Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!rice!uw-beaver!uw-entropy!dataio!pilchuck!ssc!markz
From: markz@ssc.UUCP (Mark Zenier)
Newsgroups: sci.electronics
Subject: Re: AM Radio
Message-ID: <447@ssc.UUCP>
Date: 31 Jan 90 05:29:30 GMT
References: <90026.012605TRM900@PSUVM.BITNET> <26374@cup.portal.com> <3044@optilink.UUCP>
Distribution: usa
Organization: SSC, Inc., Seattle, WA
Lines: 18

In article <3044@optilink.UUCP>, elliott@optilink.UUCP (Paul Elliott x225) writes:
> Slightly off the subject of the original question (re: improving the
> transmitted frequency response), What _is_ the current practice in AM
> transmitter design?  I am familiar with the classic plate-modulation
> methods, but many years ago studied other methods such as using two
> unmodulated carrier sources, phase-modulating them, and combining them to
> yield an AM signal.  This had the advantages of not needing all the iron
> of the plate-modulation schemes, possibly better efficiency, and better
> fidelity.

One method, describe to me by a station engineer, is to jack up the
voltage by a factor of two and use a second power tube as a cathode
follower switch.  This top tube was switched with a 70 Khz pulse width
modulated version of the audio, and then filtered to provide the plate
voltage for the RF amp.  The filament transformer for the switching tube
must be something special.

markz@ssc.uucp