WWV Time Correction Option



With a short-wave receiver tuned to one of the WWV time signal stations (2.5Mhz, 5.0Mhz, 10.0Mhz and 15.0Mhz) it is possible to keep WinSDR's (and your event files), time to within +-20 milliseconds. This is done by taking the audio out of the receiver, usually from the external speaker or earphone jack, and connecting it to the WWV Input connector on the Serial Output A/D board. Please note that this timing option is only available on older Version I and Version II ADC boards. 

How it works:

Every minute (except at the top of the hour) WWV broadcasts an 800 millisecond 1000Hz tone. On the A/D board, if you purchased this option, there is a phase locked loop tone decoder with a bandpass filter tuned to 1000Hz. This 800 millisecond tone burst is uses to keep track of time on the A/D board.

Short-wave Receiver and WWV:

The short-wave receiver should be a digital type so it will stay tuned to the WWV station you select. Radio Shack has a portable digital receiver for around $80.00 (Model DX-375). You will probably need to have an external antenna. This can be a long piece of wire run between two trees or on top or your roof. For WinSDR to keep correct time, it needs to have fair reception to one of the WWV frequencies for a few hours each day. You most likely will not get 24 hour reception on any one WWV frequency. At my location I get best reception on 5.0Mhz at night and during the day 10.0Mhz or 15.0Mhz. I normally keep my receiver tuned to 5.0Mhz because I get better, and longer, reception at night.

Using the WWV Option:

Before starting WinSDR, you need to set the time and date on your computer system to within 15 seconds of local time. You can do this by listening to WWV and setting the time at the top of the minute. After setting the time, start up WinSDR. WinSDR will read the time from the system and send it to the A/D board. It is important too remember that the only information the A/D board gets from WWV is the minute mark. You must set the system date and time to +- 15 seconds of local time for the time to lock and have good time information for your event files.

After starting up WinSDR, and connecting the audio to the A/D board, you will need to adjust the audio level on the receiver. First open the Log File Viewer by using the View / Log File / View Log File menu items. This will display the status of the time keep information and other debug messages. The messages also written to a file called WinSDR.log.

To enable the WWV timing option in WinSDR, go to the System Settings dialog box and select WWV in the Time Reference Type drop down box. 

Start with the volume control about 1/3 of the way up. At the top of the minute you should see the following sequence on the Log File Viewer:

02/15/02 15:39:01 WWV - Not Locked - Lock Count:1 Diff:435ms
02/15/02 15:41:01 WWV - Not Locked Count:2 Width:812 Diff:423ms Avg:432ms Set:1
02/15/02 15:43:01 WWV - Not Locked Count:3 Width:828 Diff:436ms Avg:427ms Set:1

The format of each line is:

Date/Time of message.
Not Lock Count: Number of good locks.
Width: Width of the 800 ms pulse detected by the tone decoder.
Diff: This is the current 800 ms pulse start offset in time from the running average.
Avg: This is the running average of the start of the 800 ms pulse.

When the Not Locked Count gets to 6, the system will be locked to WWV. This process may take from 6 to 10 minutes, if you have very good reception, to several hours if you have poor reception. If you are not getting any time messages, and you are getting good reception to WWV, you should increase the volume a little. At some point on the volume control you should start to see the time messages. This will take some time and patience. 

When WinSDR is locked you will see the following messages on the debug line:

02/15/02 17:35:01 WWV-  Lock Time:1 01:23 Locks:4/12 Diff:3ms Avg:-4ms
02/15/02 17:38:01 WWV - Lock Time:1 01:26 Locks:5/12 Diff:-10ms Avg:-3ms
02/15/02 17:39:01 WWV - Lock Time:1 01:27 Locks:6/12 Diff:-8ms Avg:-4ms
02/15/02 17:42:01 WWV - Lock Time:1 01:30 Locks:8/12 Diff:-1ms Avg:-4ms
02/15/02 17:42:01 WWV - Lock Time:1 01:30 Locks:8/12 Diff:-1ms Avg:-4ms

The format of each line is:

Date/Time of message.
Lock Time: The time in days, hours, and minutes that WinSDR is locked to WWV.
Locks: Current number of good 800 ms pulses / last number of good pulses. This is updated every 15 minutes.
Diff: The current pulse start offset in time from the running average.
Avg: The running average of the start of the 800 ms pulse.

One Second Output:

The CPU module on the A/D board produces a one second output square wave on pin 12 of the DB-25 connector. The rising edge of this output marks the beginning of each second. You can use this output to monitor how well the A/D board is keeping track of time. If you have an oscilloscope you can monitor this output and compare it to some other reference. One reference can be the audio output from your WWV receiver and comparing it to the 1 second tick you hear (this tick is 5 cycles a 1000hz) and seen on the oscilloscope.

Simulating the WWV Signal:

If you have access to another time source, you can simulate the WWV signal. You can then feed a one pulse per minute TTL signal into TP 1 on the A/D board. The digital signal needs to be an 800 millisecond (+/- 20 milliseconds) pulse that is normally high (+5VDC) and goes low (0VDC) at the top of the minute. See the example below:
     +5 --------------------              -----------------------------
          Top of minute -> | <- 800 MS -> |            Next minute ->  |
      0       mark         ----------------               mark         -------...

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