Hi Axel,
full ack with Joe. I use the 400 Hz 8 Pole with a DSP of about 300-350
in dual tone. Perfect!
73!
Frank, DD7ZT
Joe Subich, W4TV schrieb:
After making extensive tests and plotting the selectivity curves
of the 200 Hz filter in my K3, I'm convinced that it is too
narrow for reliable weak signal RTTY operation, particularly in
conjunction with the dual-tone filter.
The measured -6dB bandwidth of the 200 Hz crystal filter was
209 Hz and the composite bandwidth of the 200 Hz crystal filter,
200 Hz DSP and dual tone fitter was less than 170 Hz. A standard
170 Hz shift 45.45 baud RTTY signal needs at least 235 Hz
(170 + 3*22.7) and the dual tone filter represents a 220 Hz (two
50 Hz filters with center frequencies separated by 170 Hz).
After extended discussion with a well know RTTY op and K3 beta
tester, I believe the combination of a 300 Hz 5-pole crystal filter,
300 Hz DSP and the dual tone filter will have a composite -6 dB
bandwidth of about 250 Hz - about optimum for narrow RTTY. The
currently available, "250," "400" or 500 Hz filters in combination
with a 300 Hz DPS bandwidth and dual tone filter are very close to
optimum.
73,
... Joe, W4TV
Hi K3-folks,
What would be the best RTTY roofing filter for the K3? Is the
400Hz 8-pole
filter too small and the 500Hz 5-pole filter the better choice?
Thanks in advance for your answers.
73 de
Axel, DL3ZH
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