[aprssig] 2 Port Digitpeater was: APRS UHF freq? (9600 baud)

Ev Tupis w2ev at yahoo.com
Thu Jan 26 06:22:50 EST 2017

My particular need is for a time-hardened installation at a location that is not easily accessible once installed.  I will be able to use DTMF to power-cycle if pressed, but 24/7/365/forever operation is the expectation.
Has such operation been demonstrated (no "memory leaks") with any computer-as-a-controller solution?

      From: Kenneth Finnegan <kennethfinnegan2007 at gmail.com>
 To: TAPR APRS Mailing List <aprssig at tapr.org> 
 Sent: Wednesday, January 25, 2017 4:59 PM
 Subject: Re: [aprssig] 2 Port Digitpeater was: APRS UHF freq? (9600 baud)
Agreed; we really shouldn't be setting up null-cable KISS crossbands for APRS these days. Between Direwolf for its own modem and Aprx for other KISS TNCs both having multi-port digi support, and single board computers / MicroITX industrial PCs being so cheap, you can set up very intelligent cross-band digi for not much more than the rest of the system expenses..
Kenneth Finnegan
On Wed, Jan 25, 2017 at 8:40 AM, John Langner WB2OSZ <wb2osz at comcast.net> wrote:

> Has anybody actually succeeded in putting two KISS TNC's "back to
> back" to form an independently operating (no computer between them)
> two-way "bridge" to pass traffic bi-directionally?
> Lots of suggesting that this could work, but has it been done?

In theory it should work but it's not a proper solution to the problem.
Here is why.

When a packet is first transmitted, the via path contains information on how
it might be forwarded by digipeaters.

Each time a digipeater retransmits a packet, it modifies the via path to
decrease the number of possible remaining digipeater hops.  This limits the
number of times it can be retransmitted.

If you were to simply retransmit what you hear on one frequency onto some
other frequency, that would be OK if only one person was doing it.  However,
if you had two stations like this, that could hear each other, the same
packet could go bouncing back and forth forever.

To do it properly you would want to put an application between the two TNCs
to perform digipeating by the normal rules.  There are countless digipeater
implementations out there but I'm not sure how many of them can handle
multiple radio channels at the same time.

The "direwolf" software TNC can handle up to 6 radios at the same time and
has the ability to digipeat between different channels in any combination.
Run it on a Raspberry Pi and you have something smaller and cheaper than a
stack of old TNCs, with better receive decoding, and vastly more

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