Radio reception now vs back then

[TheBigA]

Unfortunately, it looks now like it may not 'save' AM, although maybe 15 or 20 years from now the remaining AM stations may be all digital.

My view is the main problems AM has could be solved by some form of digital signal. Unfortunately IBOC isn't the best solution. I think the best solution is a variation on IBOC that may never come to pass because the cost of creation and marketing exceeds the potential revenues such a technology could provide. The catch is it needs to be able to improve AM audio quality without requiring the entire world to replace its existing radios. I'm the last idealist who thinks it could be done. Just not sure how.

 

[MarioMania]

When did the FCC force AM's to go 5 kHz of Audio?

 

[davideduardo]

When did the FCC force AM's to go 5 kHz of Audio?

Never.

However, stations that did AM HD need to reduce the analog audio to 5 to 6 kHz to accommodate the digital sideband signal.

 

[MarioMania]

Oh ok, thanks David..

So it just the receivers that sound bad

 

[rbrucecarter5]

Unfortunately, it looks now like it may not 'save' AM, although maybe 15 or 20 years from now the remaining AM stations may be all digital.

To look at the future of AM, you have to look at the previous 15 to 20 years for trends. I see even more foreign language, less music, more interference from even more electronic devices. AM listening over the internet with the over the air signal maintained just because there are hundreds of millions of legacy radios in the hands of consumers, and it will take many more decades for all those radios to slowly be retired and gather dust in attics, basements, and flea markets.

If there will be a new "trend" I think it will be information. The band is ideal for speech, and thanks to dashboard radios there is an audience. Drive to Florida - there are already AM stations that do nothing but advertise Orlando attractions. Drive to Las Vegas, the only FM stations you can receive on some highways are running continual Vegas promotions and occasional weather information. DFW's airport station - almost a must when you are driving to the airport. Small isolated subdivisions operating AM stations, there are probably 3 or 4. So if there is a trend - I think it would be more and more infomercial / traveler information / single purpose AMs. Listen to get what you need, then back to satellite or FM.

I just don't see digital AM changing anything - the laws of Physics are constant, and ever increasing interference levels will stop digital lock as effectively as they put a loud buzz on analog. Interference is interference, and one this is abundantly clear - digital AM is very subject to drops from interference. It just doesn't work in the presence of interference. With analog, you might get some audio leaking through if you null the interference, drive down the road, or otherwise re-position the radio. You can hear the interference decrease.

Digital? I think not. People don't buy radios as it is - radio is a box sitting in the corner that seldom gets used, maybe people wake up to music on a clock radio. Maybe they tune in for game. Spend 50 or 100 for a new radio to get digital stations? Dream on. It hasn't happened for FM and it darn sure won't happen for AM. Digital was a solution for a problem that didn't exist, and the implementation is poor and unreliable. Nobody will pay for an Edsel and that that is what HD is all around.

 

[1L6E6VHF]

Oh ok, thanks David..

So it just the receivers that sound bad

Basically, yes.

For several decades (since the end of the crystal set era), most AM receivers have failed to pass the whole audio frequency range transmitted by the broadcasters.

When designing an AM broadcast receiver, a trade-off needs to be made between frequency response and selectivity. A broadband circuit would carry all of the brilliance of the original broadcast, but any degree of adjacent-channel interference would be carried to the detector as well, causing an annoying whistle from the adjacent stations' carriers and splatter from their sidebands.

Using a narrowband IF chain blocks the adjacent channels, allowing one to hear the desired station at a greater distance, but then the bells and cymbals will be thrown into the trash with the interference.

There were ways around the paradox. A few receivers had a selectivity switch - wide for music and narrow for dealing with noise and interference, but by the time manufacturing had become cheap enough to justify its inclusion, the industry had decided that "AM was for talk".

A notch filter could cut the whistle (the most annoying part), but not the splatter. A standardized noise reduction system could have reduced the splatter, but that would have meant standardized processing - unthinkable in an era when several competing companies were in the business of selling stations a new processor every other year.

An unfortunate problem was the choice of 10kHz (or 9kHz) channel spacing. A 10kHz whistle is very effective at getting through the human ear canal (resonant at about 10kHz) to the eardrum (a "shrill" sensation). Had they chosen 12.5kHz (86 channels not including X-band) or 13kHz (83 channels), there would have been far less interference, especially on local and clear channels (fewer channels, but more service).

As for "when did the FCC force AMs to go to 5kHz of audio" - you may be thinking of the NRSC standard, announced about 1985, introduced about 1987, supposedly "voluntary with a five-year sunset", only to be abruptly made mandatory when not enough stations joined voluntarily (about 1989). It enforced a 10kHz cap (not 5kHz). The cap had been 15kHz.

 

[boombox4]

One problem with mentioning of receivers here on RD is many people here on this forum are DXers who use digital SW receivers, which are famous for having midrangy, 'communications' style audio -- which sounds awful on the tinny speakers and more or less mediocre through headphones. I have several of these digital SW portables (mostly SAngeans) -- great for DXing, not so great for pleasant listening.

You can't listen to AM on your average digital SW portable and expect it to sound great.

There are some AM portable radios that sound OK. GE Superadios being one model. They work with the same 10 khz spacing that your Sangean SW radios and Grundig SW radios do, but the bandwidth is around 7-8 khz (?) or so and the audio circuit at least sounds more tailored for pleasant listening.

I keep reading about car radios AM sections sounding like junk. The one in my late 80's model car blew out soon after I bought it (drive train works great -- that's enough for me). So I really don't know about that. But I'll take their word on it. When the radio in my car worked the AM section sounded pretty muddy.

 

[rbrucecarter5]

One problem with mentioning of receivers here on RD is many people here on this forum are DXers who use digital SW receivers, which are famous for having midrangy, 'communications' style audio -- which sounds awful on the tinny speakers and more or less mediocre through headphones. I have several of these digital SW portables (mostly SAngeans) -- great for DXing, not so great for pleasant listening.

You can't listen to AM on your average digital SW portable and expect it to sound great.

There are some AM portable radios that sound OK. GE Superadios being one model. They work with the same 10 khz spacing that your Sangean SW radios and Grundig SW radios do, but the bandwidth is around 7-8 khz (?) or so and the audio circuit at least sounds more tailored for pleasant listening.

I keep reading about car radios AM sections sounding like junk. The one in my late 80's model car blew out soon after I bought it (drive train works great -- that's enough for me). So I really don't know about that. But I'll take their word on it. When the radio in my car worked the AM section sounded pretty muddy.

The highly sensitive AM section in my Pioneer aftermarket radio sounds great, but is prone to clipping. I suspect that is because it is done in a DSP algorithm.

Other than car radios and the aforementioned shortwave portables - ALL AM sections today have wideband IF. Any frequency limitation is only due to an RC low pass filter on the audio. That does NOT stop things like adjacent channels and HD buzz. It only attenuates them in the audio domain.

Some of the Delcos made right after the switch to ceramic filters on FM had very broad IF sections, as much as +/- 600 kHz. Driving in fringe areas with lots of first adjacents sounded a bit like a super skip event with two or more stations mixing together. Changing the IF filters to 150 kHz made them into really good radios. What does that have to do with AM? The cheap ceramic filters now in use do the exact same thing. In areas crowded with stations, you can pick up two or three and they mix together. Regardless of the audio response. BAD radios - BAD design. But - cheap and good enough for strong locals. Pull out the low pass filter, they sound great on music. If there are no adjacents mixing in.

 

[kenglish]

I'm noticing more interference on FM due to new gadgets and electrical things. There are traffic lights in my neighbourhood that make some of the weaker FM stations impossible to listen to. The flashing don't walk signs create a hash that blows the stations right off the dial when they are on, but when they flash off the station pops back in. When they're solid, forget about it. This affects at least 4 local FM stations in Ottawa. Some computers and electronic gadgets also cause FM interference. In my Office, FM radio is impossible on all but 2 stations, and that's only because their towers are 5 blocks away. AM is fine on the locals and even 3 out of towners from Montreal make it in At night if you can hear it half decently the signal gets in. The only problem on AM in the office is if the receiver is too close to a monitor.

You should complain to the city traffic engineering department, and have them try some sort of filters on those lights. If they are causing interference, it's their job to fix it. Make them find a fix, and apply it to all their lights.

 

[gr8oldies]

I don't have any technical details, but observations. All else being constant, daytime reception where I grew up in West Central Ohio is about what it was in the 70s. The difference is at sunset and night with more frequencies being "graveyard", more stations on at night (including flea power) and more Latin American interference. Those midday winter skip events and auroral nights and mornings can still be fun. In East Tennessee where I live now, it's harder to find an electrically-quiet place to listen for DX. I guess the National Park is next. On FM, the difference was, particularly if you didn't live in an urban area, more stations that signed off between 10pm and 1am. Some of the others had lower power and smaller towers than they do now. Even a non-DX radio could get a lot of Detroit and lower Michigan/SW Ontario stations in the wee hours from Western Ohio.

 

[cyberdad]

@gr8oldies: Well stated.