[TenTec] ARRL Phase Noise Data Plotted to 1 MHz

[Jim Brown]

On 7/27/2014 10:27 PM, Jim Brown wrote:
> Off list.

Well, I meant to send it off list, but it was late. :)

>
> I've been thinking about this. 

Overnight, I thought some more.

The keying waveform is, fundamentally, modulation of a continuous 
carrier by a waveform that approximates a square-wave -- hence the name 
CW for continuous wave. ANY square wave has an infinite number of 
harmonics, the relative strength of which depend primarily on the shape 
of the switching waveform from on to off and off to on. The faster the 
rise time, the more harmonics, and those harmonics will be stronger. 
Those harmonics show up as sidebands, and the higher the order (harmonic 
number), the farther they are from the carrier. In a rig without IMD, 
that would be the end of the story, but real amplifiers have IMD, so 
those harmonics produce IMD, which results in more sidebands.

Rigs with cleaner keying reflect the skill of the designer to minimize 
the harmonic content of the keying waveform, the level of TX IMD, and TX 
phase noise.

Close to the carrier, the key click spectra plots pretty much tell the 
whole story of what the TX is doing, because they include the effects of 
the keying waveform, phase noise and IMD.  As we listen farther off 
frequency from the transmitter, all that's left is phase noise.

73, Jim K9YC