[GreenKeys] RATT with modern gear

[Nick England]

RATT Problem with newer gear-
Duncan K2OEQ was going to join in, but couldn’t transmit. His ST-6 uses
crystal generated tones. 2125 mark and 2975 space for 850 shift.
Unfortunately his Elecraft has a sharp cutoff at 2800 Hz. His space tone
was down 40dB!

Vintage gear is more hi-fi.
Nick



On Sat, Sep 5, 2020 at 3:21 PM <jvendely at cfl.rr.com> wrote:

> We are using 850 cps shift, mark low, tone center frequency=2 kc, that is,
> MARK=1575 cps, SPACE=2425 cps.  These are common MIL FSK tone parameters as
> used on, for example, the MD-522 modem.  So far, we've been using 7087 kc
> (USB radio virtual carrier frequency), which with the above tone parameters
> places the FSK tones center freq. at 7089 kc.
>
> Best receiving setup (for receivers such as RA6790/GM, RF-590, R-390A,
> etc.) is to use 1 kc IF BW, BFO offset to - 2kc, and tune receiver to 7089
> kc.
>
> For a USB transmitter with AFSK tones as described above, set virtual
> carrier freq. to 7087 kc.  If using amateur-type equipment, which typically
> have narrower IF filters, you may have to reduce the tone center freq to
> keep the SPACE tone from being rejected by the IF filter, and offset the
> virtual carrier frequency to compensate.
>
> Hope you can join the fun.
>
> 73,
>
> John K9WT
>
>

-- 
Nick England K4NYW
www.navy-radio.com
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