[AMPS] impedance of nichrome lower

[Rich Measures]

>>Rich Measures wrote:
>>>During the grate suppressor debate, I repeatedly asked Mr. Rauch to design 
>>>a copper-wire parasitic suppressor that equaled the performance of the 
>>>resistance-wire suppressor. ... ...
...snip...
>A suppressor that clearly outperforms the Handy-Measures R-wire 
>suppressor tested by Wes, looks like it could easily be designed using a 
>copper-wire Ls.  For instance 200nH of Ls and 200 ohms of Rs would do it. 
>...  However, there seems to be a sticky wicket.  The C-reactance of a 
>3-500Z anode at. 29MHz is minus.1100 ohms.  With an anode RF potential of 
>up to 2700V rms, we have 2700v/100-ohms = 2.4A rms of RF current through 
>the suppressor.  
>The power being dissipated in Rs at 29MHz is: _____________?
>>
And the little red hen said........

I calculated the dissipation myself in the 200 ohm Rs and it was 42W at 
29MHz.   However, 42W will quite quickly evaporate any of the Rs 
resistors used either by Mr. Rauch (Ameritron-MFJ) or those used by us in 
our suppressor retrofit kits.  
-  With Rs kaput, the one and only current path is through the sliver, or 
copper, Ls  -- so, the result is virtually No vhf parasitic-oscillation 
suppression. .    . 

At 100MHz, the Rp of the 200-ohm Rs / 200nH-Ls  suppressor is 56.5 ohms 
-- clearly beating the pants off of the R-wire suppressor's 102 ohms and 
the W8JI suppressor's 166 ohms. 

Could such a suppressor be built using a 200-ohm, 50W Globar 
'non-inductive' resistor?  In my opinion, the Globar resistor would have 
too much intrinsic L to work properly in a VHF suppressor application -- 
because it would have about the same L as a typical Ls.  My best guess is 
that Rs should probably not have more than 1/3 the inductance of Ls. ... 
...  In our suppressors, the ratio is 1/5 or better -- using resistors 
that typically measure under 0.011uH each. (N7WS). .  

EDITORIAL: 
-  It seems that intrinsic L in Rs is Not Good.   It seems that intrinsic 
ESR in Ls is Good -- as Mr. Rauch apparently discovered shortly after his 
post of 11/28/96 -- wherein he proposed adding 5 ohms of ESR to Ls and 
calculating the results. .... Awesome idea, Tom,  AND your estimate of 5 
ohms was astoundingly close to Wes' subsequent measurement of 4.7 ohms at 
200MHz for the R-wire Ls.   CONGRATS.

Rich---
   

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


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