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[time-freq] Assembled GPS timing kits?

John Koster w9ddd at tapr.org
Thu Jul 12 21:36:14 UTC 2007

You may have the 18PC confused with the USB version.  The 18PC has the 9 
pin serial connector and a voltage regulator built into the cirgarette 

The USB version will not become a serial unit by cutting off the plug.  
The manual isn't clear about it, but it implies that the USB doesn't talk
NMEA like the PC and LVC version do.  It certainly isn't going to talk 
4800 baud. 

Only the LVC versions have the PPS signal, so that's probably the one you 
need.  The tech manual does show how to connect it to the RS 232 port.  
You could steal the +5VDC from the USB, replace the 'battery' in their 
diagram with a USB connector.  The diagram doesn't show where to connect 
the PPS signal (yellow wire), you'd have to check the NTP docs to see 
where that should go.

The complete manual is available at garmin.com.  They keep moving things 
around, so it might be easier to fetch from:


However, that might not be the very latest version of the manual.  

On Thu, 12 Jul 2007, Pete Stephenson wrote:

> On 7/12/07, michael taylor <mctylr at gmail.com> wrote:
> > On 7/11/07, Pete Stephenson <pete at heypete.com> wrote:
> > > Instead, I'm wondering if anyone here happens to have any assembled
> > > kits (the exact GPS receiver is not important, so long as it's
> > > accurate enough to provide highly accurate time, as the kit will be
> > > connected to a computer to provide time to the local network and
> > > offered to the public NTP pool) that they'd be willing to sell.
> >
> > I guess I would consider simply an OEM GPS module connected direct to
> > the computer running NTP, like the Holux GR-213, which I think you can
> > pick up for about $50-75, Garmin GPS 18 PC, or the Trimble's
> > Resolution T (~$100 US) which is the cheapest "timing" GPS module I
> > know of.
> Michael,
> That would be ideal. I was leery of GPS products sold at local retail
> establishments, as I suspected they wouldn't be all that great for
> timing, just like how most handheld navigational GPS units aren't
> great for timing.
> It looks like the Garmin GPS 18 PC is exactly the same as the GPS 18
> LVC, except that the PC has a USB plug on the end, while the LVC has
> bare wires. Correct me if I'm wrong, but wouldn't it be pretty easy to
> just snip off the plug and re-wire it as a DB9 serial plug, but still
> have it draw 5v power from USB?

John, W9DDD

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