>Actually there seems to some "confusion" about the change caused by
>nichrome. I don't intend to argue this, so this will be my single
>group post on this subject. People should use common sense and
>think about this stuff *very* carefully.
>
>Wes Stewart's conclusion was there is no real difference at all in
>VHF performance no matter what type of material is used in the
>inductor, ....
As I recall, this appears to be pretty much what Wes believed before he
made the VHF suppressor measurements. Wes presumed--perhaps because the
"recognized expert" said so--that any result could be obtained by simply
juggling Ls and Rs. And it's absolutely, positively, 100% true.
....... However there is one unteensy, unweensy problem:
IF Ls is increased to obtain increased VHF-performance (lower Rp) , the
28MHz voltage drop across Rs increases. At some point, Rs burns out.
With Rs up in smoke, the overall Rp for the anode's VHF resonant circuit
increases substantively, as does VHF voltage amplification. Next stop:
Regenerationville?
The advantage of using resistance-wire for Ls is that it provides the
VHF suppressor designer with a substantive reduction in VHF-Rp WITHOUT
any increase in Ls. This is essentially what the legendary Mr. F. E.
Handy was telling us in the 1926 Edition of *The Radio Amateur's
Handbook*. when he wrote:
"The combination of both resistance and inductance is very effective in
limiting parasitic oscillations to a negligible value of current."
[note: "F. E. Handy" was apparently NOT in Mr. Rauch's dictionary
during the vhf parasitics debate.]
>.....that even a very small change in resistance or turns could
>easily produce identical results at VHF. There was no "magic", the
>suppressors were essentially the same, or could easily be made to
>appear the same.
How true, how true, Mr. Rauch. However, during the vhf suppressor
debate, I repeatedly asked the naysayers in the Rauchian camp to design a
suppressor (with a 0-ohm ESR Ls) that would replace the c. 5-ohm ESR
Ni-Cr-Fe AG6K suppressor that Wes measured. Ian White announced that he
could do so. He did not. You said you could do it. You did not.
For anyone who wants to have a go at it: In the March, 1989 issue of
*QST* magazine, there is an article titled "Calculating Power Dissipation
in Parasitic Suppressor Resistors" that might be worth perusing. The
shortcut calculation method is within 10% of the legit calculation using
integral calculus The article also covers series/parallel equivalent
circuit conversion.
Anybody who understands series/parallel circuit conversion should be
able to design an excellent, very low Rp, VHF parasitic suppressor using
silver plated strap that will easily outperfom the AG6K suppressor used
in Wes' measurements. The great hurdle is to design one that will not
burn out Rs at 28MHz.
...snip...
>...why is lower Rp suddenly a better method of reducing VHF gain,
>contrary to what we all experience in actual circuits???
...snip...
Suddenly? This information has been in the VHF suppressor retrofit kits
for a long time.
In 1990, I wrote:
"The second job of a suppressor is to reduce the VHF voltage-gain of
the amplifier-tube.
--- The voltage-gain of an amplifier-tube is approximately proportional
to the output load-resistance (RL) placed on the anode of the
amplifier-tube. Higher-RL means higher voltage-gain and lower RL means
lower voltage-gain. If the VHF voltage-gain of an amplifier-tube can be
made low enough, by decreasing the VHF RL, the VHF voltage-gain of the
amplifier-tube will be so low that it can not sustain oscillation."
Sure, Rich, RL was not a satisfactory term to use because it is also
used to designate the anode load R in tank calculations in *Care and
Feeding.....*. . VHF-Rp is a better name because it denotes that a
parallel-equivalent of the anode's (series) VHF suppressor is involved.
During the vhf parasitics debate, as posted on November 28, 1996, Mr.
Rauch proposed that WE run through some sample calculations for a
suppressor made from nichrome-wire versus one made from copper-wire. He
proposed that an ESR of 5 ohms be assumed for the nichrome suppressor
calculations. However, before I had time to do the calculations, he
suddenly cancelled his 11/28/96 post. Mr. Rauch subsequently
stonewalled any and all references to the post he cancelled
Mr. Rauch's mysterious 11/28/96 post can be found in Will's archives at:
http://www.av.qnet.com/~kn6dv/
Rich---
R. L. Measures, 805-386-3734, AG6K
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