>km1h @ juno.com wrote:
>
>>>
>>>With a wide enough choice of R and L values, it is ALWAYS possible to
>>>reproduce Rp, Lp and therefore Q, at ONE frequency.
According to a graph of Wes' measurements of the similar suppressors, the
Rp (and Q) values seem to parallel each other over a fairly wide range of
frequencies, separated by a gap of roughly 40%. .
>>>There is absolutely
>>>no doubt about that. Naturally you would choose the frequency of the VHF
>>>parasitic resonance in the PA that you're trying to suppress.
- The Ls/Rs values are not selected to target one frequency. Rs/Ls is a
broadband circuit. The primary consideration in designing a VHF
suppressor is Not in securing the lowest VHF-Q and VHF-Rp at the anode's
VHF resonance. Instead, it is reducing Rp without blowing Rs at 29MHz
during RTTY, FM, or A-zero transmissions. If Rp blows, Rp and Q go
through the roof- - and there is virtually No VHF parasitic suppression.
>>
>>Which is roughly determined to be the frequency of the highest amount of
>>G-P feedthru...is that a valid assumption Ian?
In my opinion, not always. It is undoubtedly true that a greater amount
of anode-to-grid feedback occurs at the second anode-resonance. However,
this resonance -- which is typically 300 to 500 MHz -- is only likely to
be a problem with UHF-rated tubes like the 8873/4/5, et cetera. For
tubes like the 572B and 3-500Z, the first anode resonance -- which is
typically 100 to 160 MHz -- is more likely to be problematic.
>
>Maybe... but it isn't directly relevant to this thread which is
>basically about the network itself, not how you'd use it.
>
>>>In other words, the significant difference between the two
>>>types of suppressor is not at VHF, where their performance can be made
>>>almost identical. The main difference is at HF.
>>
Not according to Wes' measurements.
-Identical? The VHF performance of conventional suppressor can be made
far superior to that of a resistance-wire suppressor -- with one
trade-off.
>>Contrary to other comments, I could not measure any meaningful power
>>difference between either type on 10M in either a SB-220 or a TL-922.
>>Have you run any actual tests at power Ian?
With a Bird digital wattmeter, you should be able to see the difference
-- provided that the person who constructed the parasitic suppressors
used enough inductance to produce a maximal level of dissipation in Rs at
29MHz.
>>Another point that disturbs me greatly is that the AG6K suppressor in
>>the N7WS article does not come even close to matching what is shipped in
>>Rich's kits or in his 2-11-96 5 page flyer. Rich....am I
>>missing something basic here??
>>
- No tube-type was specified for the N7WS measurements. I sent Wes some
materials and a silver-solder kit. Wes constructed a suppressor that was
semi-similar to the W8JI suppressor. . The suppressor Wes constructed
resembles our 572B suppressor specifications, but with less inductance
than we specify.
- For a fair comparison, the suppressors should have had equal amounts
of Ls and Rs. At 100MHz: the W8JI suppressor had 101nH, the
resistance-wire suppressor Wes made had 75nH. Even with the W8JI
suppressor's advantage of 9% more Rs and 33% more Ls, the
resistance-wire suppressor exhibited 46% less Q and 40% less Rp.
>As far as I remember, the suppressors were supplied to Wes by Rich and
>by Tom. The surprising thing is that the measured parameters ever came
>CLOSE enough to allow some comparison.
>
>> IMO, this appears to throw a big WHOA into the discussion. Just what did
>>Wes measure???
>>
>>At this moment I think we need to consider a new evaluation from a less
>>involved and seemingly biased source. I would suggest a test at the ARRL
>>lab that is witnessed by at least a representative of both sides.
In 1994, I wrote *QST* Editor Mark Wilson a letter suggesting that the
ARRL could settle the issue by measuring the VHF performance of the two
types of suppressors in the ARRL Laboratory with an RF Impedance
Analyzer. Mr. Wilson did not respond. At this point in the donnybrook,
in light of the two somewhat less than truthful statements Mr. Wilson
made in the February 1996 *QST*, it seems unlikely that Mr. Wilson has a
potential for zero bias.
>Well, Wes originally was such a source - just a guy who offered to help
>because he had access to the equipment and was an uninvolved party.
Wes was involved in the suppressor debate because he had already stated -
as had Mr. Rauch - that he could design a copper-wire suppressor with any
VHF Q he desired simply by tinkering with Ls and Rs -- which is quite
true *IF the 29MHz dissipation in Rs is not a consideration*.
- It seems likely that Wes eventually understood the Rs dissipation
problem because he never came up with the values for such a suppressor.
In any event, Wes seemed like the right person to make the measurements.
He had the test instruments, we were not related by blood or by marriage,
he had the technical ability, AND he had already taken a
Rauchian-position on the issue at hand - so Mr. Rauch had no means
whereby he could cry foul after the results were published.
Why hasn't Mr. Rauch said why he cancelled his 28 November 1996 post to
the rec.radio.amateur.homebrew NG? ........ The excursion down the
wide river in North Africa seemingly continues.
Rich---
R. L. Measures, 805-386-3734, AG6K
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