The key to setting these filters is to understand what is being used to
generate the RTTY or AFSK tones. In my case, a KAM, as I indicated
initially, was used for RTTY. This means that the KAM must be fed 2125Hz
tones from the K2, then shift down if RTTY normal and up if RTTY reverse by
170 Hz. Don, W3FPR, gave me a clue when he indicated I should set the
markers in Spectrogram at 400 and 2400 and place the RTTY filter using CAL
FIL and Band- to get to the BFO setting. Doing this allowed me to receive
RTTY tones with OPT1 filter in the RTTY position. I then proceeded to set
the width of FL2 and adjust the BFO, again centering the display in
Spectrogram around 2125 or, put another way, placing the filter display so
that it covered all frequencies of the RTTY tones for proper input to a KAM.
I then set filter 3 and filter 4 in the same way.
I selected OPT1 for FL1, 1500Hz for FL2, 800Hz for FL3 and 450Hz for FL4. I
found in each case I needed to readjust the BFO setting for filters FL2
through FL4. I also found that 450Hz is mighty tight for tuning with a KAM
but I sat here listening to a RX3 call CQ. Thank goodness his signal was on
as it eased my problem of setting the filters.
The key is a KAM TNC and the tones it must see. Other programs, like MMTY
or others, allow much more flexibility in where to set the center of the
RTTY filter passband. If I go to MMTY one of these days, I will have to do
this exercise again but at least I know am confident in setting the filters.
Hope this helps someone struggling with setting RTTY filters for use with an
external TNC.
73,
Charlie, W0YG..>>
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