"IBOC at Night, Five Years Later"

[Geographer]

When WLW was running IBOC, their analog signal sounded worse as you got close to the tower. When I parked at a restaurant adjacent to the tower, the whooshing sound completely obliterated their analog signal. As you got further from their tower, the whooshing sound disappeared but their audio sounded poorly modulated.

 

[Ai4i]

I remember getting what appeared to be a decent stereo receiver home (some Japanese model) to replace a failing older unit in the late 70's early 80's, and discovering that the AM tuner section was completely EQ'd for spoken word. Great crispness at around three kilohertz, but no lows or highs.

 

[audioguy]

One of my favorite programs over the years has always been "Music and the Spoken Word" featuring the Mormon Tabernacle Choir. KMOX has broadcast this program for many years and I have frequently listened to it over that station. However, since they chose to implement HD AM, reception has been vastly degraded.

Listening to the broadcast early this morning, I am increasingly convinced that the problem is not that the signal is weaker with HD transmission, it's a matter of self interference. The amount of hiss from the digital sidebands was so strong that at best, I would estimate that the S/N ratio was only 10 dB. Even using an analog tuned radio, it is very hard to tune so as to reduce the level of hiss to an acceptable level.

I don't understand why anyone in their right mind would damage their own coverage, let alone cause interference to stations on nearby frequencies for thousands of miles. HD AM is the dumbest idea ever.

Fortunately, I discovered that the program is actually available in the Chicago area on FM, so I'll be listening to it that way in the future. Too bad, though.

 

[kenglish]

Sounded fine leaving here (Salt Lake City) ;D .
(I'll pass your comments along, though. I assume you're listening to a CBS affiliate feed, not a Bonneville syndication feed.)

 

[audioguy]

Yes, I have heard the program before on FM over WAUS (Berrien Springs), which is the classical station that serves the area where my summer cottage is located. It sounds great on FM! It used to sound very good over KMOX before they went HD.

If you are involved in producing that program at KSL, please accept my sincere thanks. It is really one of the best programs left on broadcast radio. Incidentally I used to enjoy listening to KSL in SW Michigan before the FCC junked up the clears.

P.S. I did pick up the stream from BYU TV later this morning over the Internet and it sounded great. For some reason, though, there was excessive delay between the picture and the sound and I couldn't really stand to look at it during the spoken word parts so I just listened. But the audio and video quality were excellent otherwise.

 

[kenglish]

I've passed this thread along to Bonneville and to KSL-Radio.

Curious about what you use to listen to it....I suspect that the amount of "self-noise" depends on the bandwidth of the particular receiver. Also, the dynamic range of the musical program allows you to hear some of the interference, too...more so that with heavily processed programming at other times.

I might try listening to it on KSL-AM off-air, maybe even with the McKay-Dymek tuner. Can't get KMOX here .

 

[audioguy]

The radio I typically use at my bedside is a Sony SW11. Photo here: http://www.amazon.com/Sony-ICF-SW11-12-band-World-Radio/dp/B0002VM7MG. This is not a high fidelity radio, it is intended more for DXing and general purpose listening. However, the sound quality is not bad at all. It is much better than some of the DSP based radios I have used, which have very limited bandwidth and suffer from horrible pumping of the AGC system.

This radio has excellent sensitivity on the AM band and reasonably good selectivity. It can provide adjacent channel reception in most situations. For example, I can receive CBW from Winnipeg on 990 with a 50 kW Chicago station on 1,000 that is about 30 miles away from my location, but I have to null out AM 1,000.

However, I have many other radios and I have observed the IBOC on channel (self-noise) problem on all of them. I hope KSL sounds better than KMOX!

 

[DavidEduardo]

AM music sounds really good on all recently designed radios. By recently designed, I mean within the past 15 to 20 years. Another piece of iBiquity misinformation / outright lies was their contention that AM radios are limited to 3 to 4 kHz response.

Actually, the data came from an NRSC workgroup headed by Bob Orban. The group purchased a variety of current production model radios and measured the response; it was determined that the best AM bandwidth was around 6 kHz (the bandwidth many HD AM stations have adjusted for today).

The study also concluded that the receivers, as a group, rolled off severely over 4 kHz.

 

[diymedia]

AM music sounds really good on all recently designed radios. By recently designed, I mean within the past 15 to 20 years. Another piece of iBiquity misinformation / outright lies was their contention that AM radios are limited to 3 to 4 kHz response.

Actually, the data came from an NRSC workgroup headed by Bob Orban. The group purchased a variety of current production model radios and measured the response; it was determined that the best AM bandwidth was around 6 kHz (the bandwidth many HD AM stations have adjusted for today).

The study also concluded that the receivers, as a group, rolled off severely over 4 kHz.

Has this study been published anywhere?

 

[rbrucecarter5]

AM music sounds really good on all recently designed radios. By recently designed, I mean within the past 15 to 20 years. Another piece of iBiquity misinformation / outright lies was their contention that AM radios are limited to 3 to 4 kHz response.

Actually, the data came from an NRSC workgroup headed by Bob Orban. The group purchased a variety of current production model radios and measured the response; it was determined that the best AM bandwidth was around 6 kHz (the bandwidth many HD AM stations have adjusted for today).

The study also concluded that the receivers, as a group, rolled off severely over 4 kHz.

I don't see how you could even buy AM radios with the old "all American 6" transistor design with 3 IF coils. Unless you go to thrift shops and garage sales or something. I needed a replacement IF transformer a year ago, and tried in vain to find one. After buying three or four bargain radios - all, as in ALL were Sanyo or some other IC based, one ceramic filter AM, very wide audio response. I am sorry to have to say this, but I think Bob Orban purposely skewed the results by carefully researching which few of the existing production radios used the 45 year old reference design - probably to support a result greatly desired by iBiquity. It would not be first time a respected engineer followed the money or was intimidated into submission. I would say a 35 year old reference design, but by 35 years ago, ceramic filters were already making inroads and few radios had more than two IF cans. Most had two IF cans, making wider response than the old three can approach at the expense of a few images on the radio, forcing even more radios to include the IF can with the ceramic element inside. Radio Shack was always a bit ahead of the curve, they downsized the IF can count in the late 60's, two was standard in their gear into the mid 80's when they, too, started using ceramic filters. GE and Sony were the last holdouts on the traditional IF can designs, but even they succumbed to the pressure - with Sony using their proprietary CX1129 chip and GE getting out of the market.

Current production Sony based on their IC with 50 kHz AM IF are about the only narrow IF response AM radios on the market. Everything else has Sanyo or some derivation, one ceramic filter (if you are lucky), tiny ferrite bar or ridiculously small loop. Silicon Labs has chips that digitally sample the AM band, and have reasonable audio response. They are a little expensive, though, and not that common. Even digitally tuned radios use a two IC design, one to generate tuning voltage for varactors, the other the same old radio on a chip as everybody else. iHome docking stations are a good example. If by some miracle they made the IF narrower, the radios would be impossible to align because a 3 to 4 kHz mistake in the tuning somewhere on the band would mean they couldn't tune all stations. So they HAVE to be wide band to accommodate the sloppy tuning voltage generator IC. Very high end AM radio sections may add one IF can in addition to the ceramic filter, and it makes a huge difference to the noise floor of the receiver. But they are still way wider than 6 kHz audio response. If the radios are narrow audio response, it is done with high and low pass filters in the audio section to equalize the radio for talk and sports - not the IF where it would help clean up IBOC artifacts. So - yes - where did Bob find the antiques???? Sure was in iBiquity's best interest. I'd sure like to see his list of radios, because they would be a gallery of antiques in all likelihood.

Don't believe me? Go buy an "all American 6" transistor based design with three IF cans, or even an IC based radio with three IF cans and tell me the manufacturer and model. Good luck with that!

 

[DavidEduardo]

AM music sounds really good on all recently designed radios. By recently designed, I mean within the past 15 to 20 years. Another piece of iBiquity misinformation / outright lies was their contention that AM radios are limited to 3 to 4 kHz response.

Actually, the data came from an NRSC workgroup headed by Bob Orban. The group purchased a variety of current production model radios and measured the response; it was determined that the best AM bandwidth was around 6 kHz (the bandwidth many HD AM stations have adjusted for today).

The study also concluded that the receivers, as a group, rolled off severely over 4 kHz.

Has this study been published anywhere?

It's an NRSC paper. Should be available. It was widely written up in the trades, too.

 

[kenglish]

http://www.nrscstandards.org/Reports/NRSC-R101.pdf

 

[rbrucecarter5]

http://www.nrscstandards.org/Reports/NRSC-R101.pdf

Just a few pages? And a few of the models were listed, but no comprehensive list of what receivers were actually measured, no attempt to differentiate between whether the audio roll off was done in the IF or audio sections (which makes a HUGE difference to selectivity), their pulsed modulated first adjacent interferer was at least an attempt, but doesn't measure true selectivity. The link to the full report is broken. A careful researcher would have included schematics of all 30 models, plus photographs of the circuit boards - then estimated the theoretical bandwidths of each model to compare with the measured results. Bandwidths would have been measured at the line out of the receivers or across the volume controls to bypass as much of the audio section as possible. What is relevant to IBOC is the IF bandwidth of the receiver, not the audio response at the speaker, because IF bandwidth is what would make or break the AM IBOC system.

"and with the understanding that most consumer receivers are band limited to 5 kHz or less" - conclusion reached before they ever started their test. As I have indicated - this is a false assumption.

All warning signs to me that the results are not scientific, and slanted to support a particular conclusion. The date of the report - 2006 - is very much "after the fact" - a study like this should have been done a decade earlier, before the IBOC for AM was proposed.

 

[satech]

All warning signs to me that the results are not scientific, and slanted to support a particular conclusion. The date of the report - 2006 - is very much "after the fact" - a study like this should have been done a decade earlier, before the IBOC for AM was proposed.

The entire AM IBOC system was based on the preconception that nobody would care if the analog bandwidth was reduced to 5 kHz. In fact, in one of Ibiquity's own tests of AM receiver audio response, all the graphs showed a mysterious sharp dropoff in response at 5 kHz. Only buried in fine print in the footnotes was it mentioned that the transmitter used for the test was transmitting an IBOC signal with the analog audio restricted to 5 kHz! But yet they tested the receiver reponse up to 10 kHz anyway, even though everything above 5 kHz was just noise from the IBOC digital sidebands and was completely irrelevant!

 

[rbrucecarter5]

http://www.nrscstandards.org/Reports/NRSC-R101.pdf

http://earmark.net/gesr/Current_Radio_Design.htm

Here is my analysis of the circuitry inside probably 95% of all radios. Hardly narrow band.