Re: Sideband Production

To: tesla-at-poodle.pupman-dot-com
Subject: Re: Sideband Production
From: Tesla List <tesla-at-stic-dot-net>
Date: Mon, 24 Mar 1997 19:54:55 -0600
Approved: tesla-at-stic-dot-net

Subject: 
            Re: Sideband Production
       Date: 
            Mon, 24 Mar 1997 11:12:03 +1200
       From: 
            "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
Organization: 
            Wellington Polytechnic, NZ
         To: 
            tesla-at-pupman-dot-com


Hi all,
          Since I've stuck my neck out on this one, I will explain 
why the sidebands disappear below critical coupling. The reason is 
simple - the circuits are losing energy (in their resistances etc.) 
at a rate greater than or comparable to, the rate at which energy is 
being transferred from one circuit to another. The trade becomes one-
way in those cases or more correctly, dissipates entirely before it 
can go a second time around. This amounts to maximum transmission 
given the losses but *not* efficient transmission since the primary 
can lose as much as the secondary. This is equivalent to matching a 
sink impedance to a source impedance.
     Efficient transmission is the equivalent to running a speaker 
from a low impedance amplifier source at full power output. For a 
typical audio system, Rsource << Rsink except in amps that use no 
negative feedback (e.g. some valve amps where the speaker is matched 
to the anode impedance). A switchmode power supply is another example. 
Compare load heating with power supply heating at full power. A 
further example is the mains supply. Another one yet is a modern AM 
radio transmitter where the modulator is actually a switchmode power 
supply. In an efficient power delivery system, the load alone dictates 
the rate of energy transfer.

Malcolm