RW Article: AM Radio Must Go All Digital

[pianoplayer88key]

13 miles? 5 miles? with 50 kW? (or was it 400 watts?)

I think we're going the wrong way here for efficiency of power vs distance!

I think amateur operators do a much better job at getting a signal out relatively far with relatively low power.

According to Rich Arland, K7YHA (now K7SZ), in World Radio magazine (Feb. 1990, year 19, issue 89, pp. 46-47) the long-distance low power record is held by KL7YU and W7BVV using one micro-watt over a distance of 1,650 mile 10-meter path between Alaska and Oregon in 1970. This is the equivalent of 1.6 billion miles per watt.

I also want to see better spectral efficiency. If I understand correctly according to Barry McLarnon's site, HD on AM does about 20 kbps in about 10 kHz of bandwidth. (I'm talking about the primary IBOC sidebands, 10-15 kHz removed from the carrier.) This isn't good enough for me.

For example, according to a Wikipedia article on spectral efficiency,

The modulation efficiency in bit/s is the gross bitrate (including any error-correcting code) divided by the bandwidth.

Example 1: A transmission technique using one kilohertz of bandwidth to transmit 1,000 bits per second has a modulation efficiency of 1 (bit/s)/Hz.

Example 2: A V.92 modem for the telephone network can transfer 56,000 bit/s downstream and 48,000 bit/s upstream over an analog telephone network. Due to filtering in the telephone exchange, the frequency range is limited to between 300 hertz and 3,400 hertz, corresponding to a bandwidth of 3,400 − 300 = 3,100 hertz. The spectral efficiency or modulation efficiency is 56,000/3,100 = 18.1 (bit/s)/Hz downstream, and 48,000/3,100 = 15.5 (bit/s)/Hz upstream.

With 18.1 bits/s/Hz efficiency, you could put 181 kbps in 10 kHz bandwidth. If that V.92 is full duplex, allowing simultaneous downstream and upstream in 3.1 kHz, then if I'm calculating/understanding correctly, it'd be 33.6 bits/s/Hz. This seems like it'd enable 336 kbps in 10 kHz.

Also the use of a good quality open-source codec would be desirable. I haven't done much study on this, but so far I like what I read about Vorbis. (I want to do some listening tests sometime so I can hear for myself what it's like with various parameters.)

Otherwise, if we can't BEAT the above for efficiency, I'd almost prefer to stay analog on AM. (Also, of course I'd want about as much copy protection as analog has.)

 

[JaneChristo]

I don't know what the future of AM is, but I'm having a hard time seeing it as HD.

Maybe not "HD"...but some other kind of "D" wouldn't you say?

 

[diymedia]

Oh, absolutely. Radio will someday be all digital, that's pretty much inevitable. But I think there are lots of other options and paths to explore, some of which might not even include the traditional AM and FM bands.

 

[JaneChristo]

Oh, absolutely. Radio will someday be all digital, that's pretty much inevitable. .

You'd never know if reading here. Most of the anti-HD writers seem to want to go back to a day of AM only....with clear channel station wavering and fluttering and reaching half the country. ;-)

 

[Carmine5]

You'd never know if reading here. Most of the anti-HD writers seem to want to go back to a day of AM only....with clear channel station wavering and fluttering and reaching half the country. ;-)

It's not so much a case of being against digital, Jane, as it is being against iBqiuity and its business model as well as hybrid digital; sending analog and digital over the same carrier with the resultant sideband splatter (a problem iBiquity chooses to ignore, play down or otherwise not deal with). Many here are proponents of DRM and DRM+ which is an open digital standard.

If the day ever came when the FCC announced a sunset for analog radio and threw out iBiquity's HD Radio in favor of DRM, I think we would see more strong, enthusiastic support for digital here.

 

[iyiyi]

It's not so much a case of being against digital, Jane, as it is being against iBqiuity and its business model as well as hybrid digital; sending analog and digital over the same carrier with the resultant sideband splatter (a problem iBiquity chooses to ignore, play down or otherwise not deal with). Many here are proponents of DRM and DRM+ which is an open digital standard.

If the day ever came when the FCC announced a sunset for analog radio and threw out iBiquity's HD Radio in favor of DRM, I think we would see more strong, enthusiastic support for digital here.

Some pretty amazing electronics is this HD technology. An AM or FM analog signal simultaneously broadcasting on the exact same frequency as // digital HD1. FM has the added HDs capable of simultaneously broadcasting an analog // HD1 plus 3 more HDs, each with it's own separate programming.

I can't think of another non military or non aerospace radio system on earth that has all of these options!

-

 

[diymedia]

So amazing, in fact, that stations are adopting it like hotcakes, there's tons of listening devices in the marketplace, and listeners sing its praises every moment. And this is only the "halfway" implementation!

 

[TheBigA]

Keep in mind that there hasn't been much growth on the AM/FM side either. Especially AM. No one's rushing out to buy the latest FM radio either. All the growth for OTA radio is in streaming. The bad news there is the cost. But people are willing to pay what it costs to listen to FM on their phones or other devices. Radio IS going digital, using a less efficient system, regardless of what anyone thinks.

 

[diymedia]

If the day ever came when the FCC announced a sunset for analog radio and threw out iBiquity's HD Radio in favor of DRM, I think we would see more strong, enthusiastic support for digital here.

This is definitely something to raise in the upcoming "AM revitalization" NPRM. It's not like it's impossible: Nautel makes "trimode" AM transmitters (analog, HD, and DRM), some of which are probably already in the field. Since both are all-digital tests, there's no spectrum-funniness to worry about, like there was with the NRSC's attempt to comparatively test Eureka 147 back in the day.

BTW, I don't see formal NRSC engagement with the all-digital AM tests conducted over the last year. Will it be pulled in to help with industry-endorsement toward a mandate, or will it be bypassed like the FM-HD power hike was?

 

[TheBigA]

BTW, I don't see formal NRSC engagement with the all-digital AM tests conducted over the last year. Will it be pulled in to help with industry-endorsement toward a mandate, or will it be bypassed like the FM-HD power hike was?

I don't see the FCC devoting any spectrum space for OTA commercial radio. And I don't see anyone in the industry pushing for a mandate. It's definitely not coming from anyone in the electronics industry. They've given up on AM & FM.

From where I sit, the radio industry has moved on to streaming. That's where their investment and attention is. In a few years, AM will be like CB, as the industry abandons it completely as industry abandoned cities like Camden and Detroit.