GPS Clock Project

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Josh(KF4BF)
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GPS Clock Project

Post by Josh(KF4BF) » Fri Dec 29, 2017 11:02 pm

In the "old days" GPS receivers connected to your computer using RS-232 cables. One of the RS-232 pins provided a highly accurate 1 HZ pulse, accurate to (i.e. +/- 3.0x 10EE-06 seconds or +/-3 micro seconds).

Now days inexpensive GPS receivers connect via USB, and the 1 HZ pulse pin is gone.

GPS receivers and clocks are available that provide this highly accurate 1 HZ pulse. The least expensive I can find is $1000 USD.

I need a highly accurate (inexpensive) 1 HZ pulse signal I can superimpose over a 80 meter ham band SSB audio signal received at 3 different locations to make a non-directional location finding system using triangulation.

SSB (single side band) signals have a suppressed carrier, so signal strength nulling direction finding is impractical. When receiving a SSB signal, there is no carrier, so the S-meter fluctuates wildly depending on the modulation level.

An alternate direction finding technique using signal arrival times is possible knowing time accurately, and is independent of signal direction.

An inexpensive GPS receiver clock would make a great project for rtl-sdr.com

snn47
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Re: GPS Clock Project

Post by snn47 » Sat Dec 30, 2017 2:35 am

Josh,
Do you have a source for the 1 Hz out on PS2 that you can post, was it only special chipsetset like SIRF 3 or SIRF4? I gave my NL-603P to a friend long ago and will ask him next week if he still has it.

I just checked a number of PS2 GPS mouses are still on sale in Europe e.g.
- Navilock NL-403P GPS-Receiver seriell (60109) https://geizhals.de/?fs=NL-603P&in=
- the Navilock NL-8003P GPS/​GLONASS/​BEIDOU/​GALILEO/​QZSS Empfänger, 1.5m seriell (62525) https://geizhals.de/?fs=NL-603P&in=
- NL-603P https://www.conrad.de/de/gps-empfaenger ... 30021657:s are still on sale in Europe.

Then there is the GARMIN GPS 18x 5Hz (manufacterer ref 010-00321-37) which provides 5 Hz https://geizhals.eu/garmin-gps-18x-lvc- ... 06962.html

If you look for https://www.inventeksys.com/products-page/gps-modules/ they had a http://www.inventeksys.com/wp-content/u ... ief_r1.pdf which offers also a 5 Hz out. So I wonder if the 1 Hz/5 Hz Signal is not part of all GPS-modules an if yes, if there is not a way to tap internally in an discarded GPS, like from Garmin, to get the signal.

Which accuracy do you want to achieve your position? The geometry of using just 3 signals would allow accuracy only in certain area, did you think about propagation path anomalies and multipath, an the impact of phase jitter?
vy 73
_.. .._. ..... .__. _.__

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Josh(KF4BF)
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Re: GPS Clock Project

Post by Josh(KF4BF) » Fri Jan 12, 2018 3:57 pm

http://aprs.gids.nl/gpskit/gps-readme.html

It uses the Rockwell Jupiter GPS module (no longer available).

Pins of interest on it are Pin 19 and Pin 20.

Following was copied from the website above:

pin 19
1 PPS (puls per second) signal. This is a TTL signal with a frequency of exactly 1 Hz. The pulse length is exactly 25.6 ms and the rising edge is within 1us from the UTC second transition. There is software available that synchronizes the time in your PC and that expects a 1pps signal on the DCD line, so if you make an interface yourself you could use this.

pin 20
10 kHz TTL signal. This signal is also synchronous with pin 19 and has a long-term accurate to 1uHz (microhertz) or better, if the receiver has a "fix" on the GPS satellites.

There was a guy in UK selling this receiver in a nice little metal box for about $500US several years ago. Current USB based GPS receivers are less than $40US including software. What gives?

It would be real nice having this pulse accuracy for under $50US.

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Josh(KF4BF)
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Location: South Carolina, USA

Re: GPS Clock Project

Post by Josh(KF4BF) » Fri Jan 12, 2018 4:10 pm

Hmmm, just found this receiver for $39US, but by time you order accessories and antenna, it around $50US.

It does not say how stable the clock pulse Pin is, but its very interesting! Just found it.

https://www.adafruit.com/product/3133?g ... gJA8vD_BwE

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Josh(KF4BF)
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Re: GPS Clock Project

Post by Josh(KF4BF) » Fri Jan 12, 2018 5:25 pm

SOLUTION REALIZED!

After reading the DATA SHEET on the PA6H GPS Module used in the Adafruit receiver, here is what I found on its PPS accuracy:

1.5 1PPS
A pulse per second (1 PPS) is an electrical signal that very precisely indicates the start of a second.
Depending on the source, properly operating PPS signals have typical accuracy ranging 10ns.
1 PPS signals are used for precise timekeeping and time measurement. One increasingly common
use is in computer timekeeping, including the NTP protocol. A common use for the PPS signal is to
connect it to a PC using a low-latency, low-jitter wire connection and allow a program to synchronize
to it:
PA6H supply the high accurate 1PPS timing to synchronize to GPS time after 3D-Fix.
A power-on output 1pps is also available for customization firmware settings.

BackHive
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Joined: Wed Sep 02, 2015 10:48 pm

Re: GPS Clock Project

Post by BackHive » Mon Jan 15, 2018 1:33 am

Josh,
I would be very interested in building a project like this but I'm no way as electronic savvy as you appear to be. It would be great if you would post details on here as your project develops.
Many thanks.
B/H

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Josh(KF4BF)
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Location: South Carolina, USA

Re: GPS Clock Project

Post by Josh(KF4BF) » Mon Jan 15, 2018 11:26 pm

This YouTube clip provides an excellent overview of the requirements of these modern inexpensive GPS modules:

https://www.youtube.com/watch?v=FmdG66kTfsI

rrobinet
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Re: GPS Clock Project

Post by rrobinet » Wed Nov 07, 2018 6:39 am

Look at the TDoA extension of the KiwiSDR to see triangulation by GPS derived time of arrival.

BackHive
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Joined: Wed Sep 02, 2015 10:48 pm

Re: GPS Clock Project

Post by BackHive » Thu Nov 08, 2018 9:04 pm

Josh,
Are you aware of these products.. quite popular with guys that need a stable frequency reference and timing for radio stuff...
http://www.leobodnar.com/shop/index.php ... &cPath=107
http://www.leobodnar.com/shop/index.php ... cts_id=272

Also, search ebay etc. for cheap but cool Ublox GPS USB devices.... not sure of the pinouts but they might suit your needs ?

Terry

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