******************* FILE 5 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) Kantronics KAM Interfacing anything to a Kantronics box isn't a job, it's an adventure! Kantronics has an official policy of discouraging anyone from hooking any third party device to their TNCs. This includes external modems of any kind (Never mind that their crystal ball has proven cloudy at best in the past when trying to predict what modems might be popular or necessary in the future). This policy was enunciated to me by persons in their technical support department in two separate telephone conversations. So it was not surprising to find that they didn't provide a modem disconnect header in the KAM. What I did find a little surprising, however, was the fact that they also refuse to provide an individual owner any assistance with signal locations. They don't say they don't know, they say they WON'T help you! If you want, for instance, to interface a JAS-1 (FO-12) style BPSK modem to your Kantronics TNC, you are on your own as far as Kantronics is concerned. Potential Kantronics buyers who are interested in working digital modes through this and the upcoming MICROSAT packet store and forward satellites should take note. If Kantronics thought that one day they might possibly make a radio, you would have to use the optional Kantronics built-in radio in all their TNCs. Thank goodness they don't also make computers... It turns out that the necessary signals ARE available (for 1200 baud at least) in the KAM. It is indeed possible to interface either the 1200 baud BPSK / MANCHESTER FM modem required for the JAS-1 bird or this DCD circuit (or both) to the KAM. At this time it is unclear whether the required clock signal is available for the DCD circuit to operate at 300 baud on this TNC. Even if it is, it would be more trouble than it is worth to interface as it would either require two separate DCD circuits or a switching arrangement to allow the use of one for both modems. Since it is unlikely that the filter / slicer modem used in this box is a stellar performer when working with small shift to baud rate ratio signals of the type used for HF packet, maybe we should only really concern ourselves with 1200 baud operation anyhow. It is worth noting that for wider shift to baud rate ratio signals like RTTY, ASCII, and AMTOR the filter / slicer type demodulator performance is perfectly adequate. When the shift to baud rate ratio is greater than 1, as with these modes, most of the transmitted signal energy is concentrated around and very close to the two tone frequencies. When this is the case, the filter / slicer is the preferred method of demodulation. As these modes do not operate in a Carrier Sense Multiple Access (CSMA) environment like packet requires, the built in CD function is adequate for these modes as well. For 1200 baud operation then, the signal location points of interest in the KAM are as follows: The Receive Data (RXD) signal is obtained from pin 8 of the TCM3105 modem chip. The Kantronics schematic shows what appear to be some numbered pads (17 and 18) on this lead to the processor. If you can locate these points on the circuit board, it may be easier to obtain the signal from one of these points. The X16 baud clock signal is obtained from pin 2 of the TCM3105. The POSITIVE TRUE Carrier Detect (CDT) signal from the modem is obtained from pin 3 of the TCM3105. This line from the modem to the CPU is labeled with 2 numbered pads (7 and 8). The connection between these 2 locations should be broken. JMP2 on the new DCD circuit will be used. The DCD output from the new circuit is injected at pin 21 of the 63B03 CPU. The front panel LED which normally indicates the CDT signal activity will show the action of the new DCD circuit. (continued in file #6) EOF