[aprssig] bad paths and digipeaters?

Wes Johnston aprs at kd4rdb.com
Mon Nov 29 19:56:54 EST 2004

Here's an idea... if you use a kpc3 or similar type TNC as a digipeater, leave
MON ON, and hook a basic stamp to the serial port.  The TNC will copy each
packet to the serial port just before digipeating, right?  Have the basic stamp
read the packet, count the hops and if it determines that the count exceeds the
local custom, have it interrupt the PTT line to the radio.  It could pull a
relay in to interrupt whilst watching the PTT pin from the TNC to release.  It
would keep the relay pulled in until the TNC released PTT, the let the relay
drop.  This would have the effect of allowing an external processor to
interrupt the TNC's access to the radio.  Each basic stamp (or PIC, or ATMEL)
could be programmed to respond, err inhibit, based on a different number of
hops determined by the local sys op.

As an example, a user sending out WIDE7-7 in a path would be digipeated by the
kpc3 firmware.  But if this PTT interrupter saw WIDE7-3, and the digipeat hop
limit was set to 3, then it would interrupt the PTT when the tnc tried to
digipeat WIDE7-3.


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