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[aprssig] [nwaprssig] THOUGHTS ON RELIEVING APRS CONGESTION ON 144.39

David Dobbins ddobbins at gmail.com
Wed Nov 17 23:22:07 UTC 2010


If it snows in hell, no variety of APRS is gonna save us. Not 1200 baud, not
9600 baud. It's inevitable we are doomed for destruction. Nonetheless, I'd
still like to see the issue resolved and all our efforts go to working
together to get it done.

Thanks for the input, Bob.

Dave K7GPS

On Wed, Nov 17, 2010 at 10:51 AM, Robert King <krm1012 at live.com> wrote:

>  Using the D700/D710 for operating from a commercial repeater site is a
> poor solution to the 144.390Mhz APRS congestion problem.  The technical
> problems do not go away by simply "dismissing" them.
>
> While using the D700/D710 may be the cheapest alternative to the
> congestion, It has it's problems.
>
> 1.  There is NO control of packets going from frequency to frequency.  We
> are back to the old problem of  different baud rates on the different
> frequencies. This is similar to the 300 Baud / 1200 Baud HF/VHF  problem
> with no control of congestion on the lower Baud frequency..
>
> 2  It is true that while one transmitter is transmitting on 144.350MHz the
> corresponding receiver is turned off on 144.390MHz and vice versa so there
> is no desensing or damage to  that receiver, it remains that the 144.390Mhz
> receiver is DEAF during the time the 144.350MHz  transmitter is on.  This is
> reciprocal.  It is a self defeating feature. If one frequency is very busy
> (144.390) then 144.350 is blocked out completely. The best one may say about
> this solution is that it works  --  part time.
>
> A much more elegant and expensive solution is to use two transceivers on
> widely separated frequencies using the same antenna with a duplexer to
> eliminate the desensing. And a smart program to gate from one frequency to
> the other so that control of the flow of packets can be implemented.
>
> Yes, it is a more expensive solution.  But it will work smoothly with no
> packet getting dropped because of blocking by a deaf receiver.  Messages can
> be handled properly from one frequency to another.
>
> We need to think carefully about the scheme we use before we commit to a
> solution for congestion.  The cheapest may not be the wisest way to go.
>
> If someone has a better solution we need to hear about it.
>
> To me, the best solution is the simplest.  Everyone should convert to 9600
> baud on 144.390 MHz.  There would be an immediate tripling of throughput.
> But for this to happen there would have to be a snow storm in hell.
>
> Bob King
> K7OFT
> krm1012 at live.com
>
>
>
>
>
>
>
>  From: ddobbins at gmail.com
> To: aprssig at tapr.org; nwaprssig at nwaprs.info
> Subject: [nwaprssig] THOUGHTS ON RELIEVING APRS CONGESTION ON 144.39
> Date: Tue, 16 Nov 2010 19:28:45 -0800
>
>
>
> Hello fellow APRS enthusiasts. I’m curious to know what the rest of the
> world is doing to relieve some of the congestion of APRS traffic on the
> primary freq 144.39? In my wide travels, my experience has been the larger
> metro areas are suffering from APRS indigestion, meaning if you turn the
> volume up on 144.39 and listen, it’s uncommon to hear any break in the
> packets the closer you get to the big cities.
>
>
>
> I’d like to share what we’ve been doing about this oversaturation of the
> primary freq in the Puget Sound area. For the past couple years we’ve been
> experimenting with, and done some implementing of APRS at 9600bd on both UHF
> and VHF. The initial alternative frequency/speed experimentation began on
> UHF 440.800MHz at 9600bd by Bob King, K7OFT. We have several UHF APRS
> digipeaters around the Seattle area. The typical digi setup is an Icom
> IC-207 and Kantronics KPC-9612, using the same configuration settings found
> on the primary frequency. The biggest group of users are mobiles, typically
> those with TM-D700/D710 or the Yaesu FTM-350R and similar handhelds. Those
> tracking on the UHF frequency are gated to the APRS-IS, and those with an
> internet connection at their home station will see both the VHF primary, and
> UHF secondary APRS activity. Our VHF 9600bd effort commenced a little later
> than the UHF interest, but has grown significantly over the past year, with
> several high level digipeaters serving the alternate VHF frequency
> 144.35MHz. Scott Cronk, N7FSP has been leading this effort. We eliminated
> the possibility of interference between the two freqs (144.39 and 144.35) by
> replacing an existing APRS digipeater VHF radio with a Kenwood TM-D700 or
> D710, and retaining the existing KPC-3 (or an Argent TNC). The internal
> radio TNC operates at 9600bd on 144.35, and the other side of the radio is
> set to 144.39 and uses the external 1200bd TNC. No change to the filter
> solution has been necessary, or need to add or change antennas, since the
> two freqs are close together. We’ve had three arguments presented why this
> solution wouldn’t work, and all three have been dismissed. First, folks said
> 9600bd won’t work on VHF. It does, and quite well. Second, folks said the
> two freqs were too close together and would cause interference. Not so, as
> the D700 becomes “deaf” on one side of the radio when the other side is
> transmitting, thus no issue. Third, while one side was transmitting, there
> would be packets not digipeated on the other side. We’ve found this to be
> not much of an issue, and the increase in packet loss at the digipeater is
> insignificant. We have a growing number of mobile users throughout Puget
> Sound using the 144.35 APRS @ 9600bd with very good results. With several
> iGates, including direct IGating from the mountaintop digipeaters with
> internet access, everyone trying to get their data to the APRS-IS is getting
> through. We’re encouraging home and other fixed stations to make the switch
> to the alternative frequency to further relieve some of the congestion on
> the primary frequency. It’s too early to tell just how much relief we’ve
> seen on the primary frequency, and difficult to measure. We've also been
> experimenting with cross-banding of data, feeding packets and messages back
> and forth between the VHF 1200bd, VHF 9600bd, and UHF 9600bd channels.
>
>
>
> We’re also encouraging makers of the VHF trackers to add 9600bd capability
> to their products. For those folks in areas oversaturated by APRS packets, I
> suggest the next time you make the mountaintop digipeater run to replace the
> existing VHF radio with a Kenwood TM-D700/D710 and give dual-APRS ops at
> 1200bd and 9600bd a try.
>
>
> Dave K7GPS
>
> NWAPRS Spokane Area Coordinator
>
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