PSN-L Email List Message
Subject: Re: Computer Timing Problems / Solutions
From: Larry Cochrane lcochrane@..............
Date: Sat, 16 Apr 2005 16:30:32 -0700
The time stamping of the data is done on the A/D board. If you have a time reference
like GPS the time accuracy is one or two milliseconds. The board uses a 1 millisecond
interrupt so the timing can't be any better then one ms. With WWV and WWVB the
accuracy will be in the order of +-10 to +-20 ms depending on the signal quality.
If you have a time reference connected to the A/D board WinSDR can use the A/D
board's time to keep the PC's time accurate to +- 250 ms. Since the time stamping is
done on the A/D board there is no need to keep the PC's time accurate to less then a
few seconds. WinSDR does use the system's time for things like file names so the PC's
time should be near the A/D board's time.
If there is no timing reference available for the A/D board you can use the PC's
time. In this mode the A/D board requests the current time from the PC every minute
or so and uses this time for data time stamping. If the PC's time is keep accurate
with a program like NTP the overall accuracy can be +- 30 or +-50 ms or about the
same as WWV/WWVB.
With regard to the different time references. By far GPS is the best, if you can find
a location for the antenna that will allow the receiver to see two or more satellite
most of the time. The cost of a OEM GPS receiver with a 1 PPS signal is now below
$100.00 USD. I am now selling the Garmin GPS 18
(http://www.garmin.com/products/gps18oem/index.jsp) for this price. This is a very
nice receiver that works very will with my A/D board. Given that the cost to use GPS
keeps going down I not sure I see the need to support WWV/WWVB any more. The other
problem is these signals are only available here in the States. Since half of my
sales are overseas a lot of people will not be able to use this feature. And with
most of the PSN station having a full time Internet connection now a days they always
have the option to use NTP etc as a time reference.
Redwood City, PSN
> Larry, I would like to suggest that you give consideration to providing
> the 16-bit Serial Output A/D Board for WinSDR with an option to receive and
> fully decode WWVB signals, or the ability to read the output of a MCM
> microcontroller module. I have read your note, dated 1998, on WWVB signal reception.
> I note that the serial board can currently use WWV minute tone decode
> signals, but you state that 'You will not get 24 hour reception on any one
> channel, as long as you can get 4 to 6 hours per day will be fine. At my location
> I get best reception on 5.0Mhz at night and during the day 10.0Mhz or
> Does the timing for SDR originate on the board, or is it dependant on
> the computer clock, please? My computers can NOT keep time over a timing break
> of maybe 12 hours, to better than about 2 sec. This is certainly NOT good
> enough for seismic work! Unlike WWV, WWVB has the potential to provide accurate
> timing signals over the full 24 hrs for most places in the USA. The extreme
> range daytime WWVB signal is certainly a lot weaker than the nightime signal,
> but with the possible exception of Maine, it should be satisfactory
> The ability to fully decode the WWVB signal could cope with the
> situation of a power outage. It wasn't until I bought a 60 KHz radio corrected
> digital clock that I realised just how bad my computer timing systems were! Another
> reason for doing this is to provide a timing system totally independant of
> the www. There are already predictions of future communications problems on
> the web.
> The total cost could well be about that of just a GPS ANTENNA !
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