[Elecraft] Data mode filters

[Don Wilhelm]

> Can anyone comment on the proper way of setting the data mode filters?


 Samuel,

The 'proper' way to set the data mode filters depends partly on the data
mode that you want to use.
If you are using the computer soundcard to do the decoding, most of these
programs work FB with the normal SSB filter which has the advantage of less
passband ripple than does the variable bandwidth filter when used at wider
bandwidths.

No matter which filter you chose for data mode, you want to be certain the
audio tones for that particular digital mode will fit within the passband
(vary the BFO setting to accomplish that).  Spectogram will be handy to set
things up and if your choice is to use a narrow filter, it may be essential.

For RTTY, the audio tones to be decoded are 1445 and 1275 Hz for 170 Hz
shift RTTY.  So you want the passband to be enough greater than 170 Hz so
tuning the receiver onto the signal will be not critical (I would suggest
400 to 500 Hz bandpass width).  Then you would set the BFO so that both the
1275 Hz and 1445 Hz audio tones are well within the passband as viewed on
Spectogram.

For PSK31, the procedure is similar, but most folks simply use the normal
SSB filter and let the software and soundcard do the audio filtering.  You
can use a more narrow filter setting to achieve a better S/N ratio, and if
you chose to do that, just decide how narrow a bandpass you wish to work
with and at what audio frequencies and follow the same procedure as for RTTY
above.  If I were to make those choices for PSK, I would create a passband
from about 800 Hz to 1200 Hz (400 Hz) - but that is just my personal
choice - you can pick anything between about 300 Hz and 2700 Hz and
accomplish the same thing.

Good luck with it,
73,
Don Wilhelm  - Wake Forest, NC   W3FPR home page: http://www.qsl.net/w3fpr/
  QRP-L # 485   K2  SN 0020   mailto: w3fpr@arrl.net