AFSK 1200 Modem 1200 Baud
for Packet-Radio Controller TNC3/31

Users manual (english)


The AFSK1200 modem is made for use with TNC3S or TNC31 packet-radio-controler. The pc-board has the dimensions 120x40 mm and it can be connected wit a 20 pin flat ribbon cable to TNC3 or TNC31. The trimmers (DCD-PLL, microphone-output, demodulator-trigger) can be accessed through the window on the rear panel of TNC3. The radio is connected with a 5 pin DIN plug as usual with every TNC2.


The modem uses a crystal controlled modem-IC, all frequencies and the baudrate are derived from a single quartz oscillator. The AFSK1200 is supplied with 5 V DC, approx. 20 mA. The carrier detect circuit (DCD) is done separately with a XR2211 tone-decoder IC. DCD-status is displayed with a LED "DCD" on the front panel. The modem is muted when receiving. This makes it possible to connect more than one modems parallel to a common transmitter / modulator. Transmitter keying (PTT): Open drain  VMOS-FET for max. 0,2A PTT current. Continupos transmit time is limited by a 20 sec. watchdog timer. The AFSK1200 modem is capable for full duplex operation (simultaneous transmit + receive).


You can download the english language manual here. It includes instructions to connect all common transceivers and explains operation, settings and adjustment of the AFSK1200.

Ordering Information AFSK1200 1200 Baud Modem

Usually, the AFSK1200 is already installed in the TNC3S or TNC31. When ordering separate AFSK1200, we ship the tested complete board with an extra manual.

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