Omega shut down 30 September 1997! Here's an edited copy of my report e-mailed to a few other people and also a spectrogram made of the tape right after (this has been updated 03 January 2012 with recording and another spectrogram):
Well, I got a nice recording of Omega's last beeps 30 Sept. 1997 at 0300z, and also two nights of nice whistlers too, especially this morning, 01 October 1997, between 1100-1330 UT. There was also some intermittant dawn chorus starting at about 1230 UT and going until after 1500 UT - I had not yet caught chorus this summer or fall until now, so I was really glad to hear some chorus even though it was not very strong, and overall a really nice 2 days of whistler listening. Many whistlers this morning (October 01) had echoes too. The whistlers seemed to be generated by fairly nearby lightning - not too local but within 1000 miles.
I started recording at 0257 UT 30 Sept. I made a WWV time check at 0259z on the tape and then let it run with the WR-4b whistler receiver set to high-pass--lots of Omega into the Marantz PMD-212 tape recorder. At about 0259:30, Omega D (North Dakota) shut down, leaving Omega-C Hawaii going for about 2-3 more of its cycles. About 0300 (or within a few seconds) and after its two 11.8 kHz beeps, Omega C went off. Both D and C did not shut off abruptly, but did a sort of 'fade-out' over a 1-2 second period. Interestingly, going over the tape in slow motion revealed a third, very weak Omega station running on until a minute or so later - the 10.2 kHz beep was noticed. Probably H-Japan, the next strongest station here in Califirnia usually.
By 0301 UT, all that was left was the Russian Alpha system - short beeps in clusters of three beeps, a pause, then three beeps again in downward frequency steps. Russian Alpha is much weaker and higher up in frequency (up to 14.1 kHz) then Omega was and has a far lower duty-cycle, and so the natural radio band is really MUCH cleaner sounding suddenly! It's also fun to observe Alpha propagation - I guess the strongest one I get is from Siberia (KO - see ALPHA article this link)--it is stronger toward sunrise than at any other time of the day by 3-6 dB or so.
The spectrogram above shows Omega Station "D" North Dakota, and Omega Station "C" Oahu, Hawaii with their last beeps. Recorded on my van-based WR-4b VLF receiver with 2 meter whip antenna up 3 meters high. The tape was made on a Marantz PMD-212 with cromium tape and the WR-4b in high-pass/emphasis mode.
The tape was copied into a sound file at 44.1 kHz/16 bit. Then it was FFT filtered in Coolwave 1.5 and 9 to 14 kHz was emphasised by 15 dB. Then I ran a spectrogram on it and then edited the spectrogram adding the labels.
Originally written in Dec. 1997; revised April 2007