Looks like the AM HD Radio™ juggernaut continues… To sink under its own technical faults that is. According to the list the number of AM stations running IBOC in the US is now down to 233 stations from a high water mark of 290 or so. That represents a total of just 4.8% (233 IBOC/4782 Total stations) of all US AM radio stations. On a related note, Bob Savage of WYSL 1040, Rochester, NY has a good idea:
I’ve always said – if you want to see surprising new life in the AM band, s**t-can the stupid irrelevant NRSC pre-emphasis filter and allow stations to run to 15 kHz during daylight hours and 10 kHz nighttime. Mandate C-QUAM in all receiver and receiver devices.
It will sound better than HD, be more robust, and cause far fewer problems. Plus it wouldn’t obsolete a single radio out there, while making a whole bunch of them sound a whole bunch better.
It is so simple in concept, so easy to implement, with almost no expense to AM stations. Again, Mr. Savage:
Most software-based processors have com ports which can be addressed by a remote control system like Sine Systems, so when the power gets reduced at evening pattern change, the bandpass can be changed at the same time…..vice-versa at sunup. No biggie.
For older setups a simple outboard relay and rolloff network could accomplish the same thing. It’s a little more complex but again, not a big deal.
Wow. Facepalm.
Wish somebody had thought of that a few years ago, it might have saved several million dollars and we’d have a different AM band today.
There are a few shoehorned AM stations around here that might be adversely affected by 15 KHz daytime bandwidth, but those are few and far between. By and large, most stations are spaced correctly where this could really work and work well. It certainly would not generate the chaos that AM HD Radio™ has.
The standard FM channel in the United States, as defined by the FCC is 200 KHz (See CFR 47 73.201). The occupied bandwidth of an FM IBOC signal, as created by Ibiquity, Inc., is 400 KHz. See the below picture:
HD radio trace on FSH3 Spectrum Analyzer
A picture is worth a thousand words. Engineering types will understand this without explanation. For non-engineering types, here are your thousand words (or so):
On the left-hand side of the screen is the signal strength scale. Each vertical division is 10 dB. This is not absolute signal strength, it is referenced to -20 dBm. However, it gives a good relative signal strength for both the analog carrier and the IBOC carriers. The analog carrier is centered on the screen, it slopes upward like a steep mountain, peaking at -50 dBm relative. The IBOC carriers are on either side of the analog carrier, they are flat, approximately 75 KHz wide, and peak approximately 20 dBm below the analog carrier (-20 dBc). For some reason, likely the bandwidth and/or impedance match between the antenna, high-level combiner and the two transmitters, the left IBOC carrier is actually peaking around -14 dBc.
The span, as noted on the bottom right-hand side of the screen is 500 kHz. Each horizontal division is 50 KHz. The entire span of the measurable signal is eight horizontal divisions, thus 400 KHz.
As noted above, the allocated channel bandwidth is 200 KHz, thus this station is exceeding it’s allocated bandwidth by 100%. This is allowed under CFR 73.404, which is titled “Interim hybrid IBOC DAB operation.”
IBOC proponents will make the argument that FM radios work on something called “The capture effect,” which is to say that if two signals are on or close to the same frequency, only the stronger signal will be demodulated. Thus, the IBOC carriers have no effect on the adjacent channels that they are interfering with so long as the adjacent signal is stronger than the IBOC carrier. The argument is further carried forward by assuming that with a station’s protected contour (60 dBu in most cases), the IBOC carrier will never exceed that analog carrier.
That is not necessarily true, especially in areas where terrain (and buildings, underpasses, unintentional directionality in transmitting antenna, etc) can attenuate signals close in causing the IBOC signal to become equal to or stronger than the adjacent analog signal. This effect causes picket fencing. Lower powered FM stations; class A, LPFM, etc, are especially vulnerable to this effect.
Further, even in areas where the analog carrier is stronger than the IBOC carrier, the noise floor has been moved from -100 dBm or so to -70 dBm, which is a 1,000 times greater. To assume that raising the noise floor by 1,000 times will have no effect is, as they used to say in the Navy, making an ASS out of U and ME. Mostly you, in this case. This affects the receiver by making it less sensitive, it will also add noise to the demodulated signal as the elevated noise floor will show up as background hiss. Even further still, higher IBOC carrier levels, as authorized by the FCC in January of 2010 can interfere with the station’s own analog carrier.
According to both Ibiquity and the FCC, which stated in the Notice of Proposed Rulemaking, the reason for interim IBOC operations are:
iBiquity’s IBOC DAB technology provides for enhanced sound fidelity, improved reception, and new data services. IBOC is a method of transmitting near-CD quality audio signals to radio receivers along with new data services such as station, song and artist identification, stock and news information, as well as local traffic and weather bulletins. This technology allows broadcasters to use their current radio spectrum to transmit AM and FM analog signals simultaneously with new higher quality digital signals. These digital signals eliminate the static, hiss, pops, and fades associated with the current analog radio system. IBOC was designed to bring the benefits of digital audio broadcasting to analog radio while preventing interference to the host analog station and stations on the same channel and adjacent channels. IBOC technology makes use of the existing AM and FM bands (In-Band) by adding digital carriers to a radio station‘s analog signal, allowing broadcasters to transmit digitally on their existing channel assignments (On-Channel) iBiquity IBOC technology will also allow for radios to be ”backward and forward” compatible, allowing them to receive traditional analog broadcasts from stations that have yet to convert and digital broadcasts from stations that have converted. Current analog radios will continue to receive the analog portions of the broadcast.
Few if any of those goals have been met. As far as the forward/backward compatible thing, it just isn’t so unless a person actually owns an HD Radio. As noted in previous posts, few consumers have seen fit to purchase an HD Radio, nor have car manufacturers taken to installing them en mass in new cars, so there is no forward compatibility. Instead, we have FM radio stations interfere with each other and themselves in an attempt to “modernize” the audio broadcasting business. This is a bigger problem for small, community radio stations that can neither afford to install the expensive, proprietary HD Radio system nor broadcast quality receivable signals with an adjacent HD Radio signal raising the noise floor by 1,000 times or more.
I can think of no other greater threat to free over-the-air broadcasting than HD Radio and the degradation of AM and FM services that come with it. The consumer has shown that they don’t care. If given the choice between free over-the-air broadcasting that has mediocre programming and is full of interference, and some type of paid internet streaming service that sounds reasonable with good programming, they’ll go for the latter.
In short, some cobbed-together digital modulation scheme is the last thing that radio needs right now.
I have received an e-mail from occasional reader John, who comments that many of the Windy City AMs have turned their buzz saws off. I note today, that the same can be said for many of the NYC AMs. WABC has had its IBOC turned off for quite some time. The latest to turn off is WNYC on 820 KHz. Several people have noted the loss of noise on their signal this morning.
According to Ibiquity’s own website, only six AM stations in the NYC market are currently using IBOC.
What does this mean?
Could it be that management is finally realizing that the cure is worse than the disease? The disease is alleged poor audio quality, and the cure is IBOC itself.
I found this picture of Bob Struble’s vacation last summer:
HD radio flagship
To the uninitiated, this might seem quite alarming; boat sinking, rigging all ahoo, this poor guy waiting for rescue or certain death. But to understand what is going on here, you have to see the whole picture. Things are not what they seem, in fact, it’s designed that way:
The rest of the story
All this time, I have been lamenting the technical flaws IBOC, when really; its supposed to do that. Holy cow! All these years of wondering, “What the fuck are they thinking?” and decrying HD Radio, especially AM HD radio. Boy am I embarrassed. Makes me want to do this:
Baghdad Bob Bob Struble latest quote, brought to bold typed prominence on the pages of Radio World magazine: “Consumers now expect to see album covers when they listen to music.” I think he means album art, but anyway.
You mean to tell me HD radio is failing because of lacking album art! Of all the Bob Struble quotes, to prominently feature this one in their article makes me think 1) the editors at Radio World have a sense of humor, or 2) they have a sense or irony, or both.
So anyway, there you have it: Album Art. The rest of the so-called technical flaws are “design features” that will enhance HD radio in the long run. They’ve got us right were they want us.
