HD Radio development Stasis

I have been working on an HD Radio installation these last few days.  This particular installation was manufactured by Broadcast Electronics.  Some 13 years into the HD Radio development cycle and the implementation still seems like a kluge to me.  To get some idea; to transmit a digital HD Radio with added sub-channels, the following equipment is needed:

  • HD Data importer, off the shelf computer with a sound card and specific software from iBquity.  This is used to import the audio for the HD-2 and HD-3/4 channels.  Runs on Windows (Win 7), Linked to the exporter via IP ethernet
  • HD Radio exporter, another specialized computer with a sound card.  Frames the HD Radio data and adds PID, etc.  Runs on Mandrake Linux, communicates with the exciter via data connection.
  • HD Radio exciter; like other exciters, generates RF and modulates it.
  • HD Radio transmitter; essentially an FM transmitter designed to run as a linear amplifier.

The HD Transmitter part can come in several configurations, including low level combining, high level combining or using a separate antenna for digital and analog signals.

Broadcast Electronics HD Radio transmission system
Broadcast Electronics HD Radio transmission system

None of this is news, of course.  My point is, after ten years, there does not seem to be any further development in HD Radio technology.  In the mean time, competitors are not standing still.  The mobile wireless industry has evolved several times during the same time period; 3G, 4G and LTE have been successfully deployed and widely adopted by mobile phone users.  Truly, mobile data is the real competition to terrestrial broadcasting.

The HD Radio transmission process is an overly complicated patchwork of hardware and software.  The importer in particular seems substandard.  It’s function is to run a bunch of small programs, each doing some small part of the importing process.  The web-admin used Internet Explorer, who uses Internet Explorer anymore?

Since the HD Radio inception, little or no further development seems to have taken place.  There are features, such as album art, program data, traffic data, etc but the system interface is weak, the hardware clunky, the data paths fragile, the operating system outdated, the typical installation is a compromise between cost and available floor space at the transmitter site.

HD Radio is also expensive to deploy and proprietary.  There is little compelling reason to listen to HD-1 channels because the programming is identical to the main analog channel.  HD-2, 3 and 4 channels seem to be mostly used to generate translator feeds, which again, are available with an analog radio.  This use of HD Radio actually damages uptake because, If all the HD Radio sub channels are available on FM analog frequencies, then why even bother with an HD Radio receiver?

Thus the forces at work in the development of HD Radio seem to have reached equilibrium:

Consumer apathy + expensive deployment = 16% uptake on FM and 6% uptake on AM1

The digital radio roll out has been stuck at those levels for many years.  Unless something changes, FM HD Radio will be limited to translator program origination and distribution.  AM HD Radio will go the way of AM Stereo.

1: FCC data on HD Radio deployment; 1,803 of 10,727 FM stations and 299 of 4,708 AM stations have installed HD Radio as of December 31, 2014.

Brother, can you spare a theorem?

A theorem is not, indeed, a fact.  It is rather, an idea which is deduced and supported by other proven facts.  Thus, a theorem is generally believed a truth.  It should be of interest to the “All Digital” AM (AKA Medium Wave) proponents that noise on the digital channel will reduce data throughput as a function of channel bandwidth and Signal to Noise Ratio.  This is known as the Shannon-Hartley theorem:

 C =  B \log_2 \left( 1+\frac{S}{N} \right)

C is the channel capacity in bits per second;
B is the bandwidth of the channel in hertz (passband bandwidth in case of a modulated signal);
S is the average received signal power over the bandwidth (in case of a modulated signal, often denoted C, i.e. modulated carrier), measured in watts (or volts squared);
N is the average noise or interference power over the bandwidth, measured in watts (or volts squared); and
S/N is the signal-to-noise ratio (SNR) or the carrier-to-noise ratio (CNR) of the communication signal to the Gaussian noise interference expressed as a linear power ratio (not as logarithmic decibels).

With this equation, one can discern a fundamental flaw in the all digital logic.  One of the main issues with AM Medium Wave broadcasting is the ever increasing noise floor.  Our society has changed drastically in the last one hundred years or so since AM was invented.  Electrical noise generators; computers, plasma screen monitors, mobile phones, appliances, energy efficient lighting, data over power line, street lights, poor utility line maintenance, even electric cars, it seems, generate a cacophony of noise in the Medium Wave frequency band. A digital modulation scheme, be it HD Radio or DRM, will mask the noise to a certain extent, that is true.  However, once the SNR exceeds the ability of the receiver to decode the necessary bits, the receiver will mute.  While it is true, the listener will not hear noise, they may not hear anything at all.

I will also note; none of the current “AM improvement” schemes under consideration by the FCC addresses the noise issue on the AM band.  Without addressing the noise issue, any digital modulation scheme will be a temporary fix at the very best.  The noise floor will continue to rise and after it gets high enough, the all digital modulation will simply not work.

It will be interesting to see the data from the all digital HD Radio testing that is being done in various locations.  That is, if the NAB, et al. does not decide to treat that data like some kind of state secret; they have become reticent of late.  When somebody acts like they have something to hide, it makes me think they have something to hide…

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

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.