HD radio – Page 5 – Engineering Radio

The AM HD all digital test, Part I

After reading this article in Radio World it seems the all-digital AM testing completed last December was “nearly flawless.” This comes as no surprise considering that WBCN is owned by CBS, also an iBiquity investor. Could there really be another result? I think not. But let us examine the technical aspects of the WBCN test itself.

WBCN is on 1,660 KHz in the expanded part of the AM band. According to the FCC database, it transmits from a single 90.7 degree tower. As such, the tower is likely either broad-banded already or easily modified to be. Also according to the FCC database, there are eight other stations licensed to 1,660 KHz, all of which transmit with a power of 1 KW at night. This eliminates much of the interference issues found on the rest of the AM band. It can be further noted, the problem with electrical noise is most prevalent below 1,000 KHz. There is little wonder in the nearly flawless results.

From a technical standpoint, this is about as favorable a testing configuration as can be conceived for AM IBOC. If AM HD radio did not work under these test conditions, then it would never work at all. The actual data from the tests has yet to see the light of day and it may never be released. This is likely due to the same reason the NAB will not release its technical improvement study on AM; we simply won’t understand it.

Near the end of the article, someone (it is not exactly clear who) asks the NAB, “Why the opacity?” For which the answer given is “to get stuff done.” There is a fair bit of hubris in that statement. Is the NAB now the technology decider for the rest of us? I think not. Shutting out everyone but a very select few rightly causes suspicion, something that the Radio World article acknowledges.

Accurate, real-world testing involves more than using one technically favorable test subject. In fact, the tests should be run in the most technically challenged environment to present meaningful data points in real-world conditions. Stations like a six-tower directional on 580 KHz, a 190-degree tower with a folded unipole on 810 KHz, or pretty much any class C AM station at night time. These types of tests will represent at least a few of the existing antenna systems and stations. Will that happen? It depends on whether the FCC will hold somebody’s feet to the fire and demand meaningful testing.

Much ink has already been spilled by various trade publications debating the future of AM broadcasting. Most take the position that there are several technical issues that make AM broadcasting problematic if not downright untenable. There are indeed some technical issues with AM when compared with FM or IP-based audio distribution. There are also several ways that AM broadcasting is superior to both FM and IP-based audio distribution. The truth is that AM broadcasting’s issues are complex and involve technical, regulatory, and operational considerations.

These can be broken down as follows:

AM is prone to electrical noise interference
AM is prone to co-channel and adjacent channel interference
AM has inferior bandwidth and thus the audio quality
AM has poor signal quality
AM has a low or no market share

All of these problems conspire to make AM broadcasting unprofitable, or so the narrative goes. Does all-digital AM HD radio really solve any of these problems? From the WBCN test alone, the results are inconclusive.

Transmitting a signal in digital format does not make it immune to noise or interference. It simply masks the interference until the noise floor becomes too high causing excessive bit errors, at which time the receiver mutes. Thus, with AM HD radio in a noisy environment, the listener will not hear static, that much is true, they may not hear anything at all. Is this all-or-nothing reception an improvement?

AM broadcasting audio bandwidth problems are mostly self-inflicted. AM stations created loudness wars in the 60s and 70s, causing splatter and adjacent channel interference on older, cheap diode detector-type receivers. Receiver manufacturers responded by limiting IF bandwidths to 3-4 KHz, slightly better than telephone quality. The industry came up with the NRSC-1 standard which limited AM bandwidth to 10 KHz or less. For a long while, AM radio receivers remained very poor. This appears to be changing with newer receivers that are both more selective and more sensitive. My Toyota has a Pioneer radio which has good bandwidth on AM. Is it as good as FM? No, but it is certainly listenable, especially if no other station is playing that style of music.

That brings me to programming, which is the real crux of the issue. Continued in part II.

Brazil: The place where they test tech before it is implemented

After extensive testing of Both HD Radio and DRM, the Secretary of the Ministry of Communications Electronic Communications, Genildo Lins, said the tests of the two technologies have had poor results, especially high-power FM . The testing demonstrated the digital signal coverage is approximately 70% of the current analog signal. “The future of radio is digital, but that future is not yet. We are unable to make a decision on these results.” A polite way of saying “This is not the digital radio we were hoping for.”

These are just a few brief excerpts of the FM HD Radio test reports from Sao Paulo. The method of testing:

The transmission system was located in the center of the city of São Paulo. The signal HD Radio digital broadcast was extended hybrid mode combined with the analog signal in the air, with separation of 163.8 kHz from the carrier’s analog FM signal and the carriers of HD Radio digital signal in sub-upper and lower sidebands. The power used in transmitter for the analog signal was 27 kW, and for the digital signal of 1 kW. Attaching the FM and HD Radio systems in their respective transmission antennas, the power Isotropic Effectively Irradiated (EIRP) of the analog signal was 112.3 kW and the digital signal of 1.12 kW. Thus, the protection ratio (EIRP power ratio between the analog and digital signals) was 20 dB (sic). During the measurement campaign, two commercial FM receivers were used analysis of analog reception, both to verify their potential impacts on receiving due the introduction of the digital signal, as to assist in verifying the coverage area of the signal analog.

The results of this testing:

Checking the results on each route, the route R1 radial (southeast direction), the stretch P1 to P2, that extends to 10.88 km (7.3 miles) of distance from the transmitter, the audio decoding was 71.6% of the digital audio frames received, and in the remaining sections of the route were little digital coverage.

In radial route R2 (southwest direction) was decoding of digital audio throughout the stretch to P1 P2, which extends up to 10.7 km (6.6 miles) of distance from the transmitter. In the following passage (P2 P3), the first blend was 17 km (10.5 miles) from the station. Following the passage P3 to P4, 26.4 to 44.9 km (27.9 miles), there was only 21.8% decoding of digital audio frames received within that stretch. In the last section (P4 to P5), from 44.9 km, there was almost no coverage digital.

In R4 route (northwest), there was decoding of digital audio throughout the stretch P1 to P2, extending up to 11.8 km (7.3 miles) of distance from the transmitter. In the following passage (P2 P3), from 11.8 to 24.9 km, was 62.5% of decoding digital audio frames received within that stretch. Following the stretch from 24.9 to 47.5 km (29.5 miles), (P3 to P4) the percentage was 24.3%. In the last stretch, from 47.5 to 61.7 km (P4 to P5), no digital coverage.

In route R6 (northeast direction), the stretch up to 9.8 km (6 miles), (P1 to P2) was 74.7% decoding of audio frames. In the passage P2 to P3 from 9.8 km to 29.8 km (18 miles) of the station, there was audio decoding 100% of the received frames. Following the stretch from 29.8 to 45.3 km (28.1 miles) (P3 to P4), the percentage was 87.2%, and in the last stretch, from 45.3 to 60.9 km (P4 to P5), the percentage was 47.9%.

Routes are shown on a map:

Using unbiased real-world testing, HD Radio does not look so hot. One caveat; the digital carrier level is -20dBc. That being duly noted, results show a 112 KW EIRP analog station with a 1.12 KW digital carrier that is unusable 6 miles from the transmitter site in some areas. It is almost hard to believe. Original documents can be found on the Government of Brazil Ministry of Communications website (in Portuguese). They are interesting reading, although you may need to parse them through Google translator.

AM HD Radio (no surprise) and DRM have similar or worse results.

Thus the myth “Digital is better,” is called to question. I am not opposed to new technology, provided it works better than the technology it is replacing.

The NAB’s AM study

As has been widely reported in other places, the NAB (National Association of Broadcasters) has completed its study of AM Radio and recommendations to improve the service. The NAB has taken a cautious, if the not somewhat paternalistic approach of holding the report while they review their options. It seems that the technical nature of such a document would not be understood by us mere mortals.

Some of the AM improvement options that have been bantered about in the past include:

Moving AM stations to the vacant frequencies of TV Channels 5 and 6, see this.
Reducing the number of AM stations on the band, see this.
Increasing transmission power of AM stations, see this.
Converting AM stations to all digital modulation, see this.

There may be a few other options considered also.

It does not take too much analytical prowess to deduce where the NAB’s proposal is going. My prediction is that they will be promoting an all-digital “solution” to the AM broadcasting issue using iBquity’s HD Radio product. I base this prediction on the fact that all of the major radio members of the NAB (Clear Channel, Cumulus, CBS, et al) are heavily invested in the iBquity product. For this reason, the NAB will find (or has found) that digital broadcasting in the medium wave band will solve all of the currently perceived problems with AM and everyone should embrace the technology.

A few numbers to note:

iBiquity and the FCC data base reports that there are currently either 270 or 299 AM stations licensed to operate with HD Radio. Other sources note that several of these stations have been turned off and the actual number using HD Radio is 215.
There are 4754 AM stations licensed by the FCC.
Currently, HD Radio is transmitted 4-6% of the AM stations in the country.
It costs $25,000 US to license a single HD Radio station through iBiquity. They are, however, discounting that to between $11,500 and 13,500 and have a convenient payment plan (limited time offer, expires December 31, 2012, FCC license fees are extra).
It costs between $75,000 and $150,000 to equip and or modify a single AM station with HD Radio gear.

Unless iBiquity drops all patent claims and licensing fees to use its product, an FCC mandate for AM stations to install HD Radio would be skating dangerously close to corporate fascism (AKA Mussolini Fascism or Corporatism) as one corporate entity would then control broadcast radio by licensing its modulation scheme. And no, the patent is not going to expire.

Digital modulation schemes used in the medium wave band have their own set of technical issues. HD Radio is not the panacea for AM broadcasting’s self inflicted woes.

AM Radio Improvement Plan

There has been lots of hand wringing and ink spilled regarding the sorry state of affairs in the senior service. AM is plagued with problems; interference, poor bandwidth, etc. To that end, the NAB has launched studies and initiatives and hired all sorts of pricey consultants to consult with. Here is my own AM improvement plan and it is rather simple:

Clean up the transmitter site.
Get rid of AM HD radio.
Variable IF bandwidth receivers.
Improve Programming.

How many of us have seen AM transmitter site dumps? Deferred maintenance, malfunctioning directional arrays, trees growing up on the ground system, flooded buildings and ATU’s, rusty towers, transmitters not a full power, ground system deteriorated or missing all together, just to list a few problems. Many AM transmitter sites are technical disasters. Think that these things have no bearing on the AM station’s signal? Think again.

differed maintenance, AM transmitter site — Differed maintenance, AM transmitter site (there is a tower in there somewhere)

Trees growing around the tower base can attenuate the signal by 30%. A comment from a well known engineering firm:

…Recently XXX field engineers had occasion to measure an AM station at XXXX kHz before and after removing vegetation in the vicinity. The station had a quarter-wave tower. The base area had grown up in brush and hardwood trees to a height of perhaps 30 feet (9m) and this extended from near the base across the entire ground system. After clearing (cutting, no ground system disturbance), the signal measured at some 16 locations on four radials went up a uniform amount of about 15% or 1.2 DB. That’s about a 30% increase in radiated power…

That is an inexpensive power boost and they didn’t even have to file with the FCC! A 1 – 2 dB power gain is pretty nice and can mean the difference between a listenable signal and static. How many times have I heard the lament that AM band is full of noise and not listenable. Certainly, there are major challenges in the urban listening environment. Putting forth a better signal will overcome some of this electrical noise.

There is a reason why engineering standards were developed for the physical plant; they work.

There is no cure for the noise that AM HD Radio puts out into the adjacent channels. This self interference benefits none, not even the station transmitting AM HD Radio. This dubious technology has proved itself a non-starter and should be discontinued. For smaller station owners, the cost of implementing AM HD Radio is prohibitive. Licensing of a proprietary modulation scheme, new transmitting equipment, specialized exciters plus any needed bandwidth improvements to AM antenna arrays can easily exceed $100,000.00. Unfortunately, it is often the small AM radio operators that are making a good showing, and serving their community of license and making money. These are the very stations that are hurt the most by adjacent channel AM HD Radio interference.

Receiver design over the last twenty to thirty years has been the greater issue with perceived low AM broadcast quality. AM receivers have an average bandwidth of just 3-4 KHz, which is slightly better than telephone quality. AM broadcasting has gotten a bad wrap because of this and there are many comments about how AM is “inferior quality” to FM. With a quality older receiver, AM can sound very good. Of course, the receiver manufactures all point adjacent channel interference as their rational for reducing IF bandwidth. Why not leave it in the hands of the user? The GE Superradio had this feature with a “wide” and “narrow” setting for AM reception. They worked remarkably well. A receiver could also be designed to automatically increase IF bandwidth at higher received signal strengths.

Finally, as the saying goes; Garbage in, Garbage out (GIGO). This holds true for many things including radio programming. Expecting that mediocre satellite syndicated news talk will garner great ratings and huge revenues is silly. For years and years, station owners have put minimal effort into AM radio and expected big returns. It is not working. AM stations that go against that trend; those with unique formats (Gasp! Music, on AM?), local content, and community oriented programming can and do succeed. They are fighting an up hill battle in both directions. With all of the business pressures from larger broadcast groups, interference issues and negative viewpoint on the viability of the AM band, one wonders how long they can last.