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

John Langner WB2OSZ wb2osz at comcast.net
Wed Jan 25 11:40:07 EST 2017

> 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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