Digital Signals Spark Static From AM Radio

Carl Bialik writes "Digital radio is touted as broadcast radio's golden ticket, but the transition to digital broadcasts is creating static and interference for many smaller AM stations that are still analog-only, the Wall Street Journal reports: 'The AM stations most affected are those whose neighboring stations -- nearby on the dial -- add a digital signal.' The WSJ adds, 'For some small AM operators, it adds insult to injury that the only company licensing the digital broadcast technology is one backed by the small stations' deep-pocketed competitors.' Critics question why the FCC only approved the technology from that big radio-backed company, Ibiquity."

Money money money...

"Critics question why the FCC only approved the technology from that big radio-backed company, Ibiquity."

Silly critics. I don't think there's any question at all.

Ibiquitous static

The AM stations most affected are those whose neighboring stations -- nearby on the dial -- add a digital signal...Critics question why the FCC only approved the technology from that big radio-backed company, Ibiquity.

Man, that Ibiquity seems to be all over the place these days.

Critics question why

Critics question why the FCC only approved the technology from that big radio-backed company, Ibiquity.
What about: 'Because they payed the most money and the FCC does not mind creating monopolies when properly greased.'

Once again, I am happy not to live over there, my middle of the road ideas would be considered ultra left wing in over there.

Just like HDTV

Can someone explain why I need to by a $300 radio to listen to something that is not perceptibly different?

At any rate it seems like another way to fleece the public.

Anyway analog broadcasting should be preserved as they are easy to implment and use in the event of an emergency.

Don't have the time

to listen to AM radio, usually the morning shows are the Howard Sterns & I'm rushing to get to work. Now PM radio tends to be more informative.

Sounds like my DVD remote also operating my old TV

My TV was so old that when I added a DVD player, the power button on the DVD remote also sent an "8" signal to the TV, thereby changing the channel. The company that made the TV had already been out of business for at least 10 years when I got the DVD player. I guess they never anticipated someone would have a clash of technologies more than two decades apart.

Oddly enough, I have one of those "emergency" flashlights that would also change the channels on yet another ancient TV.

And in yet another case, we had an ancient answering machine that would randomly pick up other people's conversations for seemingly no reason. Technologies clash more often than we realize.

Tough call for some of you

This will be a tough call for some of you. Lots of small AM radio stations are Christian stations. Prejudice against big business or prejudice against religion -- which prejudice will win?

bad protocal?

Interesting article but it doesn't really establish a cause and effect for the interference. Wonder if this is this is caused by a limit in the digital protocol, a design problem with the transmitters, or if the problem can be solved by improvements in receivers?

Modulation Theory 101

I design radio test equipment for a living - so welcome to Modulation Theory 101.

Amplitude modulation, or more correctly double-sideband non-suppressed carrier amplitude modulation (FCC emission type A3E), results in an RF spectrum that is twice as wide as the highest frequency component of the modulating signal. In other words, if the signal you are modulating has as its highest frequency component 3kHz (normal voice signals), then the resulting AM signal will occupy 6 kHz of RF spectrum - from 3kHz below the nominal carrier frequency to 3 kHz above the nominal carrier.

Now, we have to consider the concept of "receiver bandwidth". A properly designed radio receiver will only pick up signals within a given frequency difference of where it is tuned (the "tuned frequency" or TF) - this is the receiver bandwidth (sometimes referred to as "IF bandwidth" since in modern superheterodyne receivers it is the bandwidth of the narrowest intermediate frequency section that determines the overall receiver bandwidth).

Now, consider the case of 2 radio stations spaced such that their carriers are 10 kHz apart - the normal spacing for AM radio stations. Assume your radio is tuned to one of the stations. If your radio has a receiver bandwidth of 20 kHz (in other words receiving signals from 10 kHz below tuned frequency to 10 kHz above tuned frequency), you would hear the station you *weren't* tuned to as a 10 kHz whine on your radio (the carrier of the other station, 10 kHz off your tuned frequency), plus the audio of the other station inverted in frequency (low tones become high tones and vise versa).

So, your radio has to have a narrow filter to receive only those signals within 5 kHz of tuned frequency (total 10 kHz). Now, a perfect "brick wall" filter would allow, say, 4 kHz through, but stop 4.00001 kHz dead. Now, filters are not perfect, and so if your filter allows signals from, say, 4 kHz away from TF, then it will not totally block signals until they are, say, 6 kHz from TF. So, radios are designed to allow signals +/- 3kHz from TF in (receiver bandwidth of 6kHz), and block signals more than 5 kHz from TF.

OK, now, how do we add any new signals to the A3E signal so that we can put the digital signal in place? We cannot place those signals within 3kHz of the carrier without going to a LOT of trouble, otherwise analog radios will "hear" the digital signal as noise. So what IBOC does is exploit that "no man's land" from 3kHz away from carrier to 5kHz away from carrier to put the digital signal in. Now, your old analog radio will still "hear" these signals to an extent, but between the attenuation of the receiver bandwidth and the attenuation of the audio chain, this noise will not be very perceptible.

HOWEVER - remember how I said there were no perfect "brick wall" filters? Well, that applies to transmitters too. The transmitter may be putting signal into the 3 kHz to 5 kHz region, but it will put some unwanted signals beyond 5kHz (they will just be very weak compared to the desired signals) - and that means into the frequency band of the next guy on the dial. However, if the next guy is far enough away in space, your signals that are in his band (which are already weak) will be weakened further by distance, and won't be perceptible by the other guy's listeners. Also, your signals that are in the 3kHz to 5kHz area will be weakened by distance, and attenuated by the receiver's filters, and so they, too, won't be very objectionable.

Except in the fringes between where your spatial region stops and his starts. That's what is happening here - if you are close to "the other guy" you won't hear the interference, but if you are far from him, and close to the digital station - you get noise where there was none before.

Add to this the fact that the stations that are going digital are the stations with money - and how do you get money? By having lots of listeners. How do you get lots of listeners? Among other things, by having lots of POWER <Tim Allen Grunt>. The little station

New method for earning money as Clear Channel

A simple 4 step process:
1. Buy radio station neighbouring a competitor's band.
2. Broadcast FCC legal digital interference.
3. ???
4. Profit!

Major lawsuits coming? Anyone?

Digital AM quality issues...

I recently purchased a car stereo with digital support and can say that the AM digital stuff sounds absolutely terrible! You really hear the digital artifacts... tinny, cellphone-ish sounds. Also, the analog signals aren't in sync with the digital ones so that when the stereo goes from one to the other, you either miss something, or hear the same thing over again... typically around 4 seconds worth. Get into an area where the AM signal isn't too great, and the stereo repeately goes back and forth between analog to digital. It's enough to drive you insane.

Hopefully digital AM will get dropped as people realize how terrible it sounds.

FM, on the other hand, sounds great and doesn't have the sync problem.

If I can only figure out how to turn off the digital AM support in my stereo!!!

In case this is just a fluke, here are the details:
AM 740 in San Francisco.
Headunit: Kenwood KDC-890
Digital Box: Kenwood KTC-HR100

What "digital" radio is...and why it's bad

I am a broadcast engineer.

This "HD Radio" is actually called IBOC (in-band, on-channel). Radio works by changing the amplitude (AM) or the frequency (FM). You're only permitted to change it by a certain amount--your bandwidth--otherwise it will interfere with adjacent stations. By adding more information, the digital data stream, you're using increased bandwidth.

The other big issue with AM is overnight. Most AMs power down or sign off at sunset because the atomosphere changes overnight and AM travels much farther--for example, I get ESPN 1000 out of Chicago 1,200 miles away and the 1000khz station here shuts off overnight. The sky is already being polluted with IBOC hiss (sound just like a modem) and it's DEFINITELY hurting the smaller AM stations who have special authorizations to stay on overnight, but at a significantly reduced power.

Surf the spectrum and you'll see. This has been a HUGE issue in the broadcasting community and it's about time it gets mainstream attention.

AM band

I really do not see the issue here, AM should have been killed off 20 years, sounded like ass then, Sounds like ass now, all i can see is a few of those Religous stations are mad because they are trying to reclaim those frequencies for hopefully something useful. Yes i realize AM was the FIRST sucessful broadcast radio technology with that said, put an exhibit in the smithsonian and call it done.

Ibiquity vs DRM - Digital Radio Mondiale

I love it, another untested closed standard.

The AM MW mode should be left alone. The band that it is used in the US is not that reliable for digital modes, but it is very reliable for AM transmision to local areas.

This band/mode is essential for emergencies. Everyone in the US has an "AM" radio somewhere in the house or their car. It will just work.

Has the FCC rated this HD radio as an actual mode?

I have started to experiment with drm on my HF equipment and in fact i am upgrading to a SDR-1000 in a month or so.

With my existing equipment, I have heard a few of the DRM broadcasts on HF Shortwave and they are impressive. I have heard that you can broadcast it with a SDR-1000.

DRM is an open standard based on mpeg4. In fact this is the standard for european countries. There is GPL code for both listening and transmitting it.

http://en.wikipedia.org/wiki/Digital_Radio_Mondial e [wikipedia.org]

KB0FHF

HD Radio is great

Digital radio sounds MUCH better then the old AM and FM. And the bit rate is also much higher than the Satellite providers XM and Sirius. It is CD quality audio on most stations.

So I can see why the radio stations, large and small, are rushing to push a free service that sounds much better than anything out there.

Most HD stations are still without commercials!! And from what I hear, they should be that way for at least the next year or two.

By the way, doesn't Ibiquity have a patent on the HD technology?

AM Radio Interference

AM radio sucks up interference easily. When I want to listen to sports radio instead of the iPod, I can tell every time someone within 10 feet of me gets a text message or call. It's a nice discreet REAACHACHAHHEHRTAHAHHAHAHACHHCHCCCT noise.

Ethernet interferes with AM 560 kHz

Ethernet interferes with AM 560 kHz - I can vouch for that. My dad listens to AM 560, and started getting interference with it when their computer was hooked up to a cable modem. I did all sorts of troubleshooting to isolate the problem, and got it down to an Ethernet cable from the modem to the network card. I looked for, but couldn't find, a shielded cable with RJ-45 connectors. (If anyone knows of one - let me know!) I ended up connecting to it via USB instead, which took care of the problem.

I'll bide my time...

"Can someone explain why I need to by a $300 radio to listen to something that is not perceptibly different? At any rate it seems like another way to fleece the public." I totally agree. Until sometime as I NEED a digital radio (ie, when/if AM stations are slowly phased out), I think I'll stick to a regular radio receiver. The supposed increase in quality is negligible, and in my opinion, definitely not worth the money. I'll hold out for as long as I can.

I thought broadcast radio......

Would be saved by turning into what satellite radio already is. Until they cut the commercials, stop censoring music, and get some variety they will continue to watch their audience get smaller.

Ah, those Yankees

It's worth noting that the "digital" radio referred to is the In Band On Channel (IBOC) system used only by the U.S., and manufactured by Ibiquity.

The rest of the planet wisely chose a system that was entirely digital, and which consequently does not have these problems, while the Americans, defending the inalienable right to own radio stations using 1930s technology, or some such thing, fought for a system which sqeezes a digital audio stream into their existing AM or FM signals.

An all round bad idea, and yet another demonstration why engineering decisions shouldn't be the province of politicians and lobbyists.

Blah blah.. politics and big money... blah blah...

FM is also affected by IBOC interference

In particular, it causes neighboring FM stations to disappear if they are lower-powered or further away (a common experience when listening in the car). For example, when 107.7 in San Francisco turned on IBOC, it made 107.5 from Santa Cruz (the famous KPIG) disappear from the south bay.

In my experience, it also degrades the analog FM signal (of the IBOC broadcaster) with additional multipath.

It's sad that the FCC will go after 2 watt pirate broadcasters, but not care about interference on a much larger scale. And, as mentioned elsewhere, the codec is proprietary, and widely considered to sound like crap.

Same reason

For the same reason that the FCC keeps certifying cell phones, CD players, and laptops that interfere with planes [slashdot.org]. Clearly the FCC cares more about corporate profits than their stated mandate of preventing interference in the radio spectrum.

Heads need to roll at the FCC, they are not doing their job.

-- Bob

Monopoly

A guy working at a radio station once told me that the large networks pretty much own the market. It used to be small independent radio stations, but not anymore. Like record labels. There are some small ones, but they occupy such a small marketshare that they are almost neligable.

What's the Point?

I'm not sure why any of the broadcast stations are bothering with it. If they really cared about audio quality, they wouldn't have an Optimod cranked up to 11 in their audio chain. Most people wouldn't believe how good a properly run AM or FM station can sound, they've never heard one.

Computer and entertainment devices are much worse

IThe worst source of noise in the AM, FM, VHF, and UHF spectrum comes from the poorly designed and shielded switching power supplies that are now almost universally used. I use the HF spectrum for communication, and my power supply for my laptop wipes it out. It even interferes with my TV. I know its the supply as I am an electrical engineer who has done some design work for these types of power supplies. Plus, as soon as I turn off the supply, the interference goes away. Unfortunately, it is very hard to filter and shield power supply noise without creating a very bulkiy power supply. It is not quite as bad for entertainment components as there is more space for the needed circuitry. But laptop power supplies can only be so big before they are unwieldy.

The large cylindrical objects that are part of computer power supply cables are attempts at filtering the noise, but they really only work for very high frequencies. Plus, ethernet cables and the AC line cord also contribute to the problem.

Another potential huge source of noise is the BPL internet access networks that radiate RF energy like a huge antenna because the power lines on the poles act like huge antennas.

I think it is only going to get worse. All of these devices have to meet FCC requirements for emitted radiation, but they really can't go too far without drastically increasing the cost of power supplies. I guess for now, there really isn't a good solution to the whole problem.

The question is...

The real question is - why is it only in the US that these odd technology hacks are being used - the rest of the world is using DAB for digital broacast radio. It seems like the US is the only place that WON'T be using DAB.

You want to know why the FCC blessed one method?

All you have to do is look at the AM stereo fiasco [wikipedia.org].

uh, standardization...

You know, the slashdot uproar when industries fail to standardize is matched only by the uproar when they do standardize. Why did they only approve one? The stakeholders (manufacturers, stations, govenment) got together and made a decision to go with an established technology. The last thing we needed was a radio format war.

What happend to good filter design ?

1.Design of a good SELECTIVE output filter for D.R. amplifier is very expensive.
2. LINEAR hf high power amplifier - same

it's nothing wrong with technology ..but if you want to get it cheap with long range...

They all just want money !!

Bit rates for digital radio...

FM: 96K bit

AM: 32K bit

They use a codec similar to AAC.

Re:Boo Hoo Hoo.

Not everyone wants to shell out money to upgrade their car radio to satellite. Out here in Sask. AM stations rule because of our vast geographical distances. The AM dial is not crowded, and some nights you can pick up stations that are more than 400 miles away.

I wonder though, is this digital signal the stuff that identifies a radio station for new car radio displays?

Re:Maybe this is a wakeup call...

And for those who are going to say "silly, AM isn't hi-fi," just listen to a GE Super Radio or Tivoli sometime.

Also worth including on that list is the cc radio [amazon.com]. I've had very good luck with mine, going on about 4 years now. The digital tuning is a godsend and I can pick up distant (aka our local) TV audio quite clearly, even thought the video is unwatchable on a regular TV antenna.

I didn't know about the SuperRadio [radioshack.com] before but I'll go check one at at Radio Shack (hopefully they still have radios on display behind the cell phones and batteries).

Also, a good AM Antenna makes a world of distance. I used to have this passive AM antenna that was advertised as designed for folks in Alaska to pull in stateside AM. It really helped pull in a signal, but I haven't been able to find a replacement since it was stolen at college. It was about a foot round with a big dial on the face. Anybody know what they are?

Everything interferes with AM

If someone set up a big cat stroking parlour down the road that would cause static too! It has been known since forever that AM is bottom of the shitpile in the RF fiefdom. That newer broadcasting methods and more packed airewaves will hit AM is obvious and rather than moaning should thank their lucky stars tat they have been able to continue so long.

Still, I enjoy fiddling with crystal radios etc and would hate to see the AM stations lost completely.

Re:Digital or Digital?

No, as I understand it the US's digital audio broadcasting system works differently to the UK's. In our case DAB multiplexes are broadcast in an entirely seperate band to analogue radio (I think DAB uses Band III, used for ITV on the old 405 line VHF TV system that closed in the mid-80's). As I understand it US digital radio is broadcast in the same bands as analogue AM radio, and they're piggybacked onto existing channels, and increase the bandwidth they use, squeezing out stations.

It can't be RDS, as RDS is only for FM radio, and we're talking about AM.