>
>Rich Measures wrote:
>
>>>From: Ian White, G3SEK [SMTP:G3SEK@ifwtech.demon.co.uk]
>>>
>>>I used to think that the Q of a parasitic suppressor had some meaning.
>>>having looked at the problem in detail, I don't believe that any more.
>>>
>>? Has standard AC Circuit Analysis been obviated?
>
>On the contrary... but it has been used on the whole circuit, not just
>stopping at the suppressor.
>
? the L-R suppressor can be measured on a Z analyzer. The whole circuit
can not.
>>Has Dick looked at
>>the numbers in Wes' measurements?
>
>The original was from me - Dick was the messenger.
>
>>>The parasitic suppressor operates only on #3 and #1. But in fact the big
>>>unknown is #2, because it depends on the individual design and
>>>construction.
>>
>>? Fortunately, #2 can be found on the mfg's technical specification
>>sheets. It is the tube's internal feedback C from the output element to
>>the input element.
>>
>If that one parameter was truly was all that mattered, you'd be able to
>design a suppressor by theory alone.
? Ca-g or Ca-k does no more that tell one how much output-to-input
feedback capacitance exists inside the tube..
>
>Other unknowns that affect feedback include: the series impedance that
>prevents the common element (grid or cathode) from being completely
>grounded; the impedance of the input side, as seen by the tube at the
>frequency of oscillation; the effects of direct inductive or capacitive
>feedback around the tube; feedback through not-quite bypassed wiring;
>etc, etc...
>
? agreed
>
>>> That's why you always have to develop the suppressor by
>>>cut-and-try methods.
>>>
>>? If R-supp burns out on 10m, the vhf suppressor is out of business.
>
>Ironically, the dissipation at 10m is one of the few things you *can*
>estimate accurately using theory.
>
? agreed. The (exact) calculus is somewhat more difficult. .
>
>>>Finally, the characteristics of the suppressor consist of TWO numbers, R
>>>and X (both of which will vary with frequency... yes, even R). To work
>>>out what the suppressor will do for an amplifier, you need BOTH of those
>>>numbers separately. If you roll the two numbers together and talk only
>>>about a single value of Q, you have just thrown away any chance of truly
>>>understanding what is going on!
>>>
>>? Calculating Q at the anode resonance freq. is throwing away any
>>chance of truly understanding?
>> Q is inexorably related to Rp and Rp is
>>a major determiner of vhf gain.
>>
>If you take "Standard AC Circuit Analysis" ALL THE WAY, you need to know
>both R and X. Their ratio Q doesn't tell you enough.
? Solving R and X to arrive at Q hardly results in the loss of R and
X. When it comes to comparing damping devices, is mo' Q mo' betta?.
>
>>// To me, Dick's dire proscription to
>>ignore Q sounds like what prestidigitators call "misdirection".
>>
>Misdirection is making the audience look at only one thing (let's call
>it Q), while the real action is somewhere else. What I said was exactly
>the opposite: look at EVERYTHING that matters.
? Maybe I'm confused. Was it you or Dick Ehrhorn who said not to look
at Q?
>>
>>- In the Wizard of Oz, wasn't there a proscription to ignore the man
>>behind the curtain?
>
>Indeed there was... but this isn't Oz.
? Whenever someone tells me to ignore something, personal experience
tells me it's time to start paying closer attention. .
>
- cheers, Ian
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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