabnotes at aol.com]

Ian:
       There are a few very technical points to consider here (that actually 
do affect the relavence of all of this) and I think it best we discuss it 
offline. If we come to any earth-shaking conclusions, we can issue forth a 
manifesto.

       I would like to clarify my point about the standards, etc. It didn't 
come through very clearly, as I now see. Here is all I meant.

       I was hypothesizing that we (you,me,everyone interested and involved 
in this issue) come to an agreement about a standardized measure of IM. You 
may recall that it was you who suggested the possibility of the adopting the 
'GM4RFX Method" and codifying it formally, so that it became the standard 
test (possibly even using a standardized voice tape sample). Then, as I 
pointed out, who is going to establish the actual numerical limit value(s) to 
be used when the test is run in the ham stations of the world? It is NOT a 
trivial issue, mainly because it puts the person(s) entrusted with setting 
that standard in the position of having to try to make a value judgement (how 
many Zorkons=intolerable splatter?). 

       As regards every ham making his own measurments and value judgements, 
in that perfect world everyone would do this dutifully like you, the bands 
would be totally clear of splatter, and Sadaam would be teaching Sunday 
school. But in this world that I know, people are going to be somewhat less 
than civilized. Specifically, many hams are going to buy their amplifiers, 
hook them up, and do everything they can to hold the plate current meter up 
as high as possible when they speak. The ONLY thing that will control them at 
all is whatever hardware limiting,filtering,sensing,etc. is built into that 
amp and is OUT of user control.

 The guy who designs that amp has to have standards to follow - there is no 
other way. Where do those standards come from? Well, they originate from 
places just like this. The people who are concerned and affected try to pool 
their their opinions and needs, which hopefully get weighted into the final 
numbers that appear in those standards. 

P.S. Voice-signals have a pseudo-random nature that is very likely to cause 
TIM from mechanisms that would not occur with steady-state tones. So TIM is 
an inherent part of this issue, like it or not.  The spectral-averaging 
method would certainly detect these, but the problem is, would it properly 
weight them?

73
Eric K8LV