Discussion:
Linux GPS time update program
(too old to reply)
ron.eike2-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org [linuxham]
2014-09-26 20:01:13 UTC
Permalink
Raw Message
I have heard that digital modes like JT65 and JT9 need extremely accurate time. What linux utilities will do this online and also using GPS in the field?

Ron - KA3PSO
Larry DiGioia n8ku-b2rNdqnAlKpWk0Htik3J/w@public.gmane.org [linuxham]
2014-09-26 20:03:55 UTC
Permalink
Raw Message
I heard this too and was troubleshooting it by making the time
super-perfect, until I finally saw in the documentation that it only
needs to be within one second.
Post by ron.eike2-***@public.gmane.org [linuxham]
I have heard that digital modes like JT65 and JT9 need extremely
accurate time. What linux utilities will do this online and also using
GPS in the field?
Ron - KA3PSO
Jeff Francis™ jeff-CDdbmnNP9qodnm+yROfE0A@public.gmane.org [linuxham]
2014-09-26 20:06:43 UTC
Permalink
Raw Message
Some variant of ntp (depends on which linux you're using, but ntp, ntpd,
and openntpd are all common). Note that ntpdate is not the same thing.
ntpdate queries an ntp server one time, and sets the date. The various
flavors of ntpd continuously talk to ntp servers and keep your clock in
sync forever (well, as long as you're connected). They can also be
configured to learn your internal clock drift and automatically correct
your time even when your network is down. For keeping time set with a GPS,
see this article:

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

I expect Eric mentions it (haven't read his howto in years), but gps
receivers with binary protocols are more accurate for setting time than
those that spew NMEA-0183.

Jeff N0GQ
Post by ron.eike2-***@public.gmane.org [linuxham]
I have heard that digital modes like JT65 and JT9 need extremely accurate
time. What linux utilities will do this online and also using GPS in the
field?
Ron - KA3PSO
--
-=jeff=-
John Nogatch jnogatch-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org [linuxham]
2014-09-26 20:54:50 UTC
Permalink
Raw Message
Post by ron.eike2-***@public.gmane.org [linuxham]
I have heard that digital modes like JT65 and JT9 need extremely accurate time. What linux utilities will do this online and also using GPS in the field?
You probably already have ntp installed:
$ dpkg -l ntp
... ii ntp 1:4.2.6.p5+dfsg-3ubuntu
amd64 Network Time Protocol daemon and utility
programs

When the ntp daemon is running, it updates your system time, based on
Internet communication with time servers:
$ ps -eafl |fgrep ntpd
5 S ntp 1802 1 0 80 0 - 8376 poll_s Sep24 ?
00:00:23 /usr/sbin/ntpd -p /var/run/ntpd.pid -g -u 105:110

If you are not connected to the Internet, then "gpsd - Global
Positioning System - daemon" can be used to obtain time from a GPS
connected to your computer. I have found that inexpensive "puck" GPS
with USB connection will work, but the jitter is worse than the older
units that have RS-232 serial connections.

Google search for "ntp gpsd" will turn up more info, e.g.
http://www.catb.org/gpsd/gpsd-time-service-howto.html#_references

You can also see in the waterfall display, that most of the JT-65 and
JT-9 transmissions are starting on the minute boundary, and ending at
the 50 sec point. It is obvious when someone does not have their clock
set correctly.

-John AC6SL


------------------------------------
Posted by: John Nogatch <jnogatch-***@public.gmane.org>
------------------------------------
Steve K0STK k0stk-WYrOkVUspZo@public.gmane.org [linuxham]
2014-09-27 19:12:23 UTC
Permalink
Raw Message
Post by John Nogatch jnogatch-***@public.gmane.org [linuxham]
If you are not connected to the Internet, then "gpsd - Global
Positioning System - daemon" can be used to obtain time from a GPS
connected to your computer. I have found that inexpensive "puck" GPS
with USB connection will work, but the jitter is worse than the older
units that have RS-232 serial connections.
Primarily because a timing RS-233 GPS outputs both NMEA sentences (which
label the seconds) and a PPS signal (which marks the beginning of each
second). A good timing GPS will have a PPS signal within +/- 1
microsecond (us) of UTC.

USB GPS receivers, on the other hand, only output NMEA sentences over a
jittery packetized transport layer. NMEA sentences are sent out when
ever the receiver is not otherwise busy and can have up to +/-.5 second
jitter.
--
73, Steve K0STK // k0stk-***@public.gmane.org



------------------------------------
Posted by: Steve K0STK <k0stk-***@public.gmane.org>
------------------------------------
Jeff Francis™ jeff-CDdbmnNP9qodnm+yROfE0A@public.gmane.org [linuxham]
2014-09-28 15:56:45 UTC
Permalink
Raw Message
If you do have a USB "hockey puck" GPS, you can maximize accuracy by
making sure it's sending data in it's proprietary binary mode rather than
NMEA-0183. Neither is great, but the former is better than the latter (and
gpsd will try for the former before falling back to the latter, unless
you've fiddled with your GPS settings and disabled binary mode). If you
truly care about accuracy, get an RS-232 serial reciever with a 1PPS output
(and wire up the 1PPS output properly).

Jeff N0GQ
Post by Steve K0STK k0stk-***@public.gmane.org [linuxham]
Post by John Nogatch jnogatch-***@public.gmane.org [linuxham]
If you are not connected to the Internet, then "gpsd - Global
Positioning System - daemon" can be used to obtain time from a GPS
connected to your computer. I have found that inexpensive "puck" GPS
with USB connection will work, but the jitter is worse than the older
units that have RS-232 serial connections.
Primarily because a timing RS-233 GPS outputs both NMEA sentences (which
label the seconds) and a PPS signal (which marks the beginning of each
second). A good timing GPS will have a PPS signal within +/- 1
microsecond (us) of UTC.
USB GPS receivers, on the other hand, only output NMEA sentences over a
jittery packetized transport layer. NMEA sentences are sent out when
ever the receiver is not otherwise busy and can have up to +/-.5 second
jitter.
--
--
-=jeff=-
David Ranch linuxham-fld-U76wwbNhhF3R7s880joybQ@public.gmane.org [linuxham]
2014-09-26 21:26:01 UTC
Permalink
Raw Message
In the field, without Internet access, you can get gpsd running to get
time from your connected GPS.

--David
KI6ZHD
Post by ron.eike2-***@public.gmane.org [linuxham]
I have heard that digital modes like JT65 and JT9 need extremely
accurate time. What linux utilities will do this online and also using
GPS in the field?
Ron - KA3PSO
Loading...