On Mar 20, 2006, at 1:04 PM, k8rs wrote:
> Now, I would like to know the
> latest and best suggestions on the RTTY filter widths and which
> frequency markers to insert on Spectrogram. Do you use two markers
> 170 Hz apart?
Depends on the software you are using. You can use the "low" tones of
1275 and 1445 Hz, or the standard tones of 2125 and 2295, or you can
use anything in between that is 170 Hz apart, with the Mark tone
being lower (assuming you use LSB, which will make the mark tone the
higher frequency transmitted). Whatever your software would allow.
The problem with using the higher tones with the K2 is that you may
not have sufficient BFO range to program both sidebands correctly
without modifying the BFO. Increasing the BFO range will reduce the
precision of each step, so it may make it harder to get all the
filters aligned to the same frequency.
When I modified my K2 for RTTY, I ended up choosing 1500 Hz as the
center frequency (mark of 1415 Hz and space of 1585 Hz) My reason for
choosing this instead of the low tones is that the second harmonic of
the low mark tones (2550 Hz) would be on the edge of the SSB passband.
The other reason was so I could program the KDSP2 for RTTY. It
doesn't allow the user to choose anything but 100 Hz increments for
the center frequency
As it was, I ended up changing the BFO circuit to get enough range. I
added caps to C173/4 (I think that's right), but didn't get quite
enough range. A 2 pf cap across one end of the crystal to ground
fixed that. This mod is documented in the archives.
Bill Coleman, AA4LR, PP-ASEL Mail:
[hidden email]
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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