I have been monitoring 30m to try to detect some of those MEPT (Manned Experimental Propagation Transmitters) that I wrote about a few weeks ago, without any real luck. I’ll be trying again this weekend, but since I was bored, I decided to tune down to 10.000 Mhz and try receiving the time signal. It’s sent with LOTS of power, and so is pretty easy to receive. In fact, I had to enable the attenuator and turn off the preamplifier on my FT-817nd to prevent serious clipping from occurring.
I was confused by something though. I heard both a male and female voice announcing the time: here’s the recording…
And here’s the spectrogram of the resulting signal, just for fun.
It turns out that I’m receiving two overlapping signals, one from WWV in Colorado, and one from WWVH which is in Hawaii. Typically, you can only hear one or the other. The WWVH signal is supposedly aimed away from the continental U.S. and you normally can’t hear it, but to keep them from interfering with each other when propagation is enhanced, it announces in a female voice somewhat earlier than the WWV signal does. The two “tones” they use to announce the start of the minute occur at different frequencies too. The WWVH signal also includes marine weather warnings, which you can hear at the beginning.
By tuning down to 5 Mhz, I found that I could no longer pick up the WWVH signal at all, demonstrating that propagation does indeed depend on frequency.
Anyway, super trivial thing, but I thought it was interesting. You can read a lot more about time signals at The NIST Time and Frequency Website.