HD radio – Page 3 – Engineering Radio

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:

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

Where:
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
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.

CES 2014 and the Digital Radio question

I have been busy of late, however, still keeping abreast of the news of the day. Along with that, CES 2014 wrapped up recently. No huge developments, especially when it comes to Broadcasting. However, there was one item of interest; the updated technical specifications of IEEE 802.11ac.

It is of interest here because of the implications of the mobile/portable data developments and their impact on traditional AM and FM broadcasting. The new specification calls for 1.2 Gbp/s per device in the initial release, increasing that throughput to 6 Gbp/s in later releases. These data rates are for overall transmission, including the WiFi overhead. Actual usable application data (layer 5-7) would be about 20 to 30 percent less. Even so, 900 Mbp/s is a phenomenal data rate. Truely I say to you; this is the future of digital broadcasting. HD Radio™; it may well prove that the “HD” stood for “Huge Distraction.”

The new 802.11ac specification uses MU-MIMO, high density modulation, larger channel bandwidths, and beamforming technology in the 5 GHz WiFi spectrum. Of course, the question is, at what distances will this system work? If it is like conventional WiFi, then 100-200 feet is about all that can be expected. However, there are also many people interested in wireless broadband (WiMAX) service as an alternative to traditional wired ISPs. For that application, having many outdoor 802.11ac nodes connected by a backbone could potentially blanket a city or campus with free high speed wireless data.

Along the same lines, there are many people involved in creating mesh networks of various types; be they ad-hoc mobile networks, darknets, bitclouds, etc. Mesh networking is a very interesting topic, for me at least. The network protocols are getting better and more secure. WiFi hardware is becoming less expensive and more reliable. As more and more people put effort into developing protocols like cjdns, local mesh networks will become wide spread, unless they are outlawed. You know; because of teh terrorism!!1!!

As it stands today, I can drive for two hours in mostly rural upstate NY and CT streaming my favorite radio programs and have nearly seamless hand offs and very few dropouts. This is on my three year old, beat up 3G HTC android phone sitting in the passenger seat of my car.

Digital Radio is here, it is simply not the In Band On Channel system that legacy broadcaster’s have chosen.

Happy New Year

I wish everyone a Happy New Year and hopefully, a prosperous 2014.

Another year has gone by, and there were few things remarkable about it. Among those are:

From the digital radio front; HD Radio continues to be a non-factor in the bigger broadcasting picture. FM HD Radio continues to make very small inroads, especially with public radio groups who’s HD Radio expenditures are mostly tax payer subsidized. AM HD Radio continues to backslide slowly from it’s high water mark of 310 stations in 2007. It is difficult to nail down the exact numbers of AM HD Radio broadcasters, however, Barry McLarnon notes that 177 stations are currently transmitting AM HD Radio. No official numbers are available from either the FCC or iBiquity itself.

The great 2003 translator log jam (Auction 83) was finally fixed so that the FCC could move ahead with the LPFM application window in October. In the end, some 1,240 translators were granted, with more conflicting applications still in the works.

The LPFM filing window opened in October amid the government shutdown. Many groups were predicting 10,000 new applications for 100 watt LPFM licenses. The actual number is closer to 2,800. The final number of Construction Permits issued with likely be somewhat lower as defective and competing applications are dismissed. This number seems low to some LPFM proponents. When I approached a local interest group about launching a low power radio station, I was basically met with indifference. With a very complex set of application guidelines and operating rules, plus very low power levels, it is not surprising at all.

The NAB and the FCC have been working diligently on revitalizing the AM broadcasting band. Results of these efforts are yet undetermined as the proposal works it’s way through the regulatory process. The so called “analog sunset” still lurks in the background somewhere, waiting to be trotted out at the most opportune moment. I remain skeptical of the current proposal.

Cumulus Broadcasting purchases Dial Global and renames it West Wood One. Some people lose their jobs.

Nielson buys Arbitron rating service and renames it Nielson Audio. Some people lose their jobs.

Clear Channel tries to fly under the radar with “staff reductions.” Some people lose their jobs.

Long time online radio forum “Radiodiscussions.com” ceased existence. Starting out as Radio-info.com in the mid 1990’s, radio discussions was largest, longest running radio forum in the country. It held tens of thousands of posts on almost every radio topic under the sun. Unfortunately, it was bought and sold a few times over the last few years and the new owners could not figure out how to monetize it. The end.

Bernie Wise passed away on December 13th. This is truly unfortunate as Bernie was a character perfectly suited to the radio business. He started working for RCA and is responsible for UHF television broadcasting in the US.

On the blog front, we continue to grow in page views and readers. As of this date, Engineering Radio gets approximately 540 page views per day and has 227 RSS subscribers. The split is 60/40 percent domestic/international readers. The top five international traffic sources are; Canada, UK, India, Germany and Brazil.

There are some 634 articles with 2,640 legitimate comments and 429,600 spam comments.

Regarding site outages, there were 343 minutes of server down time. Two DDOS attacks lasting six and three hours respectively and one incident of a corrupted .htaccess file rendered and error 500 message for six hours. Total down time 1,243 minutes or 20:43 hours which gives a 99.87% availability for the website. Not bad, but we can do better as the uptime goal is 99.99%.

On a personal note, my college studies are progressing well. I have three more classes or 10 credit hours left until I am done. My GPA is 3.90 which is not terrible considering I am working full time and going to school almost full time. Truth be told, I cannot wait until it is finished.