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AM Stereo Renaissance?

At least in some quarters, there appears to be interest in reviving AM Stereo.  Perhaps as an unintended consequence of AM HD Radio, it seems.  Some people have discovered, quite accidentally, that some AM HD Radios will detect the presence of AM stereo pilot and open up with IF bandwidth automatically, making the analog signal sound much better. AM Stereo being received on an AM HD Radio receiver:

That particular brand of AM HD Receiver only allows 5 KHz audio, which still sounds much better than the typical 2.5 to 3 KHz.

A short video comparing AM HD Radio and AM C-QUAM:

As IBOC and C-QUAM are incompatible, it is an either/or situation.  Being that C-QUAM is open source and many new solid state transmitters come with AM stereo cards installed, the financial leap from AM mono to AM stereo is not nearly as steep as it would be to install AM HD Radio.  The other nifty thing;  C-QUAM is it is completely backwards compatible with existing AM mono receivers, the all digital version of IBOC is not.

It bears repeating; AM is not inherently inferior to FM sound.  Wide band AM can sound really, really good.   Something that we seemed to have forgotten over the years of listening to crappy receivers.  This has caught the attention of Tom King, owner of Kintronics, who penned the following letter to the FCC and all AM broadcasters:

Subject: Meeting with FCC Commissioner Ajit Pai and Mr. Peter Doyle,
Chief of the Audio Division of the FCC Media Bureau
at the offices of the FCC in Washington, DC on Tuesday, September 23, 2014.

To All AM Broadcasters in the USA:

Kintronic Labs is concerned about the declining position of the AM radio service in the United States, which we reflected in our Reply Comments to the FCC NPRM Docket No. 13-249 on the subject of “AM Revitalization,” issued on October 31, 2013. In the interest of preserving this great national resource for local public media, we have scheduled a meeting with FCC Commissioner Ajit Pai and Audio Media Chief, Mr. Peter Doyle, to address what we believe are the critical steps toward putting AM radio on a more competitive basis with FM as follows:

(1) FCC enforcement of regulations relative to the power distribution industry and the consumer electronics industry that are not currently being enforced, resulting in a constantly worsening electromagnetic environment for AM radio service.

(2) The need for parity between AM and FM receivers through the establishment of minimum technical standards for AM receivers that would become effective as soon as January 2016. We plan to demonstrate a comparison of full-bandwidth C-QuAM AM stereo reception with a local FM station and with a typical AM receiver in a popular consumer multi-band receiver. The effects of adjusting the AM bandwidth from 2.5 to 10 kHz in 2.5-kHz steps will also be demonstrated.

(3) The need for FCC authorization of AM synchronous boosters. Unlike FM translators, such on-channel boosters would serve to increase the AM stations’ audiences while concurrently maintaining the future viability of the band. The related technique of wide-area AM synchronization for coverage improvement will also be addressed.

Referring to Step #2, it is absolutely essential that very close to full parity be established for new AM radio receivers versus their FM radio counterparts. This includes all key AM receiver performance attributes, including:

Low internal noise floor, well below the average AM-band atmospheric noise level. This includes all internal synthesizer and DSP circuitry within the receiver (and in the immediate environment for integrated automotive applications).
High overall RF sensitivity, selectivity, and dynamic range, to provide adequate amplification of weak signals, even in the presence of significant adjacent- and/or alternate-channel signals, especially in strong-signal environments. This would incorporate typical advanced, multi-stage AGC action, with appropriate interaction between the RF and IF AGC control mechanisms to maximize overall receiver dynamic range, including adaptive front-end attenuation for signal-overload protection in very strong-signal areas. Useful typical specs include: sensitivity – 1 mV for 10-dB SNR; selectivity (adjacent-channel) – 25-50 dB (adaptive).
Highly effective noise (EMI) rejection, including staged RF and IF noise blanking, accompanied by appropriate audio blanking and/or expansion when required. Such features were developed and included in Motorola chip sets in the 1990’s in the AMAX program, and are easily integrated into modern, high-density AM/FM receiver chips.
Full 10-kHz audio bandwidth capability with low detector distortion. This would obviously incorporate dynamic, signal-controlled bandwidth control (including AMAX-style adaptive 10-kHz notch filtering) as dictated by noise and adjacent-channel interference.
Stereo capability. If the receiver has FM stereo capability, it must have corresponding C-QuAM decoding for AM.

Without fulfillment of the first three requirements (this also includes the associated AM antennas both for vehicles and for home use), basic AM reception will suffer significantly compared with FM. Without the last two, the output sound quality cannot be closely competitive with FM (i.e., 10-kHz full bandwidth on AM versus 15-kHz nominal for FM).

We therefore petition the FCC to mandate the following minimum allowable performance specifications for all AM receivers that will be manufactured and installed in new automobiles as of January 1, 2016:

Audio Bandwidth: 10 kHz typical, adaptive, with a minimum nominal bandwidth of 7.5 kHz
Signal-to-Noise Ratio: minimum 55 dB, preferably 60 dB
Sensitivity: -120 dBm for a signal-to-noise ratio (SNR) of 10 dB
Selectivity: 25-50 dB (adaptive filtering, using co-, adjacent-, and alternate-channel detection)
Dynamic Range: 100 dB
Noise Figure: 1 – 3 dB
Image Rejection: -50 dB
Intermod: IP2 , IP3 intercepts +10 to +40 dBm
IF: low with image-rejecting down-conversion, or double-conversion
Stereo Separation: minimum 25 dB

Respectfully Submitted,
Tom F. King
President

All of those technical specifications are doable with modifications to the current receiver chipset.  Currently there are very few if any AM Stereo receivers being manufactured.  One might ask, how can a typical AM mono receiver be modified to receive AM Stereo.  A great question.  For a small sum, an outboard circuit board can be purchased and installed in a typical AM mono receiver.  For most non-car radios, this modification would be fairly easy.  Car radios, on the other hand, will be very difficult to modify since most new radios will be bricked if tampered with (thanks a lot, crackhead radio thieves of New York).

And for those interested, there are also lists of radio stations broadcasting in AM stereo:

According to the Wikipedia source, there are 90 some odd station using C-QUAM AM stereo.  Using iBquity math, that is nearly the same number as are broadcasting AM HD Radio.

If you are an AM station owner, you can start by transmitting good programming.

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10 comments to AM Stereo Renaissance?

  • I remember back in the 1980’s when I engineered WMMM-AM in Westport we were running the Kahn ISB AM Stereo system. I personally think it had a edge over Motorola’s C-QUAM. I remember listening to a competing station at night and hearing the platform motion which would make the listening experience quite annoying if not downright nauseating.

    I have one of the Accurain / Radio Shack radios which decodes C-QUAM AM Stereo quite well. I haven’t had the opportunity to try it with the DaySequerra M2 mod monitor I have in the studio. Among the radios in the collection are several AM Stereo models including the Sony SRF-A100 table portable, SRF-A1 and SRF-42 Walkmans, CFS-6000 boombox and the XR-A33 car radio.

    The only thing about the higher quality AM Stereo radio manufactured during AM Stereo’s popularity was they went out of production prior to the NRSC-1 mask mandate. By this time AM Stereo was already beginning to lose traction due to the lack of FCC issuing a standard transmission method.

    I personally think that terminating the use of IBOC on AM and going back to AM Stereo might be a start to reviving interest in the AM band, in addition to combating the growing environmental noise. Of course, quality programming that serves the local community might serve as a reason for people to tune in.

  • KPL

    “Some people have discovered, quite accidentally, that some AM HD Radios will detect the presence of AM stereo pilot and open up with IF bandwidth automatically, making the analog signal sound much better”

    The IF bandwidth should be opened up automatically to the full bandwidth of a non-HD AM broadcast regardless of mono or stereo, if reception conditions are good enough.

    The above reported trait of these receivers could lead to AM stations transmitting a stereo pilot with audio that continues to be mono, which surely is undesirable? A stereo pilot should only be transmitted if there is actual stereo sound on the station, it shouldn’t be necessary to transmit a stereo pilot to optimise the audio fidelity on a station with mono audio.
    What receivers behave as above and is it possible for the user to manually select AM bandwidth themselves?

  • http://www.radioworld.com/TabId/64/Default.aspx?ArticleId=272609

    Two stations in Seattle will apparently be testing all-digital AM this weekend; analog listeners will hear silence…

  • Tom Reitzel

    Indeed, good programming is a great start. Although I was vaguely aware of AM stereo back in the 1980s, I was too engrossed in newly networked microcomputers via CompuServe during that period to pay much attention to AM stereo. I and many others had left broadcasting behind by the middle of the 1980s. AM stereo never had the chance that it really deserved. Frankly, the FCC’s mandatory standard of C-QuAM hasn’t helped much to increase the appeal of MW to the masses. Today, FCC’s 1993 mandate of C-QuAM has now become just one more factor which is limiting innovation on the MW band. Without a mandatory standard, we might have a digital format combining ISB AM stereo and VOA’s radiogram.

  • Nicholas M

    I can attest to the “open source” nature of the Motorola AM stereo system as I have a part 15 legal 100 mW transmitter running it which was built from a kit! The transmitter is being driven with a computer running broadcast quality audio processing with the proper NRSC bandwidth limiting, asymmetrical peak limiting as per FCC specs, and the audio is processed as L+R and L-R rather than discrete left and right as FM is. I personally have several wideband AM tuners and that includes a few AM stereo tuners such as the first portable sold to the public starting in 1983, the Sony SRF-A100 which despite being 30 plus years old works as it did back then.

  • Neil

    AM stereo is better than AM mono, but I cannot think that music on AM will ever be what it was in the 60’s. We should adopt the simplest AM stereo system possible. C-QUAM receivers are more of the issue than the transmission format. I have a Sony SRF receiver that has receives C-QUAM but does not require a pilot tone, which is low frequency.

  • Neil

    If more radios had that, it would be a more useable format. But often there is no way to bypass the blend or mute circuit when the station has fading. There are also digital ways to improve phase shift issues post decode of a c-quam stereo signal. I like AM stereo, it is just that the implementation of it was not good It needs to be simple enough to incorporate into an FM stereo decoder chip.

    It sounds like a good idea, but I don’t like this whole synchronized to GPS concept, for the simple reason that GPS satellites will eventually fall out of orbit. This creates a dependency of operation on another source. High frequency tones can be filtered out by adding user adjustable filters to receivers.

    The biggest problem is that AM radio receivers are still living in the 50’s as far as design. Most of them have poor antenna tuning and directional antennas. One of my ideas is to develop an AM receiver system that has multiple directional antennas that will allow the radio to track the signal and automatically locate the best angle. Also, a vertical / horizontal directional antenna system could be used to phase out or minimize skywave interference. I have tested this using two matched receivers and coaxial loops, where one loop was used for ground wave and the other loop was used for skywave, but canceled out the groundwave. Thus, I could easily separate groundwave from skywave and develop a system to automatically use the best signal….in the future I would like to find some way to do phase cancelation.

  • Neil

    The FCC also needs to help AM broadcasters cooperate in handling sun down interference. Day / Night pattern is not a perfect science. In Central Wisconsin, we have 3 stations at one time on AM 1130. As the sun goes down, Detroit and Minnesota interfere with Milwaukee. The logic would be to have detroit and minneapolis drop their power earlier. This should not affect their normal listening area because their signal is carrying much farther for the moment. It is more that 3 interfere at one time. At times of the year, HD radio causes more static and noise, but is not able to be heard anyway.

    Blame analog AM for noise and interference – because digital is the cause.

  • Neil

    The need for FCC authorization of AM synchronous boosters. No, this can’t work.

    I say, absolutely not. I am already concerned that we have synchronous boosters that are pirated broadcasts on AM, using a phase locked loop method to locally cut over an AM station and insert its own broadcast and political agenda. AM radio should always be single source. Otherwise we could have media chaos and manipulation similar to fascism.

    “The need for FCC authorization of AM synchronous boosters. Unlike FM translators, such on-channel boosters would serve to increase the AM stations’ audiences while concurrently maintaining the future viability of the band. The related technique of wide-area AM synchronization for coverage improvement will also be addressed.”

    The concern I have is, first, there are physics issues with this, and second, national security. We need long range AM radio so that the public can verify news and information. Next thing that will happen will be that we will have media companies sending different advertising to different markets on the same frequency. This would be great, but would render the media useless. Throw a pirate in there or two. I heard that on WTMJ…..which WTMJ? One license per station please. What purpose would there be for an AM booster?

    This was tried on FM on different frequencies in Canada in the 90’s, where one company broadcast the same music on many stations, but inserted local advertising. That company is not in business anymore!

  • Christopher Boone

    KLLS joined the Cquam family at 12:01am 6/26/16 playing Classic Top40. Motorola 1300 exciter into a Gates DAX3.

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