Or would the "zero-ohm" load absorb most of the harmonic ?
( a case for a high-pass filter terminated into a dummy load ? )
Don WA4NPL
Quoting "David Cutter" <d.cutter@ntlworld.com>:
> Jim
>
> Thanks for the tutorial.
>
> I've often wondered about the movement of energy in and around a stub.
> Harmonic energy is delivered from the PA to the output feeder and onwards to
> the stub. Would I be right in saying that the harmonic energy is reflected
> from the stub back to the PA where it is absorbed in the output filter? If
> so, this energy is absorbed as heat, it has to go somewhere. Does any of it
> get back to the output device? A pi output filter is a low pass filter in
> either direction, so, I'm guessing that harmonics are mostly absorbed there,
> but is there much attenuation in that direction?
>
> David
> G3UNA
>
>
>> On Tue, 30 Mar 2010 09:19:15 -0400, Carl wrote:
>>
>>> Those are fairly common for multi TX stations to knock down harmonics and
>>> phase noise.
>>
>> Yes. I'm currently working on a Q&A style tutorial on coax and stubs. The
>> first draft is at http://audiosystemsgroup.com/Coax-Stubs.pdf
>>
>> Comments are appreciated. I would especially appreciate additions to the
>> table of amps and output circuits.
>>
>> W2VJN's book is excellent, and worth the money if you're doing any sort of
>> multi-transmitter station. Available from Inrad (the crystal filter
>> people)
>> for $20. There are also four excellent pieces in QST written by Ward
>> Silver, N0AX. They are cited in my tutorial. And George has contributed
>> some of his work on stubs to the 2010 ARRL Handbook.
>>
>> As to the effect of a stub on the current waveform -- a proper stub (or
>> combination of stubs) should be invisible at the TX frequency, but a short
>> circuit at even order harmonics. If the amp has reasonable output
>> filtering
>> without the stub, the stub should have no significant effect on that
>> current waveform.
>>
>> 73,
>>
>> Jim Brown K9YC
>>
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