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[AMPS] suppression

To: <amps@contesting.com>
Subject: [AMPS] suppression
From: measures@vc.net (Rich Measures)
Date: Thu, 22 May 97 12:35:35 -0700
>Hi Bill,
>
>> I think I see a basic error in the above.  The R introduced by the
>> nichrome-wire suppressor isn't Rp, it's Rs - so it's in series with
>> the suppressor inductance, not in parallel.  Right?
>> 
>> 73, Bill W7TI

Right.  
The nichrome wire's built-in series-R was but a few ohms at 100MHz.  
However, these few ohms decreased the parallel-equivalent R (Rp) of a 
3-500Z's VHF suppressor from 166 ohms to 101 ohms.  

>Hi Bill,
>
>No, that's not exactly correct. Let me take a stab at "un-confusing" 
>this issue.

So now there's an "exactly correct" in addition to plain old-fashioned 
correct.  I'm confused already.  
...snip...
>We all know adding turns to the suppressor makes most PA's more 
>stable at VHF. 
--true
>The bigger the coil, the better the stability but 
>the bigger the resistor also has to be. A bigger suppressor has 
>higher Rp.

'Bigger' has nothing to do with Rp.  There are four determiners in 
arriving at Rp.  
1.  The resistance of Rs.
2.  The series-inductance in Rs (9nH in the resistors used in our 
suppressor retrofit kits) 
3.  The inductance of Ls.
4.  The series-resistance in Ls.  (the difference between traditional 
suppressors and R-wire suppressors)

>The reason a higher Rp value in series with the anode DECREASES VHF 
>gain more than lower Rp value is simple to explain. ........

Bzzzzzzzzzzzzzzzzzt.  (cough, cough)  
Mr. Rauch is essentially saying that voltage amplification is  equal to 
Mu*(1/Rp).  However, the second term in the accepted formula is NOT a 
reciprocal---i.e., the accepted formula is:  Mu*Rp.   

...snip...
>Series resistive losses (such as winding the coil from a lossy 
>material) in the coil have greater effect as the frequency is 
>lowered, ...

Lowered?.........According to Wes' measurements, the nicrome-60 
(NI-Cr-Fe) coil exhibited 0.47 ohms of ESR at 10MHz and 4.7 ohms of ESR 
at 200MHz.  If what Mr. Rauch says is true, silver plating has a greater 
effect at low frequencies.  If what Mr. Rauch says is true, UHF cavities 
should be surfaced with nichrome foil.  
...snip...
>If we add a suppressor with too much Rp, it might get too hot on ten 
>or 15 meters.  

The W8JI suppressor exhibitited about 2/3 more Rp than the AG6K 
suppressor.  Does this mean that the W8JI suppressor might get too hot on 
10m or 15m?

>This stuff really isn't that complex, it's just no one has ever 
>written anything detailed in amateur publications. 

Hmmm.  That statement explains a Great deal.  Reid Brandon said there 
were no articles in QST on vhf suppression.  Amazing.  

>The lack of articles is probably why engineers (like Ian, N7WS Wes, 
>Gary Coffman, and so on), who learn this stuff formally and use it 
>every day, often get perplexed or irritated when someone 
>appears to "twist it all up".

Mr. Rauch:  In your opinion, would inverting a term in an established 
formula qualifiy as twisting?

 Neither Messrs. Coffman, Rauch, Stewart, or White has so far delivered 
on the Ls/Rs values for a conventional VHF suppressor that would produce 
a lower VHF-Rp than the resistance-wire VHF suppressor.  And why not?  
Are they perhaps perplexed by a certain uneasy feeling that they just 
might be walking into an ambush?  

Rich---


R. L. Measures, 805-386-3734, AG6K   


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