[RTTY] IARU and 14100 Beacon QRM from Digital Signals

[Bill Coleman]

On Oct 1, 2006, at 9:15 PM, John Becker wrote:

> If you dial says 14,002 both your mark and space will be out of
> band.
>
> this I don't understand -  "I myself use 1415 and 1585" - are
> you saying that you tones are 1415 and 1585 ? If so I will never
> ever be able to copy you signal.

Sure you will. Say I'm calling CQ and my radio dial reads 14.081.50.  
Since I'm using AFSK and LSB, my mark signal will be 14,081,500 Hz -  
1415 Hz = 14,080,085 Hz. The Space signal will be 170 Hz lower, at  
14,079,915 Hz.

You're using AFSK tones of 2125 and 2295. You tune me in one your  
radio. Since your tones are different, your dial will read a slightly  
different frequency: 14,080,085 + 2125 = 14,082,210. So you'll see  
14.082.21 on your radio.

We're both on the same frequency, because our mark and space signals  
are on the same frequency. Our radio dials will just read differently.

(I chose 1415 and 1585 carefully because of the limitations of the K2  
RTTY mode. To use the DSP module, the center frequency must be a  
multiple of 100 Hz. I wanted to pick something high enough so the  
second harmonic didn't fall into the SSB filter passband. It also  
needed to be low enough that the K2 BFO didn't run out of range as I  
adjusted the variable bandwidth filter. A center frequency of 1500 Hz  
worked out well.)

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901