Paul Litwinovich on “The Life, Decline and Possible Rebirth of AM”

Zenith-Shuttle-DialMany thanks to the SWLing Post reader who noted this latest post by Paul Litwinovich at WSHU (Paul is frequently referenced here on the Post).

A short excerpt:

“AM occurs elsewhere in nature. A lightning strike or manmade electrical discharge will produce a burst of electrical noise that varies in amplitude. Since AM radios are designed to detect variations in amplitude, this is why they are prone to interference from such things. AM held sway as the primary method of modulating a radio wave up to WWII, not only for broadcasting, but for all types of radio communications.

Every vintage consumer radio, be it standard broadcast or shortwave, up to WWII, received amplitude modulated signals. Nowadays, AM broadcast stations are associated with lower quality audio, but such was not always the case. Receiver design really came of age in the 1930s with the superheterodyne circuit and advancements in loudspeaker design. The grand floor consoles of the late 1930s leading up to WWII were capable of producing audio that was very good, even by today’s standards, the only exception being that they were monaural, as stereo technology was still a ways off.”[…]

Litwinovich’s article is a must-read as he gives a concise overview of amplitude modulation, AM vs. FM, and even covers current proposed uses of the broadcast band (something we’ve also recently mentioned).

Click here to read The Life, Decline and Possible Rebirth of AM.

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8 thoughts on “Paul Litwinovich on “The Life, Decline and Possible Rebirth of AM”

  1. Robert

    The “Internet Revolution” was a marketing fad that is now long gone.

    The so-called revolution to bring equality, freedom of speech and the free exchange of ideas has fast turned into a medium of censorship, regulation, propaganda and excess commercialism. It has in essence been corrupted by human greed and stupidity. The internet of the 1980’s -1990’s was actually a more intelligent and creative place to be than the mess of garbage it has become today.

    Sure, there are good quality resources on the net (like this site) but they are fast becoming rare and heavily neutralized to suit the views of vested interests.

    I see a revival of all things radio in the near future as people start to get back to basics and search for content that is not filtered and regulated in some way. Shortwave could be at the forefront of this. Oh and AM radio still rocks – a 9kHz BW clean AM signal is just glorious to listen to.

    Reply
    1. DL4NO

      Please do not give the impression that commercial radio is or has been any better than the Internet today: For most of their history, broadcasters in general and international broadcasters especially where either commercial companies oder state-owned entities.

      My most important point is the loss of connectivity when desaster strucks. Here in central and northern Europe hardly any AM transmitters are still working. We rely on FM or DAB stations that can be heard for 50-100 km. Here in Germany they should have kept at least the longwave transmitters of Deutschlandfunk. Three transmitters had been enough to cover all of Germany.

      In the US with the weak infrastructure in many parts of your country you experience these problems from time to time. Here in Germany this hardly ever happens which reduces the awareness for this possibility. For example hardly anyone has any form of emergency power supply because electricity is typically lost for perhaps 15 min a year.

      Reply
  2. Steven Crawford

    I just can’t agree with this:

    “Get rid of the 50 and 100 kW clear channel stations. Originally they were needed to reach deep into rural America where no other service existed. Now many are run like local stations. Someone 200 miles away does not need to hear traffic and weather reports for the city that these stations could serve well with 10 kW.”

    With family evacuated and scattered across the state following Hurricanes Rita and Ike the clear channels, WBAP, KRLD, and WOAI, near them were useful to me in keeping tabs on events and circumstances that may affect them. Following Hurricane Katrina, WWL was helpful in preparing for the spillover aftermath that was headed our way. Every one of those stations is more than 200 miles away as the crow flies.

    I’ve noticed the few local stations that are able to remain on air, such as KLVI and KTRH, following an event rightfully are so focused on what is happening in their immediate area and providing news and solutions as they occur in their area perspective in the “bigger” picture is lost. Again the clear channels have proven their worth in giving insight to other affected areas.

    I’ve been in situations where any combination and all combinations of broadcast FM, landline, cell, VOIP, cable and televised communications have been out but a clear channel AM broadcast has always been available at night and with luck during the day as well.

    Reply
  3. ¾ Blind

    If I could wave a magic wand I would have manufacturers of upscale AM radios incorporate AMAX receiver specifications for AM bandwidth, distortion, de-emphasis, everything save for AM stereo. I say AMAX not because it is the best standard, but because it is an existing and documented standard. One would think with DSP such design should be doable at minimal cost. I would also ask broadcasters to reduce audio compression at all stages in the signal path from studio to transmitter. Radio is first and foremost all about the pleasurable listening experience. Convenience and low cost are secondary.

    Reply
  4. DL4NO

    FM signals need not be 200 kHz wide.

    The original FM system used +/- 75 kHz frequency shift. With a 15 kHz upper modulation frequency this led to a “modulation index” of 5, i.e. 75 kHz / 15 kHz. The advantage of such a high modulation index is noise suppression.

    A FM stereo signal uses a spectrum up to 53 kHz, reducing the modulation index to 1.4. This is why a stereo signal from a weak station brings so much noise so you press the mono button.

    A FM signal has a minimal bandwidth of 2 * modulation frequency + maximum frequency shift. To this you should add 1-2 “higher-order sidebands”, especially at the receiver side. Receiving these sidebands greatly improves the sound fidelity. But the energy contents of these sidebands diminishes quickly and need not interfer with other signals.

    If you reduce the frequency shift you lese some S/N ratio but you still have the other advantages of FM modulation. Ham radio went this way: At least here in Europe we started with a 50 kHz grid when the commerical services went to 25 kHz and we got their old equipment quite cheaply. Including some frequency instability we could do +/- 15 kHz or so. These days we use a 12.5 kHz grid and +/- 2.5 kHz frequency diviation. That cost us quite some S/N ratio but allowed many more repeaters to get online.

    Back to broadcasting: With a relatively low deviation of perhaps +/- 2 kHz a channel width of 15 kHz could be enough. You would win quite some noise suppression and less interference from other stations.

    But all that is 80 years old technology. Today a new system would go digital. But in my view DRM has long gone down the drain. Whata pity!

    Reply
  5. David

    As much as I love AM radio and have tons of memories of listening to local and distant stations for decades, his article has some issues.

    First, no comment about the Internet revolution. This is not a small oversight. 20 years ago if the only local oldies station was on a scratchy AM station you endured it. Now you go to Pandora. If you wanted to hear if your school was open after a snowstorm you turned on the AM station. Now you go to the school’s website. Weather? On your phone. Political commentary? To the blogs.

    Second, no comment about the night time coverage problems. The only AM station in your town, but Chicago’s Clear Channel is 500 miles away? Too bad, you have to go down to an unusable power — or just shut down completely. In 2016 some stations are still expected to break even at a laughable 10 watts after dark — which kills their winter listening. We worry about losing the tradition of clear channels, but small town radio would love to be able to hear their own station in town at 6pm in December.

    Third, IBOC has been a total disaster. It is not doing well on FM, it’s barely alive. Radios were overpriced, the signal sucked, the audio quality sucked, and the programming was a joke. 10 years since I first heard HD Radio I know no one outside of industry friends who wanted one. Truth is, AM HD is a non-issue outside of a few hobbyists, both pro and con.

    Fourth, people prefer music on FM and it’s been that way long before any regulation changed things. You can go back to the late 70s when Top 40 began migrating en mass to the signals. AM Stereo tired (and it actually did sound pretty good), but little happened.

    I’m not saying AM is dead, or that it needs to die. But longing for the past and blaming the FCC isn’t going to cut it. Frankly some stations need to go dark in major cities — or there needs to be a time of experimenting with open digital formats that might give consumers a reason to go back to AM. HD Radio failed, I’d love to see DRM given a chance on a few frequencies as an experiment. I’d love to see some people attempt formats that aren’t just Sports and Political Talk.

    And frankly, if someone is just going to put up a computer and walk away for 23 1/2 hours a day, I think there’s no need to renew their license.

    Reply

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