[Elecraft] K2 & PSK-31

[Julian (G4ILO)]

Rod,

I take it you don't have the KIO2 installed, nor the updated firmware?
Otherwise I'd enable the RTTY mode, which allows you to set up separate
narrow filters optimised for data, and also disables the compressor.

If you are forced to use USB or LSB, then you want to disable compression
(SSBC). The SSBA setting can stay the same is it usually is: the trick is
to make the attenuator in the cable from the computer to the mic socket so
that it generates about the same level of audio as your microphone, then
you can fine tune the audio level using the computer mixer settings. If the
power is quickly jumping from 0 to 5 watts as you advance the slider from
zero then I guess either you don't have an attenuator at all, or its effect
is too small, or possibly RF is getting in to the microphone socket. I
can't remember the value resistors I used in my attenuator, unfortunately,
but I guess they won't be far different from the values recommended by
G3PLX in the help file to his original PSK program, which is 100K in series
with the audio and 1K down to ground.

Unfortunately, I don't think it is possible to use VOX to control the TX/RX
switching in the K2. In my experience, the K2 VOX is too insensitive, with
the result that you have to set the audio input too high for a clean signal
in order for the VOX to trigger. (BTW, I'd really love to see a KSB2 MkII
with greater input sensitivity and a more sensitive VOX.) There's really no
excuse for not using DTR or RTS to control the PTT, as the circuit only
involves one resistor, one general purpose diode and one general purpose
NPN transistor and can easily be built to fit inside the D-shell on the PC
serial port.

If you have done the KI6WX modification to the KSB2 then one ALC bar is
acceptable for a clean signal. Prior to that, I used to set the K2 power
control to 10 watts and then control output power entirely using the
computer mixer settings, so that there was no ALC action at all. I measured
an IMD of -34dB in that configuration, with an output power of 4 watts.

73,
--
Julian, G4ILO. (RSGB, ARRL, G-QRP, K2 #392)
G4ILO's Shack: http://www.qsl.net/g4ilo

Rod N0RC wrote:

Folks,

I read the PSK app note: http://www.elecraft.com/Apps/PSK31_2.PDF but
still have questions about setting the TX audio level.

I'm using a cable as described in the appnote, and I am using VOX (0.4
setting) for TX/RX mode switching; software is Digipan; Pout is set for
5W; SSB A = 2; SSB C = 2:1.

With the K2 in RF out mode: As I advance the soundcard volume the power
quickly jumps from 0 to 5 watts, I believe this behavior is a result of
the tracking ALC of the K2.

With the K2 in ALC mode: As I advance the soundcard volume I can adjust
for 1 ALC bar or 2 ALC bars. I can even set the audio so that the second
bar is flickering somewhat.

Is there a more refined way to set the K2 for good PSK performance?

Based on reports received from others, I believe this config to be
optimal:

    Pout <= 5W
    SSB A = 2
    SSB C = 2:1
    Audio-in level set so that the second ALC bar flickers

Is there something I've not accounted for?

73, Rod N0RC
Elecraft CC: 0 of 100, started 05-Jan-2003