By the way Jon,
I forgot to mention in the last letter that when I was originally talking
about the 3db down point and the calculations, I was not thinking straight
and I was confusing the voltage divider of the coupling cap and the input
impedance of the next stage. When the coupling cap reactance is equal to
the input impedance, the power is down 3 db or the voltage is down 6 db.
Billy
>From: "Billy Ward" <billydeanward@hotmail.com>
>To: amps@contesting.com
>Subject: Re: [AMPS] Conjugate Matching and Efficiency
To: <amps@contesting.com>
>Date: Fri, 25 May 2001 16:09:10 -0000
>
>
>Greetings Jon,
>
>Again, I must admit that I only have time to skim. There are folks waiting
>to use this computer and I have bout 9 minutes.
>
>
>JOHN:
>At the 3 dB points, half the power that is transmitted at that frequency by
>the source or whatever, gets passed through to the load or whatever is on
>the other side of the filter.
>
>So where does the other 3 dB go? Is it dissipated? Hardly. To understand
>where it goes, one must look at the magnitude of S11 and S22 of the filter.
>At the 3 dB point, the values of S11 and S22 are getting large and all of
>that power is being REFLECTED back towards the source.
>
>BILLY:
>I need to study this further and think on it but I have a problem thinking
>that power can just be reflected back to the source and done away with. It
>has to go somewhere. If we have a conjugate match at a given
>frequency--and
>we can only have a CM at one frequency--then the output will be attenuated
>at any other frequency. Just as we cannot create power, we cannot destroy
>it either. We must dissipate it in a manner that does a job for us such as
>transmitting an rf wave or dissipate it as a loss.
>
>(I believe that this is related to the "law of the conservation of energy".
>It's been years since chemistry so I could be wrong.)
>
>Back to the Tuner instead of the filter:
>
>I have never had the need of thinking this out before but since we are
>discussing the Conjugate Match (rather than a band-pass filter), if there
>is a loss of 3db which, of course, is at a frequency that is close to but
>removed from the CM point, a portion of but not all of that power will be
>re-reflected toward the load. It would seem that some of it must get by the
>re-reflection point of the tuner to the source and a portion of it should
>be
>re-reflected to the load. Does this just continue to go on and on until it
>has made so many trips up and down the feed line that it has dissipated in
>the resistive losses of the line? And what about the part that will get
>past
>the re-reflection point to the source. Does it not dissipate in the
>lossiness of the source output impedance. My main point is that it has to
>go somewhere! I wish I had more time to spend here but I will take the
>file
>with me.
>
>Please re-send yesterdays letter to me privately. I copied it to the
>A-drive and the disk was no good and I have already deleted it from my
>hotmail account.
>
>Billy
>
>Billy
>
>
>
>
>
>
>
>
>
>
>_________________________________________________________________
>Get your FREE download of MSN Explorer at http://explorer.msn.com
>
>
>--
>FAQ on WWW: http://www.contesting.com/FAQ/amps
>Submissions: amps@contesting.com
>Administrative requests: amps-REQUEST@contesting.com
>Problems: owner-amps@contesting.com
>
_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|