>Rich wrote
>> I have never claimed that our suppressors stop parasitics. . In
>> Wes' suppressor tests, Rich's suppressor exhibited around a 40% improvement
>> (decrease) in parallel equivalent resistance (Rp) at 100MHz compared to a
>> conventional suppressor. I have claimed that a decrease in VHF-Rp
>> results in a decrease in VHF gain at the anode-resonance.
>> >...........
>>
>Interesting you bring this up. You used Wes' tests many times in your
>mails to the reflector, and even used to have a link on your web pages
>to his web site. Interesting enough, that link has now gone,
When Wes' Website was removed from the Web, I removed the link.
>and now you only show one graph supporting your claims.
VHF-Rp is the issue in VHF parasitic suppressor design since Rp and tube
Mu are determiners of VHF voltage amplification. Since Mu is semi-fixed,
one needs to come up with minimal VHF-Rp in order to obtain minimal
VHF-gain. The Rp graph is the only graph I have used, however, a graph
of VHF-Q would look similar. For instance, at 150MHz, the copper-wire
suppressor had a Q of 1.3 while the semi-similar resistance-wire
suppressor had a Q of 0.9., so either by comparing VHF-Rp or VHF-Q, a
similar copper-wire suppressor has more than 40% more of what the
designer does not want compared to a resistance-wire suppressor. .
> Good that there are still search engines on the web. For those interested,
the full (or
>should I say real) story is at:
>
>http://www.azstarnet.com/~n7ws/supp-2a.htm
>
>A quote from that page:
>
>"Some mathematical manipulation can demonstrate that shunting the
>conventional suppressor with additional resistance will bring the curves
>into better alignment. An additional 250 ohm resistor in parallel with
>the network will cause the Rp curves to nearly overlap the nichrome
>curves above about 30 MHz.
When one calculates the admittance and parallel-equivalent resistance
(Rp) of the VHF suppressor's Ls/Rs parallel circuit, one finds that as Rs
and Ls Increase, the resultant Rp Decreases. Thusly, Rp could be
decreased if the existing 100 ohm Rs were replaced by 250 ohms. However,
if the 100 ohm resistor were paralleled by a 250 ohm resistor, as Mr.
Stewart suggests, the resultant 71 ohms of Rs Increases Rp, which would
move the Rp curves farther apart.
>Below 30 MHz, the Rp of the adjusted
>conventional type will be higher than the Rp of the nichrome device.
The Rp of the copper-wire suppressor is already higher at <30MHz,
however, what is more important in a VHF suppressor, 1/2 % more power to
the antenna at 28MHz, or a 40% reduction in VHF voltage amplification at
150MHz?
>a parasitic suppressor functions as described by conventional wisdom,
>then this should be a more desirable case."
>
Conventional wisdom tells this ol' fart that it might not be a bad idea
to perform the required calculations using susceptance, conductance,
admittance, and parallel-equivalent conversion to see what is going on
Before opening my large mouth.
>Another quote from N7WS' web site:
>
>"This graph compares the loaded Q of a W8JI (conventional) and AG6K
>(nichrome) suppressor. Note that the HF Q for the conventional
>suppressor is higher than the nichrome type. At VHF, the two types are
>essentially equivalent.
>
Is a (VHF) Q of 0.9 "essentially equivalent" to a Q of 1.3?
>In other words, unless you're selling nichrome wire, there ain't a
>dime's worth of difference. If you are selling nichrome wire, then
>there's about $20 worth the difference, in your favor."
>
1.3/0.9 = 1.44 Is a difference of 44% worth anything?
>This latter statement can be found on:
>
>http://www.azstarnet.com/~n7ws/supp-3a.htm
>
>Conclusion #1:
>
>The effectiveness of a suppressor has nothing to do with whether you use
>Nichrome or not, but is only depending on using the right combination of
>R and L.
>
This is mostly true, however, there is one catch, Mr. Geurts. When one
decreases VHF-Rp by increasing Rs and/or Ls, the 28MHz-dissipation in Rs
increases exponentially. In the example I presented here a few months
ago, I increased Rs in the W8JI suppressor from 100 ohms to 200 ohms, and
I increased the inductance of Ls from 100nH to 200nH. The result was an
improvement in suppressor performance, due to Rp being markedly lower
than the resistance-wire suppressor. . . However, the catch is that
the dissipation in Rs was 40-odd watts. Try finding a 200 ohm resistor
that has an intrinsic L of less than 15nH, which can dissipate 45W. .
The bottom-line is that using a resistance-wire Ls instead of a
copper-wire Ls serves to decrease the dissipative burden on Rs at 28MHz.
In other words, adding a few ohms of ESR to Ls at VHF, by the use of
Ni-Cr-Fe conductor material, has a pronounced effect on the dissipative
requirement in Rs. . .
. On November 28, 1996, during the grate vhf suppressor debate, Mr.
Rauch proposed that we perform the necessary calculations to analyzize
just such a suppressor inductor and compare results. However, he quickly
and quietly cancelled this post, and he would not discuss his proposal or
the reason why he cancelled it.
>Conclusion #2;
>
>This doesn't mean that Rich's suppressors don't work, because they might
>well be the right (or even the optimum) combination of R and L.
>
In the measurements Wes performed at 100MHz, the copper-wire (W8JI) VHF
suppressor had a 9% advantage in Rs and a 34% advantage in Ls -- and yet
the Ni-Cr-Fe resistance-wire suppressor exhibited a 40% advantage.
>Conclusion #3:
>
>If you quote someone's work, make sure you quote all of it, not just the bits
that suit you.
>
According to U. S. Copyright Law, a "fair-use" quote must contain only a
portion of the copyrighted material. Wes made a lot of measurements. I
quoted only the measurement that affects VHF voltage amplification of
the amplifier tube -- i.e., VHF-Rp.
Editorial Comment:
- During the grate parasitics debate, I repeatedly recommended that
Messrs. Rauch and Stewart refer to the March 1989 issue of *QST* and
calculate the 28MHz-dissipation in Rs.
I did this because I knew that when Ls and Rs are increased to improve
Rp, dissipation increases exponentially. However, for some mysterious
reason, they apparently never bothered. . . If they had done the
calculations, they would have also discovered that, although both of them
were correct in saying that a copper-wire VHF suppressor could be
designed that would outperform a resistance-wire VHF suppressor, the
trade-off was summary destruction of any commerially available resistor
that has a low-enough intrinsic-L to used for Rs.
If anyone has a theory on why Messrs. Rauch and Stewart seemingly did not
perform these calculations, I would like to hear it.
- thanks
cheers
Rich...
R. L. Measures, 805-386-3734, AG6K
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