[time-nuts] WWVB information

Tom Van Baak tvb at LeapSecond.com
Fri Apr 13 12:02:16 EDT 2018


So Doug's Spectracom WWVB receiver shows a green lock status. I didn't believe it, but he sent a photo. I then tried it here and the same thing happens to me. It's very suspicious because we know these old carrier phase WWVB receivers don't work with the enhanced WWVB broadcast format.

Instead of trusting the green light I measured the 5 MHz output of the WWVB-disciplined receiver using a hp 53132A. Here's an example of 1 second readings with no antenna (no lock):
4999931.22296  Hz
4999931.22650  Hz
4999931.22709  Hz
4999931.209453 Hz
4999931.21235  Hz
STD DEV: 0.007968 Hz

You see a free-running undisciplined OCXO. Not very accurate but very stable.

Then I connected the WWVB antenna. Within seconds the green lock light came on. The readings looked like:
4999994.676217 Hz
5000014.45065  Hz
4999966.61447  Hz
4999963.27949  Hz
4999971.40319  Hz
STD DEV: 15.853246 Hz

You see that the OCXO has been steered closer to 5 MHz, but the stability is horrible.

Lastly, just to check the system was working, I applied a 60 kHz carrier near the antenna using a hp 3325B. The readings look like:
4999999.9693  Hz
5000000.0199  Hz
5000000.0202  Hz
4999999.9693  Hz
4999999.9998  Hz
STD DEV: 0.02355 Hz

In this case very accurate and quite stable.

ADEV plot of all three runs is attached.

So my conclusion is the green lock light is false. The Spectracom really isn't locking to the carrier. It's trying hard, but the new phase encoding keeps this from happening. Someone can take a look at the block diagram or schematic and explain why the circuit gets fooled into thinking there is lock when there really isn't. Look for Spectracom 8161 or 8164 on ko4bb's manual site.

The one mystery is why this false green only started a week ago for Doug. If any of you have Spectracom WWVB receivers, fire then up and see what happens. I think I'll keep mine going for a few days or months and see if the false green ever goes out.

/tvb
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