Cheap serial GPS

pmellen

Hi,

I would be interested in how to find these on eBay please?

whosmatt

@Nnyan:

Excuse my ignorance but what would you use these with pfsense for?

pfSense can use the time signal provided by the GPS as a reference s/cock/clock/ for NTP.

pfBasic

pfsense can use the time signal provided by the GPS as a reference cock for NTP.

This is significant, reference cocks are not easy to find. There are so many variations that it is really difficult to find a high quality, standardized cock to reference all of the other cocks to. Most cocks advertised as "reference cocks" actually jitter far too much to be usable.

kpa

@pfBasic:

pfsense can use the time signal provided by the GPS as a reference cock for NTP.

This is significant, reference cocks are not easy to find. There are so many variations that it is really difficult to find a high quality, standardized cock to reference all of the other cocks to. Most cocks advertised as "reference cocks" actually jitter far too much to be usable.

;D

ajm

@Nnyan:

Excuse my ignorance but what would you use these with pfsense for?

To run a Stratum 0 NTP service for all local IT systems. Benefits:

Zero external NTP traffic leakage, resulting in reduced opportunity for fingerprinting etc.
Reduced dependence on external services outside my direct control.

I run a local recursive nameserver for similar reasons.

HTH

doktornotor

@pfBasic:

reference cocks are not easy to find.

stephenw10

So no PPS output at the plug?

Steve

ajm

@stephenw10:

So no PPS output at the plug?

Steve

Only by opening the device and soldering a patch wire into the correct pin (#21) on the SIRF module. There's spare wires in the cable to route it to the host. As I said it would also need level conversion to interface to the hosts RS232 port. I believe the DCD input is commonly used for the PPS signal.

stephenw10

Without PPS you are really losing much of the benefit of GPS ntp sync. Those are cheap but the USB connected GPS devices (which cannot do PPS) are more convenient.

Steve

ajm

@stephenw10:

Without PPS you are really losing much of the benefit of GPS ntp sync. Those are cheap but the USB connected GPS devices (which cannot do PPS) are more convenient.

Indeed. The OP was aimed at those who aren't averse to some tinkering, and maybe gain some satisfaction from building their own solutions cheaper than commercial options. Some of the reasons I use pfSense actually. More here:

http://www.catb.org/gpsd/gpsd-time-service-howto.html

stephenw10

No argument from me. If I had something with a spare serial port I'd probably buy one. ;D

Steve