Idea to improve/integrate AM-HD and FM-HD

[spt87]

Ok, ignoring all the known concerns with HD (and knowing at least someone will say the only way to improve HD is to discontinue using it), here is an idea the occurred to me while driving around NYC with a HD radio.

For stations that broadcast on both AM and an FM-HD sub channel (such as WBZ-AM and WBZ-FM HD3) or HD sub channel and a FM translator, include some data in the HD stream that the radio could utilize to leverage the AM or translator as an analog fall back. So instead of the FM-HD2 or 3 just dropping out it could leverage a simulcast analog signal just like the primary HD channel works with the analog signal on a FM or AM.

Maybe on the AM side Ibiquity could introduce a "lite mode" where only a limited datastream which pointed to FM-HD simulcasts was sent to the receiver (maybe more than one if there were multiples to allow enhanced HD coverage). This might allow AMs to operate with less or no sideband interference and potentially be C-Quam compatibility. Since the HD generally is only good in the primary coverage area a sister FM in the same area should be able to provide HD sub channel coverage while the analog listeners could enjoy wider bandwidth, less noise and maybe analog stereo as well.

I'm sure this would require new "generation 2" radios but it may make the entire system more useful. I kept experimenting and switching between WCBS-AM/WCBS-FM HD3 and WINS-AM/WWFS-FM HD3 trying to figure out which sounded the best over the weekend. Instead of doing it manually, why not let the radio figure it out and switch for me.

 

[Savage]

Basically what you're advocating is trashing the entire HD system and starting over. The firmware would require such extensive revision I would bet new hardware would be required at every station. And the few existing HD receivers would be immediately obsolete. I don't think that's gonna happen.

I don't know what you mean by "leverage the AM." You mean if the HD-2 or 3 signal dropped your receiver would default by changing bands back to AM or an analog FM translator? How does that improve the fate of AM? The mode-flipping would be immensely annoying, even worse than the AM-HD digital-to-analog defaults.

 

[spunker88]

You'd also have to make it so the radio confirmed the correct signal on the alternate channel either via RDS or HD data before tuning. Otherwise I'd be listening to say WCBS 880 one night and it would automatically flip over to the FM band where there is no signal since I'm hundreds of miles away from NYC. So basically on the AM side the radio receives digitally data along the lines "WCBS 101.1 HD-3". While still tuned to 880 the receiver checks for 101.1 HD-3 with the calls WCBS, confirms the signal and locks the HD before tuning. It could also be done with AM stations that only have analog FM signals by using RDS. AM-HD is a joke right now, interference such as lightning can disrupt the HD signal within its market. A small digital text stream kept within the 10khz signal (similar to RDS on FM) would reduce adjacent interference and dropouts like lightning wouldn't matter as much.

RDS already has a feature like this that will change between FM stations as you leave the signal of one. I imagine it checks the signal before changing channels as well. I don't know if anybody in the US uses it but it is popular in Europe.

 

[w9wi]

For stations that broadcast on both AM and an FM-HD sub channel (such as WBZ-AM and WBZ-FM HD3) or HD sub channel and a FM translator, include some data in the HD stream that the radio could utilize to leverage the AM or translator as an analog fall back. So instead of the FM-HD2 or 3 just dropping out it could leverage a simulcast analog signal just like the primary HD channel works with the analog signal on a FM or AM.

Maybe on the AM side Ibiquity could introduce a "lite mode" where only a limited datastream which pointed to FM-HD simulcasts was sent to the receiver (maybe more than one if there were multiples to allow enhanced HD coverage). This might allow AMs to operate with less or no sideband interference and potentially be C-Quam compatibility. Since the HD generally is only good in the primary coverage area a sister FM in the same area should be able to provide HD sub channel coverage while the analog listeners could enjoy wider bandwidth, less noise and maybe analog stereo as well.

That's an idea that isn't too horribly far from existing technology.

FM-RDS includes provisions for an "alternate frequency" table -- a list of other frequencies carrying the same program. It's widely used in Europe where a single FM station may cover an entire country through the use of dozens of transmitters on different frequencies. Its use is pretty rare in the U.S., but I have seen it. (and I *have* seen AM frequencies in the AF list. Obviously you can't switch back *from* AM *to* FM in the existing standard (since there's no such thing as AM-RDS) but you can apparently go the other way)

Ibiquity recently proposed a low-bandwidth data system for AM. It didn't allow for digital audio but it did have enough bandwidth to transmit an AF table. IIRC interference to *adjacent* stations would be much less (maybe even non-existent) compared to AM-IBOC, although I also seem to recall a significant risk of self-interference. (where the data would interfere with the station's own analog signal)

(alternatively, since the amount of data necessary to provide an alternate-frequency table is pretty small, one could use a lower-bandwidth data scheme, maybe a slight frequency modulation of the AM carrier)

An alternate-frequency scheme is not, to my recollection, part of either Ibiquity standard. But it wouldn't be hard to mix the two.

 

[tomservo]

RDS already has a feature like this that will change between FM stations as you leave the signal of one. I imagine it checks the signal before changing channels as well. I don't know if anybody in the US uses it but it is popular in Europe.

I've heard of it being used on a few smaller FMs with translators, and the entire Mississippi Public Broadcasting network uses it (along with HD) but other than that, I don't know of anyone.

It was kinda neat being able to drive cross-state and never lose the same NPR feed. It worked pretty well.

 

[spt87]

I guess the idea is similar to the RDS feature but would work across both bands.

As for saving AM - the best way to do that is to merge AM and FM together so no one has to switch bands. Hit scan/seek/tune and you're scanning 530 through 108.1 (with a big skip between 1710 and 88.1). Allowing HD to select the best signal would be a step toward this. Unify the preset buttons as well (my GMC Acadia radio already has unified presets like this for AM/FM/XM).

Yes, I think on the radio side it likely could not work with the current hardware - but wouldn't break them either so it would be like SiriusXM version 2 receivers where you get an additional feature.

On the transmission side it would likely be software upgrades. My thought is it would be up to each station to ensure the correct alternate frequencies were programmed into the HD exciter. So WCBS-AM would send info that WCBS-FM HD3 (101.1) is the alternate. WCBS-FM HD3 would send data indicating 880AM was an alternate. The HD radio could then decide which signal was best - if WCBS-FM HD3 would decode, it uses that, if not it fails back to WCBS-AM 880. Potentially also include the AM-HD as a choice in the selection (unless it is running in a new "lite" mode and only sending the alternate station info) and then flip to which ever is strongest - AM, AM-HD or FM-HD sub channel. I don't think this flipping is any more offensive than the current flipping between HD and analog (so long as the audio is sync'ed) and is better then the FM-HD just completely dropping out to silence.

 

[spt87]

BTW - I'm not trying to be an HD fan boy but since we have it let's try to make it more functional.

AM radio's big problem is that it's not "new" or "cool". Sound quality is an excuse for a marketing problem (that, granted, has been in the making for a couple decades). I see young people all the time listening to the garbage built in iPod speaker thinking my $10 transistor AM radio I had when I was 13 sounded just like that (or better). Integrate the bands like I mentioned in my last post and people will incidentally scan to AM stations and discover programming they like. The increased chance of new/younger listeners will motivate AM owners to offer programming to them. Take it a step further and stop calling it AM - just call it radio. Since the public at large doesn't like AM, then stop using that term. They hit scan and end up on "Radio 1200" or whatever, they won't know the difference.

 

[Geographer]

After experience with IBOC over the past few years, I think there is some hope for the FM system - especially if asymetrical power levels are permitted, but the AM system as currently configured is not workable. A possible solution for the AM band would be to utilize the longwave band for the digital signal, while leaving the AM band for analog only. Instead of having the digital signal on band and on channel, perhaps there could be some information encoded on the analog signal in which the radio could lock onto the digital signal on the longwave band. With this system, to power level could be raised enough to provide a robust digital signal.

 

[w9wi]

BTW - I'm not trying to be an HD fan boy but since we have it let's try to make it more functional.

AM radio's big problem is that it's not "new" or "cool". Sound quality is an excuse for a marketing problem (that, granted, has been in the making for a couple decades). I see young people all the time listening to the garbage built in iPod speaker thinking my $10 transistor AM radio I had when I was 13 sounded just like that (or better). Integrate the bands like I mentioned in my last post and people will incidentally scan to AM stations and discover programming they like. The increased chance of new/younger listeners will motivate AM owners to offer programming to them. Take it a step further and stop calling it AM - just call it radio. Since the public at large doesn't like AM, then stop using that term. They hit scan and end up on "Radio 1200" or whatever, they won't know the difference.

I'm not a big HD fan either but this thread brings up some interesting ideas.

I don't think the "uncool factor" is AM's major problem though. Most stations simply don't have the signal to cover the entire market. Look in the ratings on this site -- while they're not the most valuable demos, in the Top 10 markets EVERY AM station in the top 10 positions is a 50,000-watt operation.

The idea of integrating AM radio and FM radio into, simply, "radio", is a good one. The stigma of "UHF" TV went away pretty quickly once digital tuning left absolutely no distinction between tuning channel 11 and channel 21. Handling that in software in radio would be trivial. (though it would still be obvious there's *something* different between "780" and "105.9")

Geographer: I don't think the navigation beacons are sufficiently cleared out of longwave to be able to reassign it for broadcasting. There certainly isn't enough room to give *every* existing AM station a digital assignment.

 

[Chuck]

A possible solution for the AM band would be to utilize the longwave band for the digital signal, while leaving the AM band for analog only.

I think you'd run out of space on the longwave band very quickly, at least if you planned to have room for all stations. Since Longwave is able to travel great distances, the interference issues might be very hard to overcome.

I agree that if we want a robust digital delivery system, the way it should be done is to put it on some frequency that is not occupied by analog signals. Too bad we didn't do that.

 

[DaveBayArea]

I agree that if we want a robust digital delivery system, the way it should be done is to put it on some frequency that is not occupied by analog signals. Too bad we didn't do that.

I don't know what the international shortwave rules are for the "tropical" shortwave bands (90 and 120 meters) but my amateur radio experience on 160 and 75 meters says that Digital Radio Mondiale transmitters on those bands could effectively serve a region. There's not a LOT of spectrum there (about 400 KHz) but you also have to consider the fact that only a few AM stations in a market are truly serious about going digital.

All of these ideas (longwave, modified HD, and tropical shortwave) have no real chance of implementation because we can't pay lots of $$ to Washington lobbyists. But it's nice to speculate.

Dave B.

 

[w9wi]

I don't think there'd be much competition for use of the tropical bands. (and if broadcasters came up with an alternate-frequency scheme that didn't occupy any more bandwidth than IBOC, I don't think the government would have any trouble approving it.)

Don't overestimate how much spectrum is available here. There are currently 117 channels assigned for AM broadcasting.

If the entire longwave spectrum, from 150-520KHz, were made available for broadcasting, that would constitute 37 channels. Four of them (440/450/460/470) would probably be unusable, since most AM radios have intermediate frequency amplifiers in that range. (if you had a radio with an IF of 450KHz, and a station broadcasting on 450, it is likely you would receive that station regardless of what frequency you actually dialed in on your radio)

There are a total of 70 channels in the tropical bands. Due to skywave, the necessary spacing between stations on the same frequency would be a LOT greater than what suffices in the current AM band, especially for nighttime operation. (but especially in winter, these frequencies can cover significant distances during the day as well)

It wouldn't take a whole lot of applicants to run out of room.

 

[pianoplayer88key]

As for expansion into longwave, I know the US generally uses 10 kHz steps on mediumwave. However, I'm thinking, since almost all radios that tune longwave (that I know of) tune in 9 kHz steps from 513 kHz down, how about using those steps there? You'd use 10 kHz to 520 kHz, then 9 kHz from 513 down to 153. (I might also be ok with extending it a bit lower than 153, but not all that many portable LW/MW/SW "general coverage" receivers that I'm aware of tune below 150 kHz.)

As for an upper extension, what about expanding continuously up to 3 MHz, at least on a partially shared basis? For example, in the 1800 to 2000 kHz amateur band, to placate the hams, power would be limited to 1 kW (or maybe 100 watts), channel spacing would be such that in local areas you might only have 2 or 3 strong stations (80-100 kHz spacing for example as opposed to the normal 40 kHz), a total of 5 or 6 stations receivable with a longwire antenna in the day, and nighttime spacing similar to the current separation between 50kW non-directional vs. 50kW directional stations in the current AM band.

Also what would be the effect on using other shortwave bands (especially in the 18 to 30 MHz range), as well as, say, expanding the FM broadcast band down to 64 MHz (some Tecsun radios will tune that low)?

 

[w9wi]

As for expansion into longwave, I know the US generally uses 10 kHz steps on mediumwave. However, I'm thinking, since almost all radios that tune longwave (that I know of) tune in 9 kHz steps from 513 kHz down, how about using those steps there? You'd use 10 kHz to 520 kHz, then 9 kHz from 513 down to 153. (I might also be ok with extending it a bit lower than 153, but not all that many portable LW/MW/SW "general coverage" receivers that I'm aware of tune below 150 kHz.)

That would buy us 42 channels instead of 37.

As for an upper extension, what about expanding continuously up to 3 MHz, at least on a partially shared basis? For example, in the 1800 to 2000 kHz amateur band, to placate the hams, power would be limited to 1 kW (or maybe 100 watts), channel spacing would be such that in local areas you might only have 2 or 3 strong stations (80-100 kHz spacing for example as opposed to the normal 40 kHz), a total of 5 or 6 stations receivable with a longwire antenna in the day, and nighttime spacing similar to the current separation between 50kW non-directional vs. 50kW directional stations in the current AM band.

Hams use receivers FAR more sensitive than consumer broadcast receivers. (and hams generally use "real" antennas -- the antennas in most consumer receivers are pretty poor) They also frequently use emission modes like Morse and PSK which work with VERY weak signals.

The amplifier for my ham station isn't working on the 1.8MHz band. So my power is limited to 100 watts. I have contacted all six continents with this station, and have little or no trouble contacting any place in North America.

Point being that placing even just one 100-watt BC station every 10KHz in the 1.8MHz band would make the band pretty much useless for amateur radio. (I mean, one station per channel *anywhere in the U.S.*. If you used 1810 in New York, Chicago, and LA it would be even worse.)

Sharing between broadcasting and amateurs doesn't work very well. (unfortunately, we're still having to live with it in 7200-7300KHz...)

Also what would be the effect on using other shortwave bands (especially in the 18 to 30 MHz range), as well as, say, expanding the FM broadcast band down to 64 MHz (some Tecsun radios will tune that low)?

Higher shortwave: you'd probably be limited to one or two stations nationally per channel. Otherwise the skywave interference would kill you.

FM expansion has been discussed quite a bit in other forums. It would have to be shared with TV, but it could work from a technical standpoint.

 

[stacker]

Long wave is not the way to go for HD. Think about bandwidth vs. time. At long wave, digital performance and throughput would be much worse than it is on the standard broadcast band. In addition, at the AM band and lower frequencies, digital pulses tend to "smear" due to propagation effects. An HD system needs to go up the band, not down.

 

[local oscillator]

These are all interesting fantasies, but the truth of the matter is that the Commission isn't about to allocate ANY additional spectrum to broadcasting. In fact, they are more than happy to grease the skids in our self-destruction of the spectrum we currently have.

IBOC? Sure! More IBOC power? No problem! Asymmetrical IBOC sidebands? You need only ask! LPFM? Sure thing, and we'll even eliminate third-adjacent protections and reduce second-adjacent protections -- how's that!?! Satellite-fed nationwide religious translator networks? Can do! Translators for HD side-channels? Why didn't we think of that!?! Get rid of the Table of Separations to make commercial FM more like AM and non-com FM? We'll get back to you after the holidays, but it shouldn't be a problem!

Now, guys . . . we've given you everything you've asked for, and you're still not happy? You know, maybe the internet is better. How about this: We take back all your spectrum, and y'all can stream on the web. No interference -- worldwide coverage -- what could be better? We knew you'd see the light. You're welcome.

 

[tomservo]

LO I agree with most of what you say, but the FCC is the height of hypocrisy when they don't allow little 100 watt LPFMs on certain adjacents but they make an exception for translators that run 2.5x the power.

I'm sorry, but I refuse to believe that an LPFM run by a non profit is a threat to a 100,000 watt station but a 250 translator relaying someone's computer in a closet (HD2) is not.

 

[KB1OKL]

There is entirely too much digital hash throughout the radio spectrum already, DRM causes just as much noise on shortwave as does IBOC on medium wave. I nightly pick up analog long wave European broadcast stations. One of long wave's pos points is that it can cover long distances by ground wave, IBOC or DRM would of course ruin that. Let's not curse them like the AM band has been cursed here in the US. The tropical band is called that for a reason, it is still used by many low power short wave stations in central America.

 

[local oscillator]

Zach, I agree completely with your point. My comments, however, were not made from a competitive viewpoint, only a technical one. We broadcasters, as an entire group, have been technically fouling our own nest, and we continue to do so with the FCC's able assistance.