[Elecraft] PSK31

[Charles Greene]

Don, David and all,

If you use the macros used by Julian, G4ILO, you separate the transmit and 
receive frequencies and avoid "walking up or down the band."  Julian is 
using MixW (written up in August QST), as I am using.  I use the same 
concept as Julian, but also replicate the buttons you need to push on the 
K2 to keep the "fine RIT" on.  I will send the entire set if anyone has 
interest.

The concept of using the upper, middle and lower parts of the bandpass is 
interesting and is unique.  I use this technique on SSB but not on the 
digital modes.  However I agree with Don that there is potential for wide 
separations in receive and transmit frequencies.  It doesn't make any 
difference in SSB and little in CW, but you need a work-around in PSK31 for 
even a small shift in frequency, as Julian is using.  As for the frequency 
to use, I looked at the output of the K2 on OP1 and found there is a dB or 
so ripple in the filter, so I picked a frequency where there is a peak in 
the filter as the frequency to align to, as that is where the S/N ratio is 
best for weak signals when you use FL1.  Actually it made a noticeable 
difference in S/N ratio.  Then I used a noise generator and Spectrogram to 
align all my narrow filters to this frequency.  The freq I use is 1000 
hz.  You can change it by BFO setting, but when you change the BFO setting 
on FL1, it changes the filter shape too.  I have the BFO setting on FL1 set 
so it is the flattest possible.  (Follows bitch about the filter ripple, 
posted before).


"Reply-To: "Don Wilhelm" <w3fpr@peoplepc.com>
From: "Don Wilhelm" <w3fpr@peoplepc.com>
To: "DAVID POWELL" <dwpowell68@msn.com>, <elecraft@mailman.qth.net>
Subject: Re: [Elecraft] RTTY Mode Filter Settings for PSK31 (Correction)
Date: Mon, 21 Jul 2003 16:29:51 -0400

David,

The concept is good, but the implementation has one 'catch' --
This is really 'SSB' mode, and the K2 will use the FL1 BFO when it
transmits.  I havn't worked out all the consequences yet myself (a soon but
future project), but I do feel I should caution you about the potential for
ending up with the transmit and receive frequencies several hundred Hz apart
(the difference in your BFO frequencies).

Long time ago, I did ask Wayne about 'locking' the BFO between transmit and
receive for the RTTY modes, but he chose not to implement it -- at least we
did get the option to turn the compression to 1:1 automatically!!!

73,
Don W3FPR

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

[I see that in my original message I had typed a couple of the BFO
frequencies wrong, so I'm trying again.]

I am experimenting with filter settings in the RTTY/Data Mode (r bar) =
for use with PSK 31.

My objective is to prevent a strong signal at one end of the waterfall =
display from activating the receiver AGC to the extent that I can't copy =
a weak signal at the other end of the waterfall.

My approach is to configure the four "r bar" filter bandwidth and BFO =
settings to provide one setting that covers the full waterfall bandwidth =
(about 350 to 2400 Hz) then three settings that each cover the waterfall =
in overlapping segments. My initial filter settings are as follows:

FL1:  OP1 bandwidth, BF1 at 4916.30 kHz (covers entire waterfall)
FL2:  1.20 kHz, BF2 at 4914.67 kHz (covers lower third)
FL3:  1.20 kHz, BF3 at 4915.39kHz (covers middle third)
FL4:  1.20 kHz, BF4 at 4916.10 kHz (covers upper third)"


73, Chas, W1CG
K2 #462B