Boy Talk about a great write up on station stability. I thought that there might be some AMs that were GPS locked. So in reality if the ole US Government wanted a cheap backup freq dissemination they might easily have it after all with a bit of thought. (Sorry. I used a silly concept)
That certainly would be an approach thats easily implemented. As for the offsets. If they are known I do not feel they are that much of an issue today. Seems like we have a lot of tricks in the bag such as DDS etc. Time might be transmitted on a subcarrier... Or could it be sent on the main carrier slowly? Alas all silly talk accept for actually looking at and monitoring one of the suggested stations. Time to warm up a HP 3586 locked to GPS and spectrumlab for some fun Regards Paul WB8TSL On Thu, Oct 13, 2011 at 10:38 AM, Mike Seguin <[email protected]>wrote: > We don't have any AM stations, but the big reason for GPS locking of our FM > stations for IBOC is to stabilize diversity delay. > > The Analog component of the audio for HD-1 is delayed to synchronize with > the digital components so that if the digital carriers are lost, an IBOC > receiver will "blend" back to Analog. If it's not synchronized with in a few > samples, you hear a jump in the audio. > > Mike - Vermont Public Raido Engineering > > --- > 73, > Mike, N1JEZ > "A closed mouth gathers no feet" > > > On Thu, 13 Oct 2011 07:27:02 -0700, Burt I. Weiner wrote: > >> There are some AM broadcast stations in the U.S. that are GPS >> referenced. This has primarily come about as a result of Digital >> (IBOC) Broadcasting. I do off-air frequency measurements for many >> stations, primarily in the Southern California area, so I have a >> fairly good idea of who in this area is doing what and their reference >> reliability. In my local area there are three AM stations that are >> reliably referenced to GPS most of the time. They are: KFWB 5,000 >> Watts non-directional on 980 kHz, KNX 50,000 Watts non-directional on >> 1070 kHz, and KDIS 50,000 Watts directional on 1110 kHz. These >> three stations seem committed to the IBOC system, but for how long, >> who knows. There are other's, but with them it is sort of an on again, >> off again situation. A couple of caveats are that these stations may >> not always be operating on their GPS referenced exciter or >> transmitter. These days, individual transmitter maintenance is mostly >> done during the daytime and only antenna repairs are generally done >> during the nighttime hours. >> >> Not all stations broadcasting digital IBOC are GPS locked. >> Supposedly being GPS locked would allow receivers that are GPS locked >> to lock up faster and stay locked better. So far I don't know of a >> single IBOC receiver that has the capability of being GPS referenced, >> so the GPS referenced transmitter has never been of great importance. >> I know of several AM stations that have the capability but have never >> bothered to hook up the GPS antenna to their GPS capable exciter and >> really have no interest in doing so. In many cases, AM stations have >> shut down their IBOC systems due to lack of interest on the part of >> the listening radio audience and in some cases due to adjacent channel >> interference caused by the digital sidebands. In some cases they've >> actually removed the equipment from their racks and are using it, >> appropriately enough, as something to sit on. >> >> So, the bottom line is that while there are some GPS referenced AM >> broadcast stations out there, they are not a reliable day to day >> reference. >> >> Another aspect of this whole thing is that while it would be simple >> enough to GPS lock/reference an AM broadcast transmitter, this may not >> always be desirable. Having two co-channeled stations precisely on or >> very near the same frequency, even though they may be thousands of >> miles apart, can have serious fade issues. If they are exactly on the >> same frequency they can cause deep nulls in their coverage depending >> on the relative signal strengths. Paging transmitters have in the >> past gone to precision offsets of a only a few Hz in order to get what >> they called "rolling fades. While this may be desirable for paging >> systems where data can be repeated several times, it can be very >> annoying in the broadcast radio world. A listener, depending on >> location, could hear consistent deep cyclic fades. As most of you >> know, AM broadcast stations are allowed a carrier tolerance of +/- 20 >> Hz. Co-channel fades are much more tolerable to the listening >> audience if they are in the range of 15 to 20 Hz. While this 15 to 20 >> Hz offset may cause some low frequency intermodulation (tone) in the >> audio, it is much less objectionable than a deep, fraction of a Hertz >> difference causing a station to slowly come and go. Because of this I >> have several clients that have deliberately opted to go with an offset >> of 10 to 15 Hz, depending on the absolute frequency of an interfering >> co-channel station. While broadcast engineers are a scientific bunch, >> they are never the less in "Show Business", and the need to present >> their programming (such as it is) in the most listenable manner comes >> first. >> >> Burt, K6OQK >> >> >> Well its a funny thing actually. Looking at an amateur effort its not all >>> that hard at 1.6-7.0 MHz to generate reasonable power of say 100-500 >>> watts. >>> Certainly its not hard to create an exciter at those frequencies that are >>> derived from a quality reference. Heck many time nuts have CS references >>> etc. the concept is quite flexible if you consider adding some pahse >>> modulation perhaps. All in all pretty do-able. A few things tend to get >>> in >>> the way like rules and regs etc. >>> But there is an alternate that would be very reasonable. The broadcast >>> band >>> AM transmitters run all the time and if their exciters were controlled by >>> the reference you would have major portions of large areas covered. The >>> Broadcasters are already paying for the power, transmitter, and antenna >>> upkeep. >>> Of course nothing like that would happen and am modulation can have >>> effects >>> on the carrier. >>> Regards >>> Paul >>> WB8TSL >>> >> >> Burt I. Weiner Associates >> Broadcast Technical Services >> Glendale, California U.S.A. >> [email protected] >> www.biwa.cc >> K6OQK >> >> >> ______________________________**_________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/** >> mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> >> and follow the instructions there. >> > > > > ______________________________**_________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/** > mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
