[GreenKeys] Filterless TU

[Richard Knoppow]

    850 Hz shift was the old ham standard.
    RTTY was sent via CW at one point. Frequency shift has a 
large advantage in effective power. I am not sure I am 
remembering this right but I think its about nine db.
    Using the MARK frequency as a CW mark signal will work. Some 
FSK converters use separate filters for mark and space but an FM 
detector can also be used. Each has some advantage. The FM type 
detector can be made to work for any shift within its range but 
has the same characteristics as an FM demodulator for voice, 
namely that it has a sharp noise threshold and lower output as 
the amount of FM is reduced.

On 9/16/2019 1:29 PM, Ralph Mowery wrote:
> Looking at the schematic, I just wonder if it is made to work with a narrow filter in the receiver and the older 870 hz shift.  The receiver would be set so that only the space tone would pass through the receiver filters and really make it like on and off keying.  There is a circuit in the 1966 ARRL handbook that shows a one tube circuit that does this.  The mention setting the BFO to zero beat with the mark frequency so only the space frequency makes it to the converter.
> 
> A local ham told me he built that converter many years ago and it did work on good signals.
> 
> Ralph KU4PT


-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL