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[aprssig] COR and MIC-e repeater

Wes Johnston aprs at kd4rdb.com
Sat Feb 19 03:16:59 UTC 2005

Having just installed a TNC at the repeater site, I discovered that our
controller  (RC-110) does not have a kerchunk filter.  I'd like to add one to
it, and using a 555 timer came to mind (you can fix anything with a 555 timer,
a basic stamp and some duct tape)... more on that later.

Can someone refresh my memory about a one shot?  I don't think it'll do exactly
what I'm looking for...  COR is low at rest, and active high.  I want to have
the timer fire after .25 seconds of COR HI, and if the receiver's COR drops for
upto .25 seconds, have it drop COR to the controller.

We have a TNC at the repeater is using it's MUTE line to hold COR low and mute
the packet.  Problem is, the TNC takes 10 to 12 mS to see the packet an mute it
by asserting COR.  But if the repeater was not already in use, and since it does
not have a kerchunk filter, even that 10mS of active COR is enough to cause the
repeater to come on air.

The point to all of this is that if I hook a tiny track up to a radio, it may
periodically send a packet when my vehicle is parked and the repeater is quiet.
 I'd like the repeater to stay OFF air if it's only a packet on the input.

Now, back to the duct tape story... on the way to repeater site today, it dawned
on us that we didn't have a 440 antenna on site to get the aprs positions out on
70cm to the local digi.  My partner in crime was at home and I asked him to
bring a mag mount antena.  He didn't have one, so I asked him to bring a coat
hanger and some dykes.  We did discover that the ATV 70cm antenna was not in
use and used it instead of the coat hanger.


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