[Elecraft] FILTER QUESTION

[Don Wilhelm]

Greg,

I can only give you an indirect answer to your question, hopefully you can
determine where you want to set Spectogram's frequency markers to aid you in
that process.  In fact, part of the answer will depend on the hardware you
are using to decode rtty/psk.  If you are using the familiar computer driven
software programs, it may be adequate to simply use the OP1 filter set as
you would for normal SSB.  If you want better S/N performance and are
willing to accept that you will have to do a bit more receiver tuning as
opposed to just clicking the audio tone bar on the computer screen, you can
follow the steps outlined below.

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

----- Original Message -----

> Hi K2ers.  I downloaded spectogram and want to set the filters for the
> rtty/psk mode (mode r)  mode r LSB for rtty and R USB for PSK.  Where do I
> set the two frequency markers so I can set the noise background properly.
I
> know (think) they should be different for both rtty and psk31.
>