Hi,
Talking about "decent" multiplexers, all our NMEA multiplexers have
"automatic GPS back-up switching" (plus many other NMEA sentence
management
features). Read about it he
http://brookhouseonline.com/gps_backup_switching.htm . I have been
playing with the idea to add a buzzer to warn the user when it switches to
the backup GPS. As the "no GPS data" detection is already present, this
is
very simple to do. If there is sufficient interest, we'll include it as a
standard feature. If you want it NOW, we'll add a buzzer to the present
model for a small charge if you decide to buy one.
Wout

Ehh, talking about "Decent" multiplexers: decent multiplexers have isolated
inputs, yours don't.

I just connected one of yours to a differential NMEA talker output. I can
now hear all NMEA data on my SSB!!

While trying to find out what's wrong, I found that all inputs on your
multiplexer have the B terminals connected to ground!!! NMEA inputs are
supposed to be isolated. Your grounded B terminals on the inputs effectively
short-circuit any properly designed talker. Was it that hard to add 50 cents
worth of optocouplers?

Gert