[Elecraft] IMD and CW

[Ron D'Eau Claire]

Not in my experience as a broadcast engineer in the 1950's. Class C
amplifiers, plate modulated, were the standard low distortion transmitters
for decades, just as they were used in the best A.M. Ham rigs like the
Johnson Kilowatt. 

But, as the big commercial stations came on the air running 50 kw the
scramble was on to find an alternative to having an audio amplifier that
could produce a full 25 kw of clean audio to modulate them, requiring a
modulation transformer the size of one of the huge transformers at the local
power mains distribution center. That is when, IMX, all sorts of alternative
schemes for modulation, all of which were less "clean" (although still very
good when handled correctly) came into use. 

Stations chose more complex and careful adjustment during operation than
investment in hardware and facilities. But, after all, in the US the station
had to have a broadcast engineer monitoring the transmitter at all times,
logging critical readings every half hour. 

73 Ron AC7AC

-----Original Message-----
From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Fred
Jensen
Sent: Friday, December 23, 2016 4:38 PM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] IMD and CW

This has drifted fairly far from the original.  Thus encouraged ...

I wondered about that and being retired I pursued it, ultimately with the
tech folks [well, one folk] at WWV who repeatedly assured me that they were
on-frequency and that their time information was correct which of course was
never the issue.  Somewhere in all the words I read about the station, I did
find a reference to plate modulated Class-C transmitters but I have lost
it's QTH on this disk drive.

Most plate modulators ran Class-B or -AB, and were subject to cross-over
non-linearities.  The 5, 10, and 15 MHz signals look very much the same on
the spectrum display which [weakly] suggests the unexpected distortion
products may arise somewhere in the baseband chain.  The 2.5 and 20 MHz
transmitters, being low-level modulated, may tap that chain before the
distortion is introduced.

ARC-5's, when cathode-keyed, were notorious for key clicks, almost as bad as
the Yeasu rigs of recent eras. [:-)  Of course, for my K3, the
"carrier-balance" and "opposite sideband suppression" is perfect.  I think,
but don't know, that the K3 shapes the CW with a raised-cosine filter.  With
strong signals, it *is* possible to identify a K3 by its CW spectrum,
particularly in the WF.

Fred K6DGW
Sparks NV DM09dn
Washoe County