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 ______________________________________________________________ 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]
