Re: [time-nuts] Best Chance GPS module
On 30/11/2016 4:23 PM, Bob Camp wrote:
- Unless you can reasonably expect 4 sat’s in view at all time, don’t bother with setting up a GPS
timing system. It will just make you angry with all the issues.
I'm hoping a timing GPS module, with their claims of being successful
(to the precision I need anyway) on few, or even a single sat. Finger's
crossed.
A USB GPS on your PC will give you a pretty good idea of what you can or can’t pick up.
Great idea!
Thanks!
From: MLewis
I'm hoping a timing GPS module, with their claims of being successful
(to the precision I need anyway) on few, or even a single sat. Finger's
crossed.
---=
Yes, that's what I thought as well, until I bought and tested one and found
out that - in practice - they need an even /better/ set of GPS signals than
a simpler position GPS/PPS.
With a GPS/PPS even Windows can get within 1 millisecond, particularly with
Windows-8 or 10:
http://www.satsignal.eu/mrtg/performance_ntp.php#windows-stratum-1
I monitor the comp.protocols.time.ntp Usenet group and would be happy to
continue there.
Cheers,
David
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv
On Thu, Dec 1, 2016 at 6:30 AM, David J Taylor <
david-taylor@blueyonder.co.uk> wrote:
Yes, that's what I thought as well, until I bought and tested one and
found out that - in practice - they need an even /better/ set of GPS
signals than a simpler position GPS/PPS.
Since that's not my experience (even with poor antenna position) I'm
curious which unit you were using.
Yes, that's what I thought as well, until I bought and tested one and
found out that - in practice - they need an even /better/ set of GPS
signals than a simpler position GPS/PPS.
Since that's not my experience (even with poor antenna position) I'm
curious which unit you were using.
---=============
Paul,
Venus838LPX-T. Seems to go into a non-locked state for a proportion of the
time but still emits a PPS signal, which increasingly deviates from true
UTC. That's using a 25 mm square 28 dB active patch antenna, similar to the
antennas on other similarly located GPS receivers. This was indoors, on the
top floor of a two-storey building, with just the power fed to it, watching
the LED flash.
Maybe I was unlucky? I wonder what experience others have?
Cheers,
David
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv
Was the LED on the PPS pin or on the FIX pin?
The FIX pin is nothing like the PPS output. Frankly, I’m not 100% sure what the rules are for it. When things are working properly, it blinks at 0.5 Hz, but the leading and trailing edges are something like 120-150 msec after the second. It’s very, very loose. My own interpretation is that the controller flips the bit when it’s got nothing better to do.
I’ve not witnessed the actual PPS pin being toggled when GPS isn’t available, but it’s not a failure mode I’ve expended a lot of effort to examine.
On Dec 1, 2016, at 7:44 AM, David J Taylor david-taylor@blueyonder.co.uk wrote:
Venus838LPX-T. Seems to go into a non-locked state for a proportion of the time but still emits a PPS signal, which increasingly deviates from true UTC. That's using a 25 mm square 28 dB active patch antenna, similar to the antennas on other similarly located GPS receivers. This was indoors, on the top floor of a two-storey building, with just the power fed to it, watching the LED flash.
Maybe I was unlucky? I wonder what experience others have?
On Dec 1, 2016, at 7:44 AM, David J Taylor david-taylor@blueyonder.co.uk
wrote:
Venus838LPX-T. Seems to go into a non-locked state for a proportion of
the time but still emits a PPS signal, which increasingly deviates from
true UTC. That's using a 25 mm square 28 dB active patch antenna, similar
to the antennas on other similarly located GPS receivers. This was
indoors, on the top floor of a two-storey building, with just the power
fed to it, watching the LED flash.
Maybe I was unlucky? I wonder what experience others have?
From: Nick Sayer via time-nuts
Was the LED on the PPS pin or on the FIX pin?
The FIX pin is nothing like the PPS output. Frankly, I’m not 100% sure what
the rules are for it. When things are working properly, it blinks at 0.5 Hz,
but the leading and trailing edges are something like 120-150 msec after the
second. It’s very, very loose. My own interpretation is that the controller
flips the bit when it’s got nothing better to do.
I’ve not witnessed the actual PPS pin being toggled when GPS isn’t
available, but it’s not a failure mode I’ve expended a lot of effort to
examine.
---==================
Nick,
I had to dig out the module to check, but as far as I can tell the LED is
connected to pin 7 on the chip, listed as GPIO0/LED on the data sheet.
Nominally, navigation status.
The PPS output which I was monitoring comes from the PPS pin (40) on the
chip - GPIO3/P1PPS1
Cheers,
David
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv
Ok. It wasn’t totally clear from your earlier message what you were looking at, but just be aware that the LED pin is just a “blinkenlichten” pin that means almost nothing. You have to actually separately look at the PPS pin to see what it’s doing. There’s (almost) no connection between the activity on the two pins.
On Mar 19, 2017, at 2:13 AM, David J Taylor david-taylor@blueyonder.co.uk wrote:
On Dec 1, 2016, at 7:44 AM, David J Taylor david-taylor@blueyonder.co.uk wrote:
Venus838LPX-T. Seems to go into a non-locked state for a proportion of the time but still emits a PPS signal, which increasingly deviates from true UTC. That's using a 25 mm square 28 dB active patch antenna, similar to the antennas on other similarly located GPS receivers. This was indoors, on the top floor of a two-storey building, with just the power fed to it, watching the LED flash.
Maybe I was unlucky? I wonder what experience others have?
From: Nick Sayer via time-nuts
Was the LED on the PPS pin or on the FIX pin?
The FIX pin is nothing like the PPS output. Frankly, I’m not 100% sure what the rules are for it. When things are working properly, it blinks at 0.5 Hz, but the leading and trailing edges are something like 120-150 msec after the second. It’s very, very loose. My own interpretation is that the controller flips the bit when it’s got nothing better to do.
I’ve not witnessed the actual PPS pin being toggled when GPS isn’t available, but it’s not a failure mode I’ve expended a lot of effort to examine.
---==================
Nick,
I had to dig out the module to check, but as far as I can tell the LED is connected to pin 7 on the chip, listed as GPIO0/LED on the data sheet. Nominally, navigation status.
The PPS output which I was monitoring comes from the PPS pin (40) on the chip - GPIO3/P1PPS1
Cheers,
David
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv