[ntp:questions] Re: Good GPS for attic?

Richard B. Gilbert rgilbert88 at comcast.net
Fri Feb 11 22:17:31 UTC 2005

Jonathan Sturges wrote:

> Hi,
> I'm looking to use a GPS receiver as an inexpensive reference clock 
> for an xntpd time server.  I'd like to leave the GPS in my attic for 
> convenience and asthetics.
> A while back I bought a Radio Shack DigiTraveller GPS for this 
> purpose.  It's ideal on almost all counts except that it can't keep a 
> consistent lock from my attic.  It's close though (maybe if I could 
> mount it above the insulation that would help).
> Can anyone recommend another inexpensive GPS that might be more 
> sensitive?  I don't want fancy, just plain-jane with a serial port 
> that can spit out NMEA strings for xntpd.  PPS would also be nice, but 
> I'd be happy without it too.  (I'm mostly doing this to have a time 
> reference for household computers, and also just the experience of 
> setting this up.  Fantastic precision would be nice but certainly not 
> required for this particular project.)
> thanks,
> Jonathan

Any indoor antenna may provide spotty reception or no reception!  A new 
receiver may or may not help.  A better antenna placement should 
definitely help.  Remember that, if you put your eye where you plan to 
put the antenna, and you can't see the sky from horizon to horizon you 
will probably have problems from time to time.  The bottom ten degrees, 
or so, all the way around are less important than the rest but get those 
too if you can.  Even dense foliage can weaken or block the signals!

You can purchase a Motorola M12+ Timing Receiver Evaluation Board from
Synergy Systems LLC <http://www.synergy-gps.com/>
for around $200 US.  It has PPS output and is rated to hold the PPS 
within 50 nanoseconds.   The evaluation board is just that, a bare 
circuit board with components installed.  It comes with a "hockey puck" 
antenna and a power supply.  Receivers are also available installed in a 
case but they cost more.

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