1274 From : W3CSG @ WB4D.VA.USA.NA To : MFJMOD @ ALLUS Date : 900724/1806 MsgID : BF 2079@WB4D, 605@KJ6YT $2079_WB4D Subject : More TX audio from MFJ1270B/1274 Via : AA6QN!N6KZB!KB6GVT!WA6PEZ!G3KFN!N8GTC!WB8ICL!NC8Q!W8BI!N8LJX!KD8JR!N8ET!WB8LYF!N8FIS!WB8JUI!NO8M!WA8BXN!WB8LVP!KC8JN!KA3NVP!W3KDC!WB4D Need more TX audio to drive a commerical radio or inject past the limiter? The following mod will increase the stock output from a MFJ1270B or 1274 TNC from about 200mv with tone twist to about 500mv with no tone twist. Change R56 from 7.5K to 4.7K Jumper out cap C71 Remove cap C73 Install 1mfd caps at C34 and C35 (caps shown on board but missing) The above changes will make the TNC TX audio the same as the older MFJ1270 and TAPR TNC2 units. I am presently using this mod in order to drive Motorola and GE radios in my node stack. 73 Royce W3CSG @ WB4D.VA.USA.NA ****************************************************************************** 1274.1 Subject: MFJ-1274 crashing solution A few weeks ago I placed a bulletin on the boards regarding a problem with the MFJ-1274 crashing from time to time. I received lots of replies and suggestions. I tried them all, and all of them failed to correct the problem. The was one which touched upon power failure, so I decided to look into the power supply. At no time was there a power failure or drop in voltage, but I removed the small 12v, 500ma supply that comes with the MFJ, and replaced it with a battery. The TNC ran fine until the voltage dropped on the battry 14 hrs later. The result was the TNC reset itself, and just sat there not doing anything. At this point I replaced the power supply with my PK-232 supply rated at 1 amp, and the MFJ has been running 100% for the l;ast 4 days. It is possible that the TNC is drawing more current then it's suppose to but in any case the 1amp supply is not running hot at all. So keep this in mind if something similar happens to your 1274. The problem may not appear if your TNC is not on continiously as mine is. Thanks to all for all the suggestions. Kd2ej Winston.. cmd: ****************************************************************************** 1274.2 *** TNC 2 - MFJ 1270 - and some Clones *** Tone Calibration Procedure Have you ever wondered to yourself whether or not the Packet TNC you are using may or may not be generating correct mark and space tones in reference to the proper frequency? As the owner of 5 MFJ 1270/1274 TNCs, the above question came to mind. I am not equipped to make adjustments on these TNCs with the use of various testing devices, and turned to the MFJ Owners Manual for a possible remedy. They tell you in the Manual how to adjust the tones if you desire HF operation (300 Bps) using their 1270B, or 1274 Model, but when trying to find out how to check for proper calibration on the VHF/220 Mhz/UHF (1200 Baud) -- it's not there. The TNC 2 has a couple of GREAT features built in to its software. CALSET and CAL are in the list of Parms, but not explained in detail that would enable the average packeteer to do his own calibration. 1. 1200 Hz. - MARK TONE (Low tone ) 2. 2200 Hz. - SPACE TONE (High tone) 3. 1685 Hz. - CENTER TONE (Demodulator) On the CENTER FREQUENCY tone, it states in the TNC 2 Manual that 1700 Hz is ideal. Continued experimentation has shown that 1685 Hz is best. If you are experiencing alot of retries, and having a difficult time with connects, chances are that your TNC is not generating compatible Mark and Space tones. To calibrate the 1200 Baud tones on your TNC 2 or Clone. Follow these instructions: 1. Remove the cover of your TNC. Make sure the HF/VHF button is in the "VHF" position! 2. Get a screw driver small enough to adjust the trim pots R-76 through R-79 located toward the rear center of the TNC circuit board. 3. Boot up your computer, and enter Command Mode (CMD:) on your TNC. 4. Try to listen on another Transciever, possibly a Hand Held Radio or monitor of some kind, and pick a clean freq. (simplex) with LOW pwr. This is helpful, but not required. CONTINUED IN 1274.3 ****************************************************************************** 1274.3 5. Enter this command from command mode: CALSET 438 or (n=525,000 / 1200 + 1) which in either case will equate to 438 or therabouts. This is your MARK tone CALSET number or 1200 Hz tone. 6. Remove the jumper from JMP 8 and place on JMP 9 Pins 1 and 6. (If you are facing your TNC pins 1 and 6 are on the far right). 7. Type CALIBRA or CAL. Hit the letter "K" and then the space key to get the lower of the two tones. NOTE: you may want to remove the jumper from JMP 5 to use on JMP4 to override the watchdog timer circuit. 8. Adjust R-78 until the you hear a change in pitch of the transmitted tone, AND both the CON and STA led's light up and stay lit, or at least alternate back and forth the same rate. Ideally, they should both stay lit simultaneously. 9. Hit the "K" again, and then "Q" (to quit calibration) and then go back to CMD: mode. 10. Give the TNC the command: CALSET 239 or (n= 525,000 / 2200 + 1) which equals a CALSET number of 239. 11. Repeat step 7. Repeat step 8, but adjust R-77. Repeat step 9. 12. NEXT - REMOVE the jumper from JMP 9 (Pins 1 and 6) and place the jumper on Pins 2 and 5. - the center two pins of JMP9. 13. Go to CMD: mode and type this: "CALSET 157" or (n= 262,500 / 1685 + 1) which would equate to a CALSET number of 157. This is your Demodulator/or center freq of 1685 Hz. 14. Repeat step 7, this time adjusting R-79 for the best condition of the CON and STA LEDs (both lit at same time). 15. Replace JMP 8 (from JMP9) and replace JMP 5 (from JMP4). Once you have done all of the above, you have successfully calibrated the TNC's tones. LAST BUT NOT LEAST...follow the MFJ or TNC 2 Manual on how to properly set the deviation level adjustment (R-76) so that your transmitter puts out in the neighborhood of 2.8 to 3.0 kHz of deviation. ****************************************************************************