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 --Northern California Contest Club --CU in the Cal QSO Party --7-8 Oct 2017 On 12/23/2016 3:46 PM, Ron D'Eau Claire wrote:
The fact that the RF amplifier is running Class C should not be an issue if it is plate-modulated. Plate modulation is the "gold standard" because only the RF carrier is being amplified in the Class C stage. Beyond that its non-linearity is employed to mix the modulating signals with the RF carrier. While the process is extremely linear, it takes a lot of audio level power - at least 1/2 of the RF carrier power. Fred's observation makes me think WWV may be using some sort of "compromise" system such as grid modulation rather than plate modulation. Much lower audio (baseband) power required, but it is not as linear either. 73, Ron AC7AC
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