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Author Topic: AM Broadcast/LW/MW frequency standards  (Read 1124 times)

Posts: 8123

« Reply #15 on: November 14, 2017, 09:46:24 AM »

There are BBC transmissions on 198 kHz at five sites in the UK. The main one is Droitwich, south west of Birmingham, (500kW): then there's two in London - 4 watts covering the inside of the Rotherhithe Tunnel, and under 1 watt covering the Blackwall tunnel (both tunnels under the River Thames), one at Westerglen  (50kW), roughly half way between Edinburg and Glasgow, and one at Burghead (50kW), on the Moray Firth in north east Scotland. The sites are all owned by a company called Arquiva: frequency is controlled by a rubidium standard.

Droitwich uses a multiple conductor  'T' antenna strung between two 700 foot masts 510 feet apart. You get a good view of it from the train from Birmingham to Bristol.

I doubt you'll get good programme quality from any of them in the US, though! But especially at sunrise and sunset, you may well get a reasonable signal from Droitwich in a narrow bandwidth. They do carry some phase encoded time information.

How about LORAN C on 100kHz?

Posts: 1254

« Reply #16 on: November 14, 2017, 01:41:14 PM »

I doubt that I'm receiving 198KHz from EU. Whatever it is, an anomaly of the RX or not, it's pretty consistent 2Hz below 198K and very stable, no modulation that I can tell. I measured WWVB and CHU this morning before the ionosphere got into the picture and started scattering things, both of them measured within 0.001 Hz of their freq over an hour or more, average. I did try an AM digital local station, WMAL from DC and it's all over the place, it's even worse than my BFO. I may try a few AM broadcast stations and see if any of them seem stable. As far as LORAN, last time I remember trying to get info on them, they're off the air, I could be wrong but I think the GPS replaced them.

There's also a 2M beacon down in central VA I can get and it's locked to the guys GPS also. I haven't tried that one, but it's got a horrible chirp on the CW signal and doesn't produce a good trace on SL. You think there would be something out of the Naval Observatory in DC, but I guess not. I'm sure they've got some special timepiece there.

I still haven't tried my Rb osc, but I've been warming it up for 2 days now. It looks like the osc locked anyhow.

I may try building a shielded tuned loop for 60KHz.

I remember reading in SpectrumLab about using the 1 pps out of a GPS to lock the sound card, but never got into it that much, plus my GPS puts out an every other second pulse. But that's also not going to help me on VLF or even HF.

Posts: 1254

« Reply #17 on: November 16, 2017, 04:00:26 PM »

I still can't find any LF through HF signal that's anywhere as stable as either my Rb osc, GPSDO or my BFO which drifts ±10mHz with the fan on/off. Since I can't find a signal as stable, I guess I can't measure anything on HF to the resolution I can actually measure. I've got SpectrumLab down to decimate by 24 and FFT input at 37K with stable output measurements down to .0001 Hz. Anything more than that takes the computer too long to process. I spent all day yesterday figuring out the Plotter function in SL. That's a project but I'm getting so I understand it and also exporting text data I can put in Excel. Talk about a learning curve.

Posts: 6496

« Reply #18 on: November 18, 2017, 08:00:22 AM »

I suspect your GPSDO is far more accurate than either WWV or WWVB, and much more accurate than any AM or FM broadcast station... but you should verify this with NIST, as they are the time keepers.
And if you are curious about FMTs, check with ARRL to know their frequency references.
AM broadcast was 20 Hz tolerance and FM broadcast was either 2000 or 3000 Hz, not the best reference nowadays.


Posts: 1254

« Reply #19 on: November 18, 2017, 07:03:15 PM »

I did determine today that my Rb osc is ~.005 Hz below my GPSDO. Now I'm a guy with 2 clocks, which one is right? I'm going to assume the GPS one is pretty close and over time it seems to agree with what I can measure. Yeah, I've not found an AM station that doesn't drift all over, worse than my BFO. Thanks!
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