******************* FILE 4 of 6 FILES ********************** (C) 31 JUL 88 Eric Gustafson, N7CL 2018 S. Avenida Planeta Tucson, AZ 85710 DPLL Derived Data Carrier Detect (DCD) For Filter Based and Single Chip Modems COMMERCIAL TNC SIGNAL LOCATIONS (continued) AEA PK-232 The PK-232 is also relatively easy to interface in spite of the fact that AEA failed to implement a standard modem disconnect header even in their flagship TNC. For some reason, on this box AEA decided rather than bring out the wrong clock out to the external modem connector, they would bring out no clock at all. The Receive Data signal is obtained from the center pin of JP4. The Carrier Detect signal is obtained from the end of JP6 which is NOT connected to pin 3 of the external modem connector. The X32 baud clock signal is obtained from pin 13 of U8 (also a 74LS393 divider). The DCD output from the new circuit is inserted at the center pin of JP6. Use the NEGATIVE TRUE output. The jumper originally installed at JP6 is removed. To use the new DCD circuit with a PK-232 on VHF FM 1200 baud: 1. Set the audio level from the radio so that the tuning indicator "spreads" fully even on the station with the lowest transmitted audio level on the channel. 2. The existing DCD threshold control should be set so that the existing DCD indicator LED on the front panel lights up whenever there is ANY signal or noise input to the TNC from the radio. Be sure that even the station with the lowest amount of audio on the channel lights this LED. This LED should extinguish when there is no audio input from the radio (dead carrier from repeater etc.). If you wish to observe the action of the DCD signal generated by the new circuit, attach a 1 K resistor in series with a LED to the LED output of the new DCD circuit. The anode of the LED should be connected via the resistor to +5 volts. The cathode of the LED should be connected to the LED output of the new DCD circuit. If you wish, this LED can be mounted on the front panel where it is visible. Use a high effeciency LED. Pac-Comm TINY-2 The Pac-Comm TINY-2 does include a modem disconnect header. It is labeled J5 on their schematic diagram. For this they get +1 attaboy. Unfortunately, Pac-Comm attached J5 pins 11 and 12 to the wrong part of the baud clock divider chain. These header pins should have been in series with pin 1 of U10. This error results in there being a X1 baud clock signal on these pins instead of the X16 baud clock that should be there. So, even though they did implement a modem disconnect header, you will have to obtain the X16 baud clock from elsewhere on the circuit board. For this they get -1 attaboy (at least they are breaking even). The X16 baud clock signal is obtained from U10 pin 1. Receive Data is obtained from J5 pin 17. Negative true Carrier Detect (CDT) is obtained from J5 pin 2. NOTE! This is an inverted version of the CD output from the TCM3105 chip itself. Since this is a negative true logic signal, JMP1 on the new DCD circuit will be used instead of JMP2 which would normally be used for a TCM3105. NEGATIVE TRUE DCD from the new circuit is applied to the TNC at J5 pin 1. Remove the connection between J5 pins 2 and 1. The existing DCD indicator LED will NOT show the action of the new circuit. If you wish to observe the action of the DCD signal generated by the new circuit, attach a 1 K resistor in series with a LED to the LED output of the new DCD circuit. The anode of the LED should be connected via the resistor to +5 volts. The cathode of the LED should be connected to the LED output of the new DCD circuit. If you wish, this LED can be mounted on the front panel where it is visible. Use a high effeciency LED and increase the value of the series resistor to match brightness with the other front panel indicators.. If you wish to observe the action of the DCD signal generated by the new circuit on the built in front panel LED, you will have to do the interface a bit differently. First, you will get the negative true CDT signal from pin 1 of JPD. Then insert the LED output signal from the new circuit at either pin 2 of JPD or pin 2 of J5. Remove the jumper currently installed at JPD on the TINY-2 circuit board. If the new circuit is interfaced in this manner, the "RFDCD" signal can no longer be used. This is no great loss, however, as it will also no longer be necessary. (continued in file #5) EOF