[Elecraft] FSK on a K2?

[Fred Jensen]

Ron D'Eau Claire wrote:
> So the way to do FSK on a K2 is to develop audio tones within the normal
> voice bandpass of 300 to about 2.1 KHz whose separation is equal to the
> shift you need in frequency. Apply those to the K2's mic input and it'll
> produce a shifting RF output or FSK. Today, those tones normally come from a
> PC or special controller of some sort. 

You want to make sure the source of the audio tones [e.g. soundcard] is 
producing two pure sine waves with no harmonics or other noise.  A 
non-sinusoid audio tone will have other audio frequencies in its 
spectrum, and each of those will produce an additional RF signal offset 
from your suppressed carrier by its audio frequency.  A common source of 
noise in the audio output of a soundcard comes from the switching power 
supplies that power laptops.

I ran my K2/100 at 50W driving my LK-5002C amp to about 500W in the ARRL 
RTTY Roundup, and it was a fantastic rig.  It takes a little while to 
get the filters set up with CAL FIL, but once done, the real power of 
the K2 RX really shows up.  I'll be back in the WPX RTTY coming up on 
9-11 Feb.

And be careful ... RTTY is continuous duty when transmitting. At 50W, 
the KPA100 heatsink got uncomfortably warm when I was in a good run and 
transmitting nearly full time.  I wouldn't advise running more than half 
rated power [7W for a K2, 50W for a K2/100] when running RTTY.

73,

Fred K6DGW
Auburn CA CM98lw