[Elecraft] Data mode and filters

[Jim Brown]

On Mon,5/11/2015 6:45 PM, Joe Subich, W4TV wrote:
> The K3 may be cleaner than low end 12V/100W rigs like the Icom 706mkIIg
> 7000, 7100, Yaesu FT-450/991, etc. but it is certainly *not* as clean 
> as the other top of the line contest rigs like the Icom 7600/7800,
> Yaesu 2000/5000, Kenwood 990, etc.  For example, ARRL measured the K3
> at -29/-43/-46/-51 dB vs. -32/-49/-52/-54 dB for the Icom 7800 and
> -31/-46/-54/-57 dB for the TS-990.  That makes the K3 3 to 6 dB *worse*
> than other top of the line rigs at rated output.

But Joe, you are fixating on a single specification, which is only one 
part of what establishes the cleanliness of a radio. On CW and FSK, 
there is the keying waveform, and on all modes there is phase noise. The 
K3 rise time for both modes is quite well controlled, so the keying 
transients that excite IM in those other radios don't excite IM in the 
K3. And phase noise in the K3, even before the new synth boards is close 
to the best of any modern radio.

The occupied bandwidth measurements show the SUM of all these 
mechanisms.  I've been using pink noise for SSB spectrum measurements 
because the signal excites IMD in a manner similar to what a voice 
would, and I've made measurements with me talking into a live mic. 
There's no significant difference between the live mic and the pink noise.

The FTDX5000 report to which I posted a link shows that the K3 and 
FTDX5000 have almost the same occupied bandwidth on SSB, but the K3 has 
10 dB of signal processing. AND -- my K3 is even narrower because I've 
cut everything below about 400 Hz with TXEQ. If you missed the link, 
it's on my website.

In many contests, I've got a CQ machine 8 miles from me with a 7600 and 
a legal limit amp who regularly wipes out 5-10 kHz on CW, but K6XX, only 
3 miles away with a K3 and ancient tube amps is only 700 Hz wide at -50 
dBC. The 7600 and 7800 tested quite similarly in bandwidth tests by ARRL.

Six months ago, when I began doing my own measurements with a P3/SVGA, 
you insisted that the IMD in a K3 would make a mess of PSK31, so I 
measured PSK31 signals. They are in the set of P3 measurements I have 
posted here several times, and they clearly show that you were wrong!  :)

For those who missed the link, the measurements, as well as a 
description of my test setup, are on my website. k9yc.com/publish.htm

73, Jim K9YC