I understand that advice, and follow it most of the time.
However, I found that when I was trying to receive weak PSK31
signals, strong, nearby signals would make decode impossible.
Using a combination of the 250 Hz filter with the DSP filter,
sometimes as narrow as 50 Hz would allow decode. I think the
problem was that the combination of the strong signal and the
weak signal exceeded the dynamic range of the audio AtoD
converter going into the computer, and the weak signal lost out.
I could be wrong.
This problem occurred with a SignaLink. I have not had as much
of a problem with the KIO3B running FT8, but the circumstances
are different enough between the two modes that I'm not sure
that is an apples to apples comparison. I was able to improve
FT8 decode through the KIO3B when there were strong signals 2-3
KHz away from the FT8 subband by narrowing the DSP bandwidth
from 4K to 2.5K (which automatically switched from the 13 KHz FM
filter to the stock 2.7 KHz filter).
73 Bill AE6JV
On 3/8/18 at 8:38 PM, j...@audiosystemsgroup.com (Jim Brown) wrote:
On 3/8/2018 1:08 PM, Bill Frantz wrote:
I got the 250 for eliminating loud PSK signals from wiping out
weak ones. It was a bunch of playing with center and width,
but worked quite well.
Hi Bill,
Recall my post from a few days ago about phase shift being the
enemy of signal decoders, and that filters built with real
components (and most digital domain filters) create phase shift
in the passband. The steeper the skirts, the greater the phase
shift, and the more it extends into the passband.
I don't work PSK31 and don't know about PSK31 decoders, but the
authors of other decoding software (WSJT-X, 2Tone) recommend
that radios use wide bandwidth and let the decoder reject
off-frequency QRM. Heavy duty RTTY guys like W0YK recommend 500
Hz for RTTY, and K1JT recommends the full bandwidth of SSB
channel. I follow their advice, and find it works well for me.
73, Jim K9YC
-----------------------------------------------------------------------
Bill Frantz | Can't fix stupid, but duct | Periwinkle
(408)356-8506 | tape can muffle the sound... | 16345
Englewood Ave
www.pwpconsult.com | - Bill Liebman | Los Gatos,
CA 95032
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