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RE: sidebands of CW signals



High Efficiency Linear Amplification by Parametric Synthesis or
HELAPS as it is called by its inventor, Karl Meinzer, does not
produce the world's most linear transmitter.  In our case the
IMD is acceptable but definitely present.  No HF transceiver
manufacturer could ever get away with these numbers.  We
achieve tremendous efficiencies using this technique.  Do you
recall "plate modulated finals" in AM transmitters?  This
technique is not unlike that.  The "phase" and amplitude
information are split along two separate paths.  The phase
channel is hard limited and then amplified through a chain
of Class E amplifiers.  These are unbelievably efficient. I
did not believe the initial numbers the first time I heard them.
At the last stage, the power supply is modulated to reapply
the amplitude information to the last stages.  Karl did a
brilliant analysis that showed for a few different signals
in our pass band that the statistics of the signals rapidly
become nearly ideal (ideal enough for our purposes) and that
this technique was linear enough for us.  Listen to AO-7
Mode B to hear the first in orbit incarnation of this technique.
But just as a thought experiment, think about knowing every
stage of your transmitter design well enough to know how to
"re-phase" or resync the envelope to the hard limited phase
channel and minimizing the differential group delays etc.
which lead to distortion.

Bob N4HY




-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of Wayne Estes W9AE
Sent: Wednesday, July 30, 2003 09:35
To: amsat-bb@AMSAT.Org
Subject: [amsat-bb] sidebands of CW signals


I often hear weak sidebands of strong CW signals on AO40.  The sidebands are
2-3 kHz away from the strong signal.

Would that be a sideband transmitted by the CW station, or is it a
distortion product of the transponder?

Wayne Estes W9AE
Mundelein, IL, USA


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