[aprssig] 9600 APRS net experiment in Central NJ

Herb Gerhardt hgerhardt at wavecable.com
Fri Feb 25 23:47:59 EST 2011

Here in the Pacific NW we are experimenting with 9600 baud on both 440.80
and also on 144.35.  I am using 144.35 at 9600 baud and in my area it works
better for my trackers than the standard 144.39 at 1200 baud.

We use either a D700 or a D710 for our digipeaters and do not use a computer
for digipeating since that is not good policy for our high mountain top
digipeaters which are not accessible do to snow for a good part of the year.
I have such a duel digi set up on South Mountain in Western WA at the 3000
ft level.  There the left side of the radio is set to 144.350 using the
built in TNC at 9600 baud set to packet TNC mode and the right side of the
radio is set to 144.390 using an external KPC3+ TNC at 1200 baud.  This
system uses only one antenna for both sided and can only transmit on one
side at a time.  People have also told us it was not possible to do this
since the frequencies were so close together but all we can tell it you it
seems to work just fine.  Sure there will be some packets that are lost
because the radio can only transmit on one frequency at a time but that does
not seem to cause any noticeable affect......

The only drawback for doing this on a mountain top that is not readily
accessible, is that you cannot remotely control the internal TNC but you can
still control the KPC3+ remotely as usual.  I had the internal TNC reset
itself for some unknown reason when I first installed this set up but the
external TNC kept right on ticking, so I only lost the 144.35 side until I
was able to get back up there and get things squared away again.  Added some
shielding over the control head and a magnetic torride to the control head
cable and it has operated that way for over 6 months now without any

So this is a fairly simple way to set up a duel 9600 baud and 1200 baud
digi.  The only thing is you have to sacrifice a D700 or D710 radio.  Not
sure if you could use a D7A(G) or D72A since the external TNC in the above
set up is connected through the 6 pin data port on the radio.

We have a number of similar mountain top digipeaters set up like this and
are even doing some fancy computer stuff with a mountain top internet feeds
to a home computer and are blending to two systems so that what one hears it
is also transmitted out on RF on the other side.  On our 440.800 network, we
also do similar blending between it and the 144.39 system.  We can send RF
APRS messages between all three system.  Pretty slick stuff...  No, I am not
the one who came up with these ideas but once I saw it in operation, I was
willing to try it and liked it.....

Herb, KB7UVC
NW APRS Group, West Sound Coordinator
Our WEB Site:  http://www.nwaprs.info 

> -----Original Message-----
> From: aprssig-bounces at tapr.org [mailto:aprssig-bounces at tapr.org] On Behalf
> Wayne Sanderson
> Sent: Friday, February 25, 2011 3:18 PM
> To: aprssig at tapr.org
> Subject: Re: [aprssig] 9600 APRS net experiment in Central NJ
> >I have a spare PC, a spare 2 Meter HT with standard speaker and mic
> >jacks, a small cigarette packet sized TNC that will do KISS and AX25,
> >a spare D700 and a D7AG that is now a backup since I got my D72 the
> >other day (Yowiee!- I love the thing!) I propose to do the following:
> >1- Connect the pocket TNC to the spare HT and use it to connect to the
> >main APRS channel. I expect that the radio will be low powered enough
> >on TX and deaf enough on receive with a rubber duck antenna that it
> >will hit and hear only the closest digi.
> Now that I am looking at the thing, I realize I can connect the
> TNC leads to the TH-D7A(G) through those jacks and forget the spare HT.
> Anyone run digital on both sides of a Kenwood this way? (Radio hooked
> to PC in packet mode, Internal TNC on one band at 9600, external TNC
> through jacks on the other band at 1200)

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