[Elecraft] Elecraft gear relative IMD

[Jim Brown]

On Thu,12/31/2015 4:34 AM, Kevin Stover wrote:
> IMD is not regulated 

It is, as part of the wording of regulation of transmitted bandwidth, 
but the wording doesn't include numbers. The regulation states (I'm 
paraphrasing from memory) that the bandwidth of the transmitted signal 
shall be no greater than required for the means of transmission. I've 
served on the AES Standard Committee, and that's the sort of language 
used to say that the signal should be as narrow as possible, but that it 
is understood that through the years, it will be possible to make 
narrower rigs, so it leaves out the number, which is a moving target.

Elecraft has pretty well set the standard for the bandwidth of a CW 
signal, thanks to the careful control of the keying waveform, pretty low 
IMD, and a design architecture that produces very low phase noise. In my 
tests, I see the K3 as no cleaner than other rigs I've tested on SSB, 
but significantly cleaner on CW, RTTY, and digital modes.

Important note: IMD strongly affects the bandwidth of a CW signal, 
because CW is 100% amplitude modulation of a carrier by a square wave. 
Square waves have an infinite number of harmonics, the strength of which 
are related to the rise time of the CW keying (and NOT to CW SPEED). The 
IMD of a gain stage that amplifies that signal WILL produce sidebands 
(clicks). CW keying bandwidth can easily be measured using a spectrum 
analyzer that has low enough resolution bandwidth. A P3 can do it, and a 
P3 with SVGA has even lower resolution bandwidth. Likewise, an SDR with 
suitable software can do it, and I'm planning to buy an ANAN 10E for 
measurement only.

But the FCC Rules make the operator responsible for occupying the 
minimum spectrum. So that means buying a rig that's clean in the first 
place, giving the rig enough DC voltage, and not overdriving audio 
stages and power amps.

73, Jim K9YC