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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