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:[email protected]] On Behalf Of Fred Jensen Sent: Friday, December 23, 2016 4:38 PM To: [email protected] 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 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
