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[AMPS] Suppressors, measurements, and acrimonious blather

To: <amps@contesting.com>
Subject: [AMPS] Suppressors, measurements, and acrimonious blather
From: 2@vc.net (measures)
Date: Thu, 3 Aug 2000 15:11:30 -0700
>
>Paul wrote:
>>
>> > The only useful
>> > goal with today's technology is to not allow the parasitic oscillation 
>>to
>> > start in the first place.
>>
>>Help me here.  Isn't this the purpose of the suppressor?  That is , it's
>>function in design is not only to limit parasitic currents to a "negligible
>>level," but more importantly "suppress" the oscillation from occuring "in
>>the first place?"
>
>Your point is precisely mine.  The function of a parasitic suppressor in 
>today's environment is no longer mere suppression, but outright prevention  
>This was not the case in the 1920's.  Many articles were written concerning 
>the design of filters that would filter out the spurious oscillations that 
>everybody expected to exist.  This is why I am suspicious when a designer 
>uses 1920s theories to design one of today's devices.  The purpose is 
>different today than it was "back then".  

? "back then" VHF parasitic suppressors were never used to absorb the 
considerable energy of the actual oscillation.  Like today, they were 
used to reduce VHF amplification at the anode-resonance.  

>  Unless, of course, one is using a 
>valve from "back then".
>
>> > There is no need to pound repetitively
>> > on the nail of suppressor Q when a few hours work with a nearly free
>> > software package will show whether it makes sense to do so or not.
>>
>>Unless you believe that modeling is not perfect in all cases and measuring
>>resonances in the completed, constructed circuit is a better attempt.  
>>Seems
>>there's an analogy to be made between the accuracy of circuit modeling and
>>the accuracy of antenna modeling software when ground effects are
>>considered.
>
With proper modeling a three element Yagi can have 12db gain.  

>The person who is performing modelling correctly endeavours to model all of 
>the stray elements, in addition to the intended elements.  I have not seen a 
>case yet where a model could not be derived for a real-world application.  
>Proper modelling always is a back-and-forth activity between the model and 
>the manifestation.  In the end, you will have an accurate model, and a 
>physical implementation with extremely predictable behaviour.  

?    [chortle].  There is assuredly nothing predictable about parasites.  
Murphy was right.  Things are more complicated than they look.  

>Without the 
>model, you cannot produce such predictability, and without the physical 
>implementation, you cannot test the model.
>
>>I too am perplexed by the ongoing suppressor controversey and it's function
>>seems to be nearly as mystical as that accorded by the dreaded balun.  I
>>question the placement of some type of anode suppressor in nearly every
>>commercially-manufactured amateur amplifiers when most of the same
>>manufacturers would have you believe that 1) their amplifiers are 
>>ultimately
>>stable, and 2) suppressors are not required in "well-engineered" designs.
>>If conditions 1 & 2 are met, isn't it ridiculous to include the suppressors
>>in their designs?  Or, is the inclusion of the suppressor in their
>>amplifiers that little bit of insurance against "the unknown?"
>
>I cannot speak for the behaviour of other manufacturers.  I have used 
>suppressors myself, but only after measurements proved that they were 
>required.  There are some valves which, due to their physical size, are 
>difficult to tame.
>
>In commercial industry, the topic simply does not come up.  If your 
>measurements demonstrate that you need a suppressor, you use one.  Why it 
>occupies so much email bandwidth in this circle is really quite a puzzle to 
>me.
>
It is a puzzle to me as well.  Virtually every thing was known by 1935, 
yet the taurine feculence and hairpull continues.  .  
>
cheers, Fred

-  Rich..., 805.386.3734, www.vcnet.com/measures.  
end


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