Australian
Amateur
Packet
Radio
Association
MFJ1270B TNC
| Models | Specifications | Interfacing | Technical |
In order to expand the choice and lower the cost of entry into packet radio, AAPRA has obtained a quantity of first-rate, secondhand TNCs manufactured by MFJ Enterprises and dubbed the MFJ1270B. They are fully tested, come complete with circuit diagrams and installation instructions and are being offered at a very attractive price. This page is especially for those wanting more information on the MFJs.
Models
There are two models of the MFJ1270B:
- Standard - 1200 bps only (Sold out!)
- Turbo - 300, 1200 and 2400 bps
Specifications
- CMOS Z80A CPU clocked at 2.4576 MHz (option of 4.9152 MHz)
- 32K CMOS Static RAM (27C256) plus battery backup circuitry
- 32K ROM containing AX.25 protocol packet firmware
- Z80SIO/0 provides one asynchronous RS-232 port and one synchronous modem port
- Modem demodulator uses XR2211 PLL for 300 and 1200 bps (calibration software included)
- Modem modulator uses XR2206 to generate phase coherent FSK for 300 and 1200 bps
- Modem uses 1200/2200 Hz tones for 1200 bps and 1600/1800 Hz tones for 300 bps
- Transmit watchdog timer is included with 30 second timeout
- AX.25 version 2.0 protocol supported
- Operating modes include Converse, Transparent and KISS
- Personal Message System (mailbox) is included in firmware
- Fully compatible with a wide variety of TNC2 firmware (ROSE, NET/ROM, TheNet, 6Pack, JKISS, etc.)
- Accepts TNC2 compatible external modems via the internal 20 pin header
- Requires 12 volts at 400-500 mA (nominal)
Interfacing
| DIN SOCKET (RADIO) | |
|---|---|
| Pin | Signal |
| 1 | Mic Audio |
| 2 | Earth |
| 3 | PTT |
| 4 | RX Audio |
| 5 | Squelch Input (Optional) |
| DIP switch settings at rear of TNC | |
|---|---|
| Switch | Function |
| 1 | 300 bps to RS232 port |
| 2 | 1200 bps to RS232 port |
| 3 | 2400 bps to RS232 port |
| 4 | 4800 bps to RS232 port |
| 5 | 9600 bps to RS232 port |
| 6 | 300 bps radio modem enabled |
| 7 | 1200 bps radio modem enabled |
| 8 | 2400 bps radio modem enabled |
| Note: Only one of the switches 1 to 5 must be on at any one time. Only one of the switches 6 to 8 must be on at any one time. Example: For 1200 bps packet with 9600 bps to computer port, switch 5 and 7 would be switched on. |
|
Technical Talk
Power12 Volts is required for power up (13.8v nominal). The centre pin of the 2.1 mm coaxial plug is positive and the outside sleeve is ground.
RS232
The TNC has the same RS-232 interface as a conventional voiceband telephone modem and requires a similar comms port connection cable (available from AAPRA).
Jumpers
JMP5 is a link for the internal battery - this product has JMP5 disconnected
JMP4 is a link to disable the watchdog timer - link out is normal
Output Levels
R76 is a 20 turn pot to set the output audio level to the radio - min level when fully counter clockwise
R38 is a pot to set the output level of the 2400 bps modem (top of cct board)
Receive Level
Input audio level from millivolts to a couple of volts is acceptable. No adjustment for input level is usually necessary.
Startup
At power on the unit will display the start up text. CTRL C is the command to initiate the cmd: prompt. Type DISP whilst in command mode to display the parameters. These can be easily changed, however this is usually performed by the packet program on start up.
Deviation
To test deviation, power up the TNC and connect it to the radio. At the cmd: prompt type CALIBRA and Enter. Then press the K key to hear the transmit tone and tap the spacebar until the higher of the two tones is heard. It will unkey after a short time so press the K key twice whenever this happens, or link JMP4 to disable the watchdog timer. Adjust pot R76 (20 turn pot) for the correct deviation from the transmitter. Press the K key once to return to receive mode and the Q key to quit the calibrate mode. Be sure to remove JMP4 so as to enable the timer again.
Mailbox
To access the internal mailbox, at the command prompt (cmd:) type SYSOP. This allows you to retrieve messages, kill messages, etc. The mailbox must be ON to allow access (PMS ON) and it must have a callsign set with the MYPCALL command.
Last update to this page: 22/2/00