Dave wrote:
I also measured some AM stations and I had drifts of 56 mHz for a 1030 KHz station, and I have measured the DSP drift as around 14 mHz. Do the AM stations really drift around that much? I thought they were pretty stable.
The FCC requirement for AM stations is +/- 20 Hz. It is not uncommon to find stations 10 Hz or more off frequency. I just checked one of the major stations here, and it is more than 16 Hz high with hundreds of mHz variation over 15 minutes.
Some stations are locked to GPS these days, but far fewer than I expect. And some that are "locked" to GPS are rather loosely coupled, so they have offsets of as much as a Hz or even more (synthesizer steps, I presume) and/or drift of +/- tens to even hundreds of mHz.
Most AM stations still use crystals in bang-bang ovens. It is often very easy to watch the oven heater cycle if you are using something with enough resolution (I generally use a spectrum analyzer with resolution in the few mHz range for such work).
This afternoon, I can see 5 carriers on 1030 +/- 20 Hz. The station closest to you (WWGB) has been about 1 Hz low over the last few hours, with about 300 mHz variation (peak to peak). The variation shows the familiar asymmetrical ramp of an oven cycling with a period of ~29 minutes. It takes ~6.8 minutes to fall from its positive peak to its negative peak (heater on), and 21.9 minutes to climb back to its positive peak (heater off).
Best regards, Charles _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
