Commercial broadcast station carrier accuracy - Page 1
Forum section: electronics / rf-microwave

author: mark03
author_rank: Frequent Contributor
timestamp: December 17, 2018, 12:58:42 am
content: Does anyone know what is standard practice nowadays for setting the carrier frequency of commercial broadcast stations? Are they typically GPS locked? If so, I'm wondering how good a "poor man's" BCBDO (AM broadcast-band disciplined oscillator) could be.

author: ferdieCX
author_rank: Regular Contributor
timestamp: December 17, 2018, 01:07:15 am
content: Mi information could be wrong or outdated, but AFAIK for broadcast AM the maximum carrier deviation allowed is +/- 20 Hz and for FM it is +/- 2 KHz

author: babysitter
author_rank: Frequent Contributor
timestamp: December 17, 2018, 08:28:07 am
content: Some (S/W) stations were advertised as standard frequency distribution in the past, eg.. the british Droitwich or the german Donebach (Which is inactive.) The french have Allouis, which was a mixed voice+time distribution program and now is time distribution only, guess they have a nice carrier, too. I guess all german public radio was quite good, back in AM days. Your national keeper of all the standards might tell you about your area.

author: mark03
author_rank: Frequent Contributor
timestamp: December 17, 2018, 06:09:21 pm
content: I know that the telecom authorities (FCC in the US) set standards for frequency deviation. For my purposes, though, the situation only becomes "interesting" if it has become widespread practice for radio stations to GPS-lock their carriers, perhaps because that is the cheapest/easiest way of complying with the [vastly looser] regulatory requirement.According to this page,https://www.qsl.net/kd2bd/fmt-methodology.htmlWCBS seems to have a GPS-locked carrier. I figured there must be some station engineers lurking on this forum who could say if this is now standard practice.Basically, I want to know if there are effectively other atomic-derived frequency standards besides the national time+frequency stations like WWVB. If most people in the US, for example, are within ground-wave range of an AM broadcast station with GPS-locked carrier, a simple frequency standard derived from that could be a fun project. Particularly if WWVB goes away.

author: ejeffrey
author_rank: Super Contributor
timestamp: December 17, 2018, 06:44:33 pm
content: No idea, but it also wouldn't be hard to test a bunch of local stations against a GPS reference and find out.

author: cncjerry
author_rank: Unknown
timestamp: December 18, 2018, 01:16:34 am
content: AM is +/- 20 hz, or was a year ago. In the AM Stereo days the stations generally used GPSDOs to stay on frequency. When the stereo equipment was retired many pulled the GPSDO equipment out. In the SF Bay area there are still a few stations that must be using GPSDOs as I was measuring them regularly and found a few that were good to .1hz or better. I talked to a local engineer that covered a number of stations and if I can find his email which had a lot of good info on this subject, I'll post it here. I found the engineers I talked with when I was investigating this to all be very open to discussing this and other topics.Jerry

author: David Hess
author_rank: Super Contributor
timestamp: December 18, 2018, 08:27:01 pm
content: Network stations used to be locked to a frequency standard to allow them to interoperate and could be relied on to provide good accuracy. That is no longer the case because there are better ways now but that means their frequency accuracy is questionable beyond what the FCC requires.

author: BigMark
author_rank: Contributor
timestamp: December 30, 2018, 11:55:13 am
content: Quote from: mark03 on December 17, 2018, 12:58:42 amMost use GPS reference. In the past it was either oven crystal oscillators or standard crystal oscillators.