PacComm NB96 MODS ~~~~~~~~~~~~~~~~~ by Mike Curtis WD6EHR ~~~~~~~~~~~~~~~~~~~~~ The PacComm NB96 G3RUH modem has a jumper-selectable "defeat", JPS. When a jumper is in position here, the modem disconnect is normalled through. I've installed a DPDT slide switch on the front of my MFJ 1274 to make radio baud rate changes simple. The first pole is used to make the connection to JPS.The second pole is used to change the radio baud rate selection normally made by the rear apron DIP switch. A quick and dirty DCD LED can be easily added to PacComm's NB96 9600 baud modem board. Pin 13 on U-10 supplies a DCD signal. Connect a 680 ohm resistor and LED between this and +5 volts, obtainable on pin 24 of S-1 or S-1a, both 26 pin connector positions on the PCB. Only one is used. Solder your +5 volt wire into the unused hole of the other. Tack the other lead to U-10 pin 13, or if you do the "garbage" mod below, to pins 8 and 9 of the 74HC00. You may also use the DCD LED in your TNC by lifting the cathode of the LED, inserting a diode in series, tacking a second diode to the LED cathode, and running the cathode of this to modem U-13 pin 10. 4.3.2.1 G3RUH "GARBAGE" MOD ~~~~~~~~~~~~~~~~~~~ by Steve King KD7RO ~~~~~~~~~~~~~~~~~~~ Gets rid of random garbage "calls" in MHeard (edited) Here is the modification I made to my PAC-COMM NB-9600 modem. This mod got rid of all the garbage calls in my mheard list both when using the TNC in standard mode as well as while using net/nos software packages. This modification makes sure that the modem will send all zeros to the TNC until the modems PLL is locked on a signal. This means that the TNC will not be reading garbage coming in to the UART all the time. 1. Remove socket for U11 (74HC14). 2. Insert the 74HC14 directly into the PC board. 3. Lift all the pins of a 74HC00 except 7, 12 and 14. 4. Bend pins so they are pointing straight out. 5. Cut back the bent pins so the 74HC00 can be piggybacked on the 74HC14. Without removing the socket on U11, I would not have ben able to slide the modem and Tiny-2 back into the box (you may not have this problem). 6. Cut the trace from U11 pin 12 to U20 (74HC157) pin 13. 7. Solder the 74HC00 on top of U11 (soldering pins 7, 12 and 14). 8. Wire U10 pin 13 (LM339) to the 74HC00 pins 9 and 10. 9. Wire 74HC00 pin 8 to pin 13. 10. Connect pin 11 of the 74HC00 to pin 1 and 2 of the 74HC00. 11. Connect pin 3 of the 74HC00 to pin 13 of U20 (74HC157). 12. Put a piece of tape over the top of the 74CH00 to insulate from the case. The DCD signal coming from U10 (LM389) is low true so I invert it using one of the nand gates (pins 8, 9 and 10). This is used to qualify the RXD signal from the 74HC14 (pin 12). Pin 11 of the 74HC00 is the RXD signal (low true) qualified by the DCD signal which is LOCK DETECT. One more inversion of this signal (74HC00 pins 1, 2 and 3) and I have the qualified RX DATA signal which is connected to U20 (74HC157) pin 13. RX DATA is always zero until the PLL is locked to the data. Then RX DATA will be the true data comming from the unscrambler or zeros if we are not locked. Steve King (KD7RO) king@hpdml57.boi.hp.com Hewlett Packard Boise, Idaho