Six Meter APRS Network

Bob Bruninga, WB4APR

The Northern VA and Baltimore areas have made substantial progress on the 6 Meter APRS network. The NoVa digi is NV4FM-6. Recognizing hams like to experiment and make use of readily available and innexpensive radios, this 6 meter APRS project has a few underlying objectives. This web page is to focus discusion on what those objectives might be.

  • Make use of high power surplus low band VHF radios
  • Use Innexpensive APRS devices that can fit inside the radios
  • Make the radios a black-box one freq-mobile
  • Interconnect to the APRS system via IGates (not to 144.39)
  • Use the radio receiver for Voice Alert with TONE 100
  • Provide for area-wide voice alert with a UHF crossband calling channel as shown above

    Discussion: The plot above shows what two digipeaters at about 100 feet above average terrain can do on 6 meters. This reminds me of the old wild-west days in the early 90's when the APRS network first began on 2 meters. Back then we could get From New ENgland to Georgia in 7 hops on RF because the digipeaters were high, and there were few users for collisions. Anyway, here are my thoughts on the potential use of 6m for APRS.

    Trackers: First of all, I am proposing this as primarily a tracking frequency. As everyone knows, I strongly object to the reference to the National APRS network as a tracking frequency, since it is designed to be an information distribution channel to the mobiles as much as positions-from them. But in this case, I think the availability of lots of 6m radios (many without control heads) makes this an ideal application for a trunk-mount black-box "tracker" system. THough everyone should consider a 2-way tracker where possible.

    PATHS: Since there has not been any formal network plan for integrating the 6m network with the national network on 144.39, we do expect that the 6m network will use long haul, multi-hop paths with large N's such as 7-7. So we want to make sure that such packets that might get linked over onto the national channel do not arrive there with large N's. Therefore the recommended standard paths for the 6m network to be:

    General Mobile Path: 6MTR7-7
    State, or section nets: 6SS7-7 for given SS or SSS states or ARRL sections...

    Voice Alert: However, we should take advantage of the receiver and an external speaker on these radios to implement th equivalent of Voice-Alert. Meaning the radio will receive a Tone 100 Voice call, to alert the operator to someone nearby who wants to talk, and announces his 2m or UHF REPEATER MONITORING frequency.

    Cross-band Link: While installing the digipeaters for this system, it might be useful to add a UHF remote-base link so that anyone in the wide area of this digi can call the 6 meter mobiles from the advantaged height of the digi. Again, this will be a call only, with the caller announcing his listening frequency either on 2m or 440, since the 6m tracking vehicles will probably not have a mic for talk back in some cases.

    DATA Reception: Although I would love to see these mobiles purchase 2-way APRS type trackers such as the TT-4 or OT-2 or HamHud or other devices so that they can receive and display APRS data and can receive their APRS messages, this is probably a ways off. In this case, however, the TNC device must be able to operate open squelch with direct connection to the discriminator so that it can receive packets while simultaneously keeping the Receiver Speaker squelched until a Tone 100 is received.

    I am open to comments on whether the typical surplus low band radios and TNC's can do this.

    This is just a draft web page... comments welcome.

    de WB4APR@amsat.org, Bob

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