Sunday, December 16, 2018

Late 2018 IBOC Report, KNX-1070, KSL-1160

We talked at some length a few years ago about IBOC, or so-called HD radio. At the time, iBiquity Digital Corporation was the sole licensed vendor for the U.S. That has changed.


Old news by now, in October, 2015, Dedicated To Sound, Inc. (a.k.a. DTS) purchased the rights to this HD Radio technology from iBiquity and is now the new sole owner.

DTS announced thusly:

"DTS is excited to announce it has entered into a definitive agreement to acquire iBiquity Digital Corporation, the developer of digital HD Radio technology for AM/FM audio and data broadcasting for approximately $172 million. DTS expects to finance the transaction through a combination of cash on hand and debt."

iBiquity was the exclusive developer and licensor of HD Radio technology, the sole FCC-approved method for upgrading AM/FM broadcasting from analog to digital. iBiquity’s partners included leading automakers, consumer electronics and broadcast equipment manufacturers, radio broadcasters, semiconductor and electronic component manufacturers and retailers.

The market that has shown some success is the automobile HD Radio market. The home market has not. Said DTS, "This transaction extends our strategy of delivering a personalized, immersive and compelling experience across the network-connected entertainment value chain, and complements our existing suite of technology and content delivery solutions while enabling us to strengthen our position in the large automotive OEM market. Consumers have come to expect a higher quality sound experience in their car, and we believe there is a tremendous opportunity for DTS to capitalize on the upgrade to HD Radio technology as cars are increasingly equipped with screens and advanced entertainment systems.”

iBiquity had successfully driven penetration of HD Radio technology in the North American automotive OEM market. HD Radio technology was built into approximately 35% of cars sold in the U.S. in 2014, and DTS expects the majority of North American vehicles to come equipped with HD Radio technology over time.


The IBOC acronym stands for "In Band On Channel". Currently in the U.S., a hybridized version of the digital signal is imposed on the analog signal and the result transmitted. This is supposed to be an interim or transitional method. Stations that are licensed through the FCC for the digital add-on and have entered into contract with iBiquity and now DTS may transmit the hybrid signal. Current FCC records show a total of 237 stations are authorized to transmit IBOC hybridized digital. Many of those who made the initial licensing effort to get a digital signal on the air have terminated transmission due to resultant nighttime skywave interference problems on the broadcast band.

The misnomer here, at least for the hybridized version, is the term "On Channel". The 15 KHz digital sidebands either side of the main carrier bleed fully beyond the adjacent AM channel center and into the adjacent station's far sideband. Let me state this is another way: They have positioned the digital sideband information on the adjacent channel! No filter, on any receiver, regardless of bandwidth, can reject it. However, testing has shown some receiver's passbands are better than others. In order to provide room for these expanded sidebands superimposing digital information on top of analog audio, stations also have had to narrow their audio response to an absolute 5 KHz maximum, further reducing standard analog audio quality. Adherence to strict technical standards is now an absolute imperative, both in the transmitter, modulation technique, and antenna or you have an even worse interference problem. And we all know radio stations often fail in this area of strict adherence. This, currently, is what the FCC calls "Hybrid" digital operation, the precursor to going fully digital at some future date.


On the AM broadcast band, where this will all end up is anybody's guess. Will it ever go entirely digital? I suspect not, at least for the foreseeable future. The number of facilities registered to transmit hybridized IBOC digital has remained fairly stable over the last couple of years. In 2009 as IBOC was ramping up, 289 facilities were registered with the FCC. That number reached 293 a year later in 2010. Since the peaks of the initial few years, however, the overall decline has been sure but steady.

TopazDesigns runs a nice U.S. AM and Canadian AM station search site. Within it is also a page kept current with the latest IBOC stations on the air. Their current count as of this date shows only 117 transmitting, and only 35 at night. As is evident, interest has waned for digital on the mediumwave band.

Here in the far American West, there are some big boys still transmitting IBOC. Notably, the strongest received in southwestern Arizona at night is Salt Lake City's 50 KW KSL-1160, followed by Los Angeles's 50 KW KNX-1070.

Adjacent to KNX-1070 on its upper side is 50 KW KRLD-1080 in Dallas, Texas. A two tower array with 4.8 dB gain in my direction pushes a respectable 150 KW effective radiated power (ERP) at me. KRLD-1080 is essentially impossible to hear when KNX-1070 is faded up to full strength as digital hash blankets 1080 KHz. Careful nulling of the radio's loopstick does help, but the two stations are nearly 180 degrees opposed to each other.

I mentioned that some radios are better than others in reducing adjacent-channel hash, not withstanding the nulling technique. In my stable of super portables, the Sangean ATS-909X does the best job, followed by the Tecsun PL-880 and the C.Crane EP Radio Pro. The difference in the Sangean is fairly remarkable, I believe owing to the Silicon Labs Si4734/35 DSP chip being used down-chain in the I.F., and the outstanding fidelity of the audio section.

The worst IBOC offender here is Utah's KSL-1160 at 506 miles distant. I am in its sweet spot, propagation-wise. Its 455 ft., half wavelength (+) single tower with gain of 2.31 dB pumps about 85 KW ERP at my direction. KNX-1070 has an almost identical tower, however at only 237 miles distant I am in its skip zone and thankfully much of its signal is wasted overhead in the E-layer on its way to New Mexico and beyond.

My best chance at reception on 1170 KHz, adjacent to KSL-1160 is Tulsa, Oklahoma's 50 KW KFAQ-1170. But it's a long way off at 1057 miles and it takes some tremendous power to overcome KSL's signal. As luck would have it, the three tower array's main lobe is pointed directly at me in western Arizona. With respectable 5.56 dB gain, it pushes an astounding 179 KW ERP at me. KFAQ-1170 should boom in here at night, but caught in KSL-1160's digital hash on 1170 KHz, it barely makes a dent unless KSL is in deep fade. If KFAQ fades up as KSL fades down it makes an appearance. WBAP-820, a 50 KW station also in Dallas and clear of an IBOC hash problem, is in regularly. So is 50 KW WOAI-1200 in San Antonio.

Shown in the graphic is KSL's received signal in my SDRPlay RSP1a SDR receiver's waterfall. As you can see, the sidebands creep well into the adjacent channels 1150 and 1170 KHz. My guess is they are pushing the 5 KHz audio bandwidth, causing needless and excessive digital hash, that, or over-compressing the audio, or both.

We will see in the future where digital will go in the U.S. mediumwave band.

Click image for larger version.

KSL-1160 Salt Lake City, Utah