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[aprssig] BLENDING APRS: SEEMLESS INTEGRATION IN A MULTI-FREQUENCY ENVIRONMENT

David Dobbins ddobbins at gmail.com
Sun Apr 18 00:37:36 UTC 2010


 Hi all APRS and NWAPRS enthusiasts:

Within the NWAPRS region a couple groups of hams have been developing
alternate APRS networks on 9600bd with great success. The project started
because the saturation of APRS activity on the primary freq, 144.39 at
1200bd, particularly around the Puget Sound region and Seattle. If you'd
tune into the 144.39 freq you'll rarely hear a quiet moment, and we suspect
upwards of 50% of the packet activity never gets through due to collisions
of u/i packets. I suppose this is happening in other larger metro areas
around the country and with our overseas friends.

The desire for further optimization sparked experimentation of 9600bd APRS
on both UHF and VHF frequencies. Success was found on both bands, but one
draw back on UHF was locating a common freq that could be expanded out of
the Puget Sound region. We still haven't discovered that common freq that
will work everywhere as we have on VHF, but we continue experimenting on
440.800Mhz under the direction of Bob (K7OFT) in Seattle. A typical WIDEn-N
digi on 9600bd employs a Kenwood TM-D700 in some locations, or an Icom
IC-207 and Kantronics KPC-9612 in others. Bob continues APRS development
on 220Mhz around the Seattle area as well. Bob (K7OFT) has proven APRS at
9600bd is a viable alternative to the crowded 1200bd activity on 144.39Mhz,
but also notes that while the D700 can DIGIPEAT in APRS Packet mode, it does
so with a limited set of commands. The D700 internal TNC is not fully
compatible with what we want to do within the compatibility
requirements. The D700 is just about the only rig we can use if we stay on
144.350 and 144.390MHz. The reason is because the D700 turns off the
receiver opposite of the band you are transmitting on. So if you transmit on
144.350 then the receiver on 144.390MHz is shut off, and
vice-versa. Otherwise the front end of the listening receiver could suffer
damage because the 40Khz may be too close to not cause problems. In Bob's
experimentation, we believe that the only way we can get around the limited
commands problem is to use Digi_ned at the digi site. Bob (K7OFT) also notes
we should be looking for an easy solution to passing messages and one-liners
to and from the primary and alternate frequencies.


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