Technical data

AFSK1201 Seite 2
Preface
This manual should help you to use the AFSK-Packet-Radio-Modem AFSK1201 in your TNC3 or TNC31
controller and to install the connection to your radio transceiver. If there are any problems, you may ask for
help via a-mail at [e-mail].
Technical data AFSK1201-B
Power supply: 5 volt DC, typ 10 mA
Dimensions: ca. Length=120mm, Width=40mm, Height=25 mm, mass approx. 30 grams
Radio interface: 5-pin DIN connector, same pinning as TNC2, TNC2S, TNC2H etc. 1200 bit per second
AFSK (Audio Frequency Shift Keying) 1220/2200 Hz according to Bell 202 specifications.
AF-output level adjustable from 10 mV
pp
to 0.3 V
pp
, R
i=:
2kΩ, DC-free. Output is muted while reception. PTT :
max. 16V 0,2A to ground, input sensitivity: 200 mV
pp
to 10 V
pp
at 25 kΩ, DC-free. (can be modified to in-
crease sensitivity by factor 10)
Modem circuit: Texas-Instruments modem TCM3105. All frequencies are derived from a 4.433 MHz xtal.
Modem interface (digital): CMOS -level 5 volt. TXData, TXClock, RXData, RXClock, RTS CTS, DCD, + 5
volt, reset, ground. Connector: 20 pin (2x10) ribbon connector. Fits to TNC3, TNC31, TNC4 etc.
LED display: DCD (carrier detect), PTT (transmitter keying)
Jumpers and trimmers: Setting of output voltage with a 20 turn trimmer. Internal trimmers for DCD center
and trigger level. Solder jumpers for DCD source and watchdog disable.
Data Carrier Detect (DCD): Separate tone detector circuit (XR2211)
Watchdog: The PTT-switch is time-limited to approx. 40 seconds. In case of failure of the TNC, the PTT is
released after the maximum time. For tests or special applications (digipeaters with long transmission peri-
ods) the watchdog may be disabled by a solder jumper.
Measure Pins on board: DCD-PLL adjust and demodulator trigger level adjust.
Short description
A 'modem' contains modulator and demodulator circuits.
The FSK1201 converts the digital signals of a packet-radio-controller to low-frequent tones, which can be
transmitted by a FM radio. Further, it decodes the tones received by a FM radio and sends them to the
packet radio controller in digital form.
The modem AFSK1201 generates and receives audio frequency signals according the Bell 202 specifica-
tions, which is usual with amateur radio links (tone frequencies 1200 and 2200 Hz). All frequencies are
quartz controlled, adjustments are not necessary. The audio bandwidth of the signal goes from 300 Hz to
2500 Hz.
The transmit clock frequency (1200 Hz) is generated in the modem. The modem includes also the circuitry
for transmitter-keying (PTT) and transmit-time limiter (watchdog).
Bit-rate and baudrate
In this manual, the expressions bit-rate (bit/s, bit per second) and baud (Bd) are used for determining the
transmission speed. With the FSK1201 both values are equivalent, as there is exactly 1 bit transmitted with
every clock cycle. In general, it is possible to transmit more than 1 bit per clock, the speed (in bit/s) is then a
multiple of the clock rate.
Copyright for Hard and Software
All copyrights for schematics and board-layout belong to SYMEK GmbH or Ulf Kumm, Stuttgart.
The modem cannot be operated independently. So, it is a complex component and there is no need for a
EMI certification (CE-sign). When the modem is to be used in systems other than TNC3 or TNC31, the EMI
regulations have to be observed.
The contents of this manual may be copied as long as the author and the source is mentioned.