[Xastir] A good time for APRS at 9600?

Bill Vodall wa7nwp at gmail.com
Sat Nov 12 23:30:58 EST 2011

> In the Pacific Northwest, there are a number of people experimenting
> with 9600 baud APRS. They have a reasonable network of i-gates and
> digipeaters. They've shown a couple of things: 9600 baud works for
> APRS; it can be more reliable for mobiles (less chance flutter will
> corrupt the packet, because the data burst is so short); and it ends
> up doing more for the network than halving the bandwidth because it
> moves a lot of stations off 144.39 and onto an alternate channel. Most
> of that network is Kenwood D700's, D710's, D7's and D72's.

Following up on Tom's comment above...    I've been almost exclusively
on the PNW UHF 9k6 APRS network for years and years.   In general --
it's great to get off the chaos of 144.39 and the system is working
better than every with multiple I-Gates and digipeaters.

Messaging just work's as long as you have a real I-Gate or two.   What
doesn't work is Voice Alert.   We've worked around that by bringing a
significant portion of the local 144.39 traffic to the UHF network.
Also I sometimes run with my second VFO on the Tone Squelched 144.39
channel just to see if anybody is in range.

It's really nice to have the extra bandwidth for more information...
We have DX spots of 6 meter openings, satellites, winlink2K access
points and the echolink/irlp nodes in the area and room for more.

As to TXdelay - ideally it would be a bigger win but since the D700 is
fixed at 1/2 second (silly Kenwood) it is far from optimum.  With the
light traffic load it's apparently a non-issue.

While 9600 is cool and it's trivial to set up with the Kenwood mobiles
PM feature, I recommend to anybody that asks to not use 9600 buad.
Two reasons:

1.  The data you can see on a mobile radio is the rate limiter.  With
a full 1200 baud channel the display too busy and distracting.
Anything beyond that from a faster 9600 channel is just unusable.
9600 would work good for a backbone but not a 'user channel.'

2.  If the goal is to help spread the load from the busy 144.39, you
don't want 9600 - you want 1200 which all the trackers use.  Moving
the dumb trackers off the main channel onto an alternate frequency is
good for both the trackers and the main channel.  Since the trackers
aren't running Voice Alert, they're the ones that can run there
without missing this incredibly useful APRS feature.

The big win is the alternate channel to spread the load which only
takes an I-gate or two to make happen.   Add digi's as necessary...

Bill - WA7NWP

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