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AN-93 HF Modem

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The AN-93 kit (designed by Johan Forrer, KC7WW) provides any PC user with the capability for operating RTTY, AMTOR, and PCTOR with this simple modem-only design. AN-93 is the equivalent of a BayCom, BayPac, or PMP setup, but for HF digital operations. This very simple kit should be for many that have wanted to play on HF, but didn't want to pay the money for an expensive multi-mode controller.

With the AN-93, only three components are required for HF digital communications: a PC-compatible computer, the AN-93 modem, and software that performs the encoding and decoding. The AN-93 comes with a tuning indicator to allow visual tuning and the unit also provides audio output for oscilloscope display.

  • Modem Specification
  • AGC at > 100-mV audio input amplitude
  • Prefilter bandwidth > 1 kHz
  • Discriminator channel filter bandwidth 120 Hz
  • 170-Hz channel separation
  • Data low-pass filter cutoff 200 Hz
  • Automatic threshold corrector
  • Tuning indicator
  • A/D converter for "soft" error correction

The TAPR AN-93 allows for both FSK and AFSK output, allowing operations on all HF radios. Instead of two separate boards as shown in the QEX article, the TAPR AN-93 single board dimension is approximately 4Sx3.5". The AN-93 operates off 12volts DC. The kit allows for self-tuning and calibration. A Digital VOM and a working PC is needed in order to calibrate and test the modem. Connections to the RS-232 serial and parallel ports are made through DB-9 and DB-25 connectors. Interfacing to the radio is through a DB-9 connector. The kit will be shipped with the A/D convertor providing full-memory ARQ capability for PCTOR.

Shareware software is included along with Johan's code. If you decide to use the shareware software, TAPR requests that you do submit the necessary registration fee.

For a full description of the AN-93 modem and its specification, refer to the May, 1994 issue of QEX and PSR issue #55.


    Forrer, Johan. (1994). AN-93, an HF Modem for RTTY, AMTOR, and Pactor Software. QEX: The ARRL Experimenter's Exchange. May, #147. pp. 3-11.

    AN-93. TAPR, PSR Issue #55. Spring 1994. p. 8.

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