[aprssig] Sharing GPS

Michael Barnes barnmichael at gmail.com
Wed Dec 27 01:10:50 EST 2017

Thanks to all who responded. Most of the replies apparently came directly
to me only, not to the list. For those who didn't see them and are
interested, the most favorable replies were regarding the use of gpsd to
process the NMEA data from the GPS receiver and use gpspipe to direct it to
the other equipment via a USB-serial port and adapter. I had used gpsd in
the past, but forgot about it until reminded.

In previous projects I have simply connected up to four RxD lines in
parallel and fed four computers from a single GPS receiver. However, in
that case, the receiver had its own fixed supply and an RS-232 output. The
RxD was fed to multiple computers and the TxD from only one computer went
back to the receiver for configuration purposes. In my case, the GPS
receiver is a USB device, receiving its power and bi-directional
communications from the RPi USB port. Utilizing gpsd and gpspipe, I will
output the data to a USB port and that will connect just the TxD pair
through a USB-to-serial adapter. The output from the adapter will be
paralleled to the RxD inputs on the Icom and Uniden radios.

For those who asked, the Icom IC-7100 has D-Star and apparently uses GPS
location data to provide tracking via D-Star repeaters. It also can locate
nearby repeaters which are linked to the D-Star system. I don't know
anything else about it, yet, but expect to play with it some when I get it
all set up. Regarding the Uniden scanner, the BCT-15X has a neat feature
that allows me to geotag groups of channels for automatic activation. So,
as I travel through counties X, Y, and Z, the appropriate channel groups
will be activated for the location I am actually in. When in County X,
Channel Group X will be active, when I move into County Y, Channel Group X
locks out and Channel Group Y unlocks. Sounds interesting in theory. We'll
see how it does in practice.

Again, thanks to all for your comments.

Michael WA7SKG

On Tue, Dec 26, 2017 at 7:09 PM, Nick VA3NNW <tapr at noseynick.com> wrote:

> Jason KG4WSV wrote:
> > Brett Friermood wrote:
> >> Gpspipe can be used to pipe NMEA data from gpsd out a select serial port
> > cool, i'll be trying that one out. Sounds like it'll work for Michael,
> too.
> NMEA, unless I'm mistaken, is entirely TXD from the GPS to RXD at the
> computer. The computer end ought to be high impedance on that pin, so
> you ought to be able to make up a special-purpose cable connecting just
> GND to GND, and GPS NMEA TXD to computer RXD, and probably to 2, 3, or
> more computers' RXDs.
> What would NOT work would be any kind of combining of multiple
> computers' TXDs into GPS RXD. but in this case you shouldn't need
> computer->GPS anyway.
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