[Elecraft] IMD and CW

[Fred Jensen]

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
>