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[aprssig] GPS/Puck or Other Wise

Stephen H. Smith wa8lmf2 at aol.com
Sat Jul 9 21:14:34 UTC 2005

rgilson at adelphia.net wrote:

> Any one got any suggestions for a WASS GPS which interfaces with a D7 
> or D700 and powers on with a signal from the Kenwood's.  Please no 
> Garmen Earthmate.  A display is not necessary but power on from the 
> Kenwood's is mandatory.  Power supply can be 12, 6, 5 VDC or 
> whatever.  I'm sure something has replaced RS Digitravelier.  Thanks.
> Ron 
1)   Earthmate is Delorme, not Garmin

2)   The Kenwoods don't provide any kind of explicit power-on control 
signals, especially the TH-D7 which has only a three-conductor bare 
minimum serial hookup (TXD, RXD, common through a 3-cond 2.5mm stereo 
minijack).   What they can do is provide a constant voltage on the 
outgoing data line from their dedicated GPS jacks indicating to an 
external device that the radio is turned on. . 

3)   The Garmin ForeTrex wrist devices will respond to (indeed require) 
the wakeup voltage on their incoming data lines before they start 
talking.  However this only turns off/on the RS232 interface in these 
devices (one of the most power-hungry subsystems); the main GPS RX and 
it's local LCD display remains live even when the RS232 is turned off.

A review of the ForeTrex is here on my website:

4)  Why worry about switching the GPS on and off at all?   A device like 
the Garmin GPS-18 powered by a decent switching mode regulator (not a 
7805 linear device) only draws 50-60 mA at 12VDC which translates to 
about 1 Amp-Hour a day.   You can leave this device on for a week or 
more without affecting the car battery significantly.  The advantage is 
that the  GPS is always locked  and has a currrent ephemeris and almanac 

Stephen H. Smith             wa8lmf (at) aol.com
Home Page:                   http://wa8lmf.com

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