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Tech Corner

PSK31 in 60 Seconds!


If you are running Airmail with one of the SCS PTC-II multimode digital controllers then you are about a minute from being on PSK31. Using the PTC-II and a basic terminal program will be "bare-bones" but will work well enough to see if you like the mode.

The following assumes that you have a working Winlink/Airmail setup using a SCS PTC-II mdc :

Bring up Tools..Dumb Terminal . . . from the Airmail main screen

Turn on the PTC-II then Enter to autobaud if necessary

Type RESET

Type PSKT

Tune your radio to a PSK sub-band (try 7070 USB or 7073 LSB) and set the radio tune rate to smallest step possible. 1 Hz is great, 10 will work,  >10 won't.

To receive, tune radio to a PSK31 signal slowly to center the 3 or 4 green lights and when the outer LEDs flash red, you are on. (If you don't have 1 Hz tuning, use Ctl L and K to tweak the frequency DSP decoder by 1 hz to center the green LEDs.)

Use Ctl-Y to transmit then Ctl-Y again to go back to receive.

This will get you on the air. Do a bit of listening and then try a QSO. Have fun.

Notes:

HyperTerm (comes with Windows) is better than Dumb Terminal (comes with Airmail).

There are programs that support the PTC-II in modes such as PSK31. I tried Alpha and Simple, but wasn't impressed with either. I like PA0NC's NcWinPtc better.

To specify a net frequency for PSK31, state the center frequency. Which sideband you use (USB or LSB) doesn't make any difference; e.g. 7070.000 USB with a 1,120 Hz trace is better stated as 7071.120 center frequency.

If you have to remove the PTC to radio connection to eliminate distortion when talking on SSB you have RF getting into the mdc and you need to fix it.

If not already done, set the power out to a nice low level (10-25 watts) . ( Return to the cmd: prompt and use FSKA- My 706 likes FSKA 125 for 10 watts out.). Setting the PSK31 power this way has the advantage of not requiring a reset when you return to voice.

See the PSK31 chapter in the SCS book for the rest of the commands you could use. Ctl-N is useful to turn off frequency tracking in a "Net" environment. Be careful with Ctl-B because it can switch you out of the BPSK mode.

You can change the center frequency set point of the PTC using TONES 2. (Center freq = (MARK+SPACE)/2 . I have mine set for 600 hz so I can use the narrow IF filter in my IC-706.)

Most people use one of the several good sound card implementations of PSK31. Many have "hot keys" and a nice FFT "waterfall" display that shows all the signals in the bandpass and allows you to tune around with the mouse. I like Digipan. MixW is popular.

You can buy a computer sound card to radio interface, but it's easy to make. You will need a pair of small 1:1 audio transformers and a 4N27 optocoupler. I can share my design but it's pretty much standard. If you are using a notebook, watch for hum output 120hz from the radio dial frequency when the battery is low and the ac charger is on.

Other modes to try with the PTC-II using the same setup :

Baudot RTTY
Linked Amtor
Amtor FEC
Pactor FEC
Non- Winlink Linked Pactor
Sitor FEC broadcast receive (NAVTEX in raw mode)

If anyone would like a schedule to try any of these, let me know.

73, George, W4AVO
george@w4avo.org

2/07/06

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