On Tue, 20 May 1997 14:50:13 +0100 "Ian White, G3SEK"
>> According to Wes' (N7WS) tests on otherwise-similar suppressors, a
>>copper coil Ls produced about 2/3 more Rp at 100MHz than a Ni-Cr-Fe
>>Ls. Since VHF voltage amplification is a pretty much Mu x VHF-Rp,
Ian; my message to Tom predates this reply but bear with me please. I
have a strong belief that Rich's only mistake is in the terminology and
the way he presents it. Tom realizes this and has capitalized upon it
>NO! This is where Rich still doesn't see it. He misses out the
>parallel -> series circuit transformation - and that turns all his
>Gary Coffman posted the analysis in r.r.a.homebrew several months ago.
>I'll try for one last time.
Who is Gary Coffman?? If his information was so good, please repost it
here for us that dont spend our lives on the Internet.
>Here is the VHF resonant circuit, pretty much as shown in all the
>textbooks and Rich's own web page.
> ---X_Lp-- X_L_stray
> -------- |------))))))--------
> | |__Rp___| |
> ___ |
> ___ Anode etc capacitance Ca Pi-tank C1
> | |
> | |
>The suppressor is represented by the equivalent parallel resistance Rp
>and parallel inductive reactance X_Lp as actually measured at VHF
>a network analyser. (This puts all types of parasitic suppressor on
That circuit came across very poorly on my Juno E-mail program; cant even
hope to make it out. I prefer Juno for E-Mail as do others here Ian. I
can also access any WWW URL simultaneously which allows me to "surf" and
type E-mail under a split screen. Yes, other programs allow this also
but not with the ease and clarity of a Juno screen.
>Note that some components are connected in series, while others are in
>To determine the Q of this tuned circuit, we need to transform all the
>series/parallel components into an equivalent combined form that is
>either TOTALLY series or TOTALLY parallel. Let's go for the
> | | |
> ___ | )
> ___ Ce Re ) X_Le
> | | )
> | | |
>At the VHF resonance, Q is going to be given by either
>(Re / X_Ce) or (Re / X_Le). Higher Re means higher Q and higher
>If you want the detailed math, DejaNews your way back to Gary
>posting, or find it in the web archive of that marathon debate.
>What comes out is that if Rp in the suppressor is high, Re in the
>equivalent parallel network is LOW. There is an impedance *INVERSION*!
Of course there is an Inversion if you and others continually insist on
mixing Parallel and Series circuits. Why not just ask Rich to clarify
his statements instead of pontificating? We can not all be experts in
Engineering, Linguistics and Semantics at the same time....some of us
work for a living.
>That means that higher Rp in the suppressor leads to a LOWER loaded
>Q and LOWER VHF-gain -
I agree 101% Ian and was what I tried to say earlier today.
exactly the opposite to what Rich still persists in saying.
BUT I just dont believe that is what Rich is TRYING to say......sorry
Rich if Im trying to put words in your mouth.
Lots of Snips....
>In the VHF region:
>"As the chart shows, there are only slight
>differences between the effective parameter values for the
>two types of networks."
>In the HF region:
>"It can be noted that the conventional suppressor will have a greater
>percentage of the total current flowing in the inductive (lower
>loss) leg in the HF region than will the nichrome type."
A very ambiguous statement since it assigns no values to "percentage".
How can one compare a conventional L made of #12 wire with Rich's #20 (?)
Nichrome. Even comparing apples to apples there would be a difference.
Instead, Wes's statement would offer some validity if it showed the
percentages of desired vs undesired energy before and after the
suppressor. Obviously this would require a bit of sophisticated test
equipment and knowledge how to properly use it and interpet the
>I concur totally with Wes. His measurements show that the significant
>differences are at *HF*, not at VHF.
I feel that you are both very wrong Ian. My own limited tests show that
the material used plays a very small part at HF and the effect increases
My limited testing is based upon the theory " If it smokes it aint
correct ". Testing was performed on many amps using from one to four
each 572B's and 3-500Z's. Frequencies of interest were 28 and 50 MHz for
Anyone interested in expanding their knowledge instead of playing an ego
trip bashing game please contact me. I will be glad to send full mfg
specs on the VHF resistive material I have been using for about 35 years.
>Finally, let me say that I don't know whether Rich's parasitic
>suppressors have any benefits over conventional ones or not.
Neither do I in some situations BUT at least I have gone out and bought
them and evaluated them....what have you done???
I find them helpful at times and yet I can easily smoke them at
50MHz....but they have not been claimed to be effective there either.
>I don't have any professional stake in this debate. My only interest
>to find a technically valid explanation of the confusing mess of
As an author you have a VERY PROFESSIONAL stake in this Ian; information
to the contrary could affect your book sales.
My own interest is both professional and financial since I work on amps
for a living. Any improvement to both my knowledge and bank account is
most unashamedly welcome.
>73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
> 'In Practice' columnist for RadCom (RSGB)
>FAQ on WWW: http://www.contesting.com/ampfaq.html
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