19.2kb modem for TNC2 ?

Discussion in 'General Technical Questions and Answers' started by Guest, May 26, 2002.

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  1. Guest

    Guest Guest


    I'm looking for a 19.2kb modem for the TNC2. Anything like that out there?

    I understand about having to upgrade the CPU to higher clock speed, thats no problem.

    Charles N5PVL
  2. W9GB

    W9GB Ham Member QRZ Page

    The most common add-on board for the TNC2 was the 9600 baud modem (G3RUH design).



    From Barry McLarnon, VE3JF on the TAPR web site (circa 1996):

    Until recently, operation at 19.2 kbps had not received much attention. A major reason for this is that binary FSK at 19.2 kbps cannot be accommodated by the IF stages of NBFM receivers, nor is it compatible with the 20 or 25 kHz channel spacing used for FM in the amateur VHF/UHF bands. On the other hand, it makes relatively poor use of the 100 kHz channels typically allocated for 'wideband' digital modes. However, interest in 19.2 kbps operation was spurred by the appearance of the Kantronics D4-10 radio. Since it contains a varactor modulator, plus a data slicer following the discriminator, it can be operated in 'raw FSK' mode at 19.2 kbps without additional modem hardware. All that is needed in addition to the radio is the computer interface. A 'souped-up' TNC might work fairly well, but one of the PC DMA interface boards (or maybe a DataEngine) would be better. Running 'modemless' FSK entails some loss of performance, most notably from the lack of data scrambling, which results in more jitter in the recovered clock signal and thus higher bit error rates.

    Kantronics also offers a 19.2 kbps modem, similar to the DE9600. The performance difference between the 'barebones' D4-10 radios and that which you could realize with the more sophisticated modem has not, to my knowledge, been quantified. The GRAPES modem (see below) could also be run at 19.2 kbps, but it would not be compatible with the Kantronics equipment (and why would you want to throttle back a modem that can do 56 kbps and more, to only 19.2?).

    Some experiences with using the D4-10's at 19.2 kbps, using Ottawa PI cards and DataEngines as interfaces, appear in an article by John Ackermann, AG9V in the 11th ARRL Computer Networking Conference Proceedings (available from TAPR). Unfortunately, Kantronics discontinued the D4-10 in 1995.

    PacComm did offer 2W and 5W Tekk radios which have been modified for 19.2 kbps operation:

    Tekk KS-900L-D192 2W data transceiver with 19.2 kbps filter mods ($199)

    Tekk KS-1000L-D192 5W data transceiver with 19.2 kbps filter mods ($209)

    The filter upgrade kits are also sold separately ($39).
    The Ottawa (Canada) PI2 (Packet Interafce 2) card kits are no longer available and they have no plans to make more.

    You might inquire with Symek (Germany)


    They have an FSK9601 product with a 20 pin header (found on many commercial TNCs), but you should inquire regarding compatibility of interfacing with your specific TNC. Symek also has a series of add-on boards that they developed for the UoSAT-12 satellite project.

    Digital Modes web site

  3. Guest

    Guest Guest

    Sure do appreciate the info. It looks like I may have to try something different.

    I wonder how a 9.6kb fullduplex link would compare to 19.2 half-duplex?

    Charles, N5PVL
  4. VE6BUD

    VE6BUD Ham Member QRZ Page

    Well, 9600 bps is pretty fast as it is. Sure beats the pants off of 1200 bps for regular text browsing.

    What I don't understand is, why does raw FSK have to be used when it's already been proven that PSK (Phase Shift Keying) can already be used on HF?

    Someone just needs to think it up and deploy it.
  5. W9GB

    W9GB Ham Member QRZ Page

  6. Guest

    Guest Guest

    No doubt! The new BayCom USB modem looks excellent, price is right too.

    For my part, I am more excited about the PCI bus HDLC card they make, that takes up to four plug-in modems.

    After looking at all the available equipment, the BayCom stuff appears to be heads and shoulders above the rest.

    I'm not interested in modifying the TNC2 for 19.2 any more. I guess the thread is dead.

    Charles, N5PVL
  7. W9GB

    W9GB Ham Member QRZ Page

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