The AM Forum

Hooked the Boston Acoustics HD receiver to the 75 Meter dipole earlier today to give a listen to some AM broadcast stations running HD/IBOC.  Identified the following stations running HD.

570    WTNT   Washington, DC
630    WMAL   Washington, DC
910    WRNL   Richmond, VA
980    WTEM   Washington, DC
1140  WRVA   Richmond, VA

The receiver would not lock up for HD on the Washington, DC stations. WRVA locked up easily but WRNL lost lock every so often.

The audio had quite a bit more high frequency response on HD as compared to analog. However, it did not have a whole lot more than a well set up station received on a wideband receiver, like a SP-200 or similar with 16 kc plus IF bandwidth.

The SNR was improved when the HD locked up. But WRVA is pretty strapping here, so the SNR is good even in the analog mode. It would have been interesting if some of the Washington, DC stations would have locked up, since the SNR on those stations was much lower than WRVA.

I want to listen some more to get some different programming/origination, but what I heard was comparable to a low data-rate streaming audio source on the Internet. As I mentioned previously, the high frequencies were more prevalent in HD, but they were a little harsh.

I also want to see what's out there during the night hours, now that the FCC has approved HD operation at night.

More later...

I remember when the "AM Stereo" marketing campaign was rolled out, some saw it as a chance to finally get the receiver manufacturers to improve their AM sections as long as they were at it in adding the feature.  That didn't happen.

Here, your summary may preview that HD IBOC on AM is again a chance to try to get manufacturers to improve the fidelity of some of the spectrum their radios receive, as long as they are at it in adding a capability.

The problem is that, compared to bringing in AM Stereo, this time there really isn't any connection to "AM" when IBOC digital circuitry is added. They could still neglect the analog portion of their receiver even when tuning the same part of the band.

We shall see.

I wonder if anyone on here has done some nighttime IBOC reception on the AM band to see how many analog stations are wiped out by the digital trash on channels nearby.

In the design standards, approved by the FCC, stations can run their telemetry bandwidth out to as far as 15Kc from their center frequency.  Wouldn't that have been nice for good old analog frequency response? Wow.

"ERRR, your 30kc WIIIIDE old man !!!!"""

Anyway, here's a running list that a guy is keeping, with links to regulatory background information.

---

^{tnx, Barry McLarnon VE3JF}

http://topazdesigns.com/iboc/station-list.html (http://topazdesigns.com/iboc/station-list.html)

This was the weekend stations on the Standard Broadcast band were allowed to begin transmitting digital at night, instead of limiting such interference to daytime hours on groundwave.

(http://topazdesigns.com/iboc/AM-IBOC-Spectrum-v3.jpg)
http://topazdesigns.com/iboc/AM-IBOC-Spectrum-v3.jpg (http://topazdesigns.com/iboc/AM-IBOC-Spectrum-v3.jpg)

I listened on Thursday night. I was able to get a digital lock on several out of town stations, WGN 720, WLW 700, WHO Des Moines on 1040 and KMOX St. Louis on 1120.

That's really cool, was unaware that digi AM/FM was happening. New SWL horizons.

What's out there for receivers? I see the ref for Boston Accs.

I don't have an HD receiver, shoot, i don't even have HD television out here in the sticks. However, I did tune the NRD535/D around the MW band last night and again early this morning. I heard some interference to skywave signals from adjacent channel IBOC transmissions, sounding like either white noise or a strange gurgling "hash" depending on fades. Here is what I posted to the Broadcast forum:

"Tonight I finally had time to listen, first while driving home with a Monsoon stereo, then listened to Japan Radio Corp NRD-535D at home. Neither has IBOC decoding. What I recognized of iboc noise here in Santa Fe County, NM is listed below. I know, i know, I am not local to any of these and DX doesn't count anymore:
870   some background hash, talk radio overrides it
1030 nearly 100% digital noise
1050 mostly noise
1060 talk radio, >50% noise on top
1070 KNX clear
1080 noise on top of KRLD
1100 nearly 100% hash
1110 KFAB nice and clear
1120 nearly 100% hash (prob KFAB)
1190 nearly 100% noise from 1200
1200 clear
1210 KGYN getting wiped from upper side of 1200. 

"That's really cool, was unaware that digi AM/FM was happening. New SWL horizons.
What's out there for receivers? I see the ref for Boston Accs. "

Look at the past six months backissues of Radio World magazine, online. You can find many discussions and reviews of receivers. Not too many yet, that would be considered SWL-feature boxes. The problem with this new mode (in-band on-channel digital) is that it is operating in a compatability mode which allows analog AM as we know it here, to be transmitted, along with the digital sidebands. This is the crux of the problem, as these are digital noise which, grow in amplitude if the station has difficulty meeting certain antenna pattern bandwidth and transmitter specifications. During the daytime, its a no-brainer, as there is usually adequate spacing between local stations. Also, stations may be operating non-directional with better control of their antenna VSWR bandwidth. During nighttime, which was just allowed iboc operation, starting on Friday at midnight, many stations operate into directional antenna arrays, which are much different than their NDs. The skywave, which we all cherish here, is bringing these obnoxious sidebands back down on the adjacent channel stations. The premise from FCC and proponents of the systems) is that nighttime radio should no longer rely on long-distance skywave propagation. This means that trying for DX via the analog mode, may become futile. End of the clear channels as we knew them.

I just scored a 1989 Delco AM stereo from a junker for my 1989 s-10. 
I don't think they ever had an IBOC option when they discontinued the design in 1994.  I'm stuck listening to AM Stereo and CR02 tapes with Dolby.  Still can't hear above 1600.
It seems that the IBOC stations are really tearing up my SX62 listening pleasure too so now most AM programming is via internet and being broadcast through a 100mw transmitter in the house.  100Mw straps.

ILA

Dave - check out some of the Sangean offerings for HD. The Boston Acoustics rx is no longer sold, if I have my info correct.


Cool. What sort of improvement (if any) in reception did you hear on HD compared to the analog reception?

There are a lot of very unhappy people that cannot listen to their favorite out of town AM programs thanks to the broad hissing sound (30khz) of IBOC. The AM band has been trashed and will never recover!!
Fred

Isn't that the kind the real estate agents use ?

I read somewhere that the Boston Acoustics had a very poor front end and that several of the new HD receivers are the same.  The Sangean HDT-1x seems to be getting good reviews and I wonder about it's sensitivity.

I tuned across the AM band Sunday night and heard WGN WLS WBBM and many more stations with an old Blaupunkt Sultan with  a Radio Shack indoor loop (9" or so) inductively coupled. (I had to prop it up against the back of the set where the poor short ferrite antenna would hear it.) This is south of Nashville. I have just aligned the set and I thought it did pretty good.

I didn't hear huge interference or digital hash that I could readily call IBOC interference. OTH I am not an every night BCB DX'er.

I wonder if anyone can comment on the sensitivity of these HD sets and what kind of signal does it take for these stations to lock onto digital.

I heard it in the car last night. I was listening to the big Hartford station WTIC 1080. In the general Hartford area the has wiped out 1060-1100. It was a mess. However once i got about 15 air miles from the antenna I was able to listen to WBAL in Baltimore on 1090.

I want to listen from the shack and see what the hash is like from there and see if I can hear the hash on DX stations

I tuned across the AMBC band the other night.  It didn't seem too different from usual with the R-1000 using a few feet of wire for an indoor antenna.

With the 75A-4, which tunes down to about 1480 on the 160m band position, I noticed what seemed to be unusually loud hiss between signals, using the 160m beverage antenna.

I could copy CJBC, Toronto on 860 fairly well when the nighttime competition would fade down.  I could still hear the clear channels on 1000 and 1010.

But it is hard to tell with QRN in the background and the indoor antenna was picking up some electrical noise as well.  If there is a big difference, it will show up under quiet winter condx.

When I worked as broadcast engineer back in the mid 60's, our transmitter ran wide open audio response.  Our proofs always showed flat response, within a couple of dB's out to 15,000~.  With music, the signal would occupy the full 30 kc/s channel. But IBOC hash is undoubtedly much more destructive than the normal upper audio frequency components of analogue sidebands.

I'm afraid IBOC has line noise on its side.  I don't think too many members of the general listening public try to pull in weak distant AM signals due to local electromagnetic pollution, so they wouldn't notice the hash on the stations that are strong enough that they would even bother to listen to, to begin with.  Therefore there will be a very limited number of complaints from the general public.   

I can get the NPR AM signal from Nashville on 1430 pretty well here at the house.  But when I try to listen to it in the car, about 50% of the time the signal is unlistenable due to the shitty power lines running along the side of the road.  Of course, its signal completely disappears into the crud at night, even though they transmit 24/7 @ 10 kw.

Steve:

On the AM band, a signal needs to be strapping before you can get a good digital lock since the digital sidebands are weaker than the analog signal to begin with.

But it's pretty cool to hear an AM DX station suddenly blend into 100% noise-free hi-fi stereo. It's like- WHOA!

KMOX does a weekend jazz show at nite and I can't wait to try catching it in digital mode.

The thing is, the digital-capable receivers are much superior performers even on analog than the cr@p receivers they've been foisting on the public over the last 10 or 20 years. They have to be.

Sony just came out with a table-top AM receiver that seems to be getting rave reviews for performance.

http://www.crutchfield.com/S-HhnH9hnVu7N/cgi-bin/ProdView.asp?search=sony+hd+radio&i=158XDRS3HD

Are the digital sidebands symmetrical, that is, generated by simply modulating a conventional AM transmitter with with digital data converted to the 5-15 kHz range, or are the digital sidebands generated with a separate ISB process, so that there is different data in USB and LSB?

Back in the AM Stereo days, the Chrysler receivers all used the same board, just assembled differently for the different receiver versions.  AM Stereo was enabled with the addition of about 50 cents worth of parts.  In the mid 90's they stopped making the AM stereo versions of the receivers, as they felt the ability to receive AM stereo was not worth the extra 50 cents to the consumer!

I KNOW IBOC reception costs a lot more than 50 cents to implement - we'll just see how long the automakers offer HD as an option...

Don,
the digital carriers are symettrical. Someone asked if the Sangean HDTX-1 was any better. It's funny you mention that... When I was down there at iBiquity, a tech had one on the bench puttin' it through its paces. I asked what he had and he told me, then I asked if it was any better than the BA rx. His response was " by miles". I have not listened to it, but I imagine it isn't as deaf as the BA is.
I just read the review about the Sony, and the Radiosophy. The Radiosophy has a better front end than the BA and the Accurian (Rat shack),supports RDS and is under 100 bux. When I start, I'll have them buy me one and see for myself. ;)

Don:

No, it's not ISB, your first assumption is the more correct one.

The simple answer is that to convert an AM transmitter to hybrid IBOC operation, a new exciter is needed which does the encoding. The exciter has an audio input (Stereo AES/EBU) and two outputs that feed the AM transmitter:

One is the RF output which is the AM carrier (feeds the crystal input of the transmitter) that is a phase reference, the other output is wideband audio, which feeds the audio input of the AM transmitter. The IBOC audio signal modulates the AM transmitter. Part of this composite audio is conventional AM-quality audio, which the analog receivers work on. The expanded part of the audio creates the digital sidebands.

So what you're doing is feeding an AM transmitter with very wideband audio. The transmitter needs to have (if I remember correctly) flat audio response and minimal phase shift out to ~25 KHz. By and large, our heavy iron broadcast transmitters can't cut it. The newer PDM tube and digitally-modulated solid-state AM boxes can be made to work with some mods to open up the audio response. The latest AM boxes are ready to go, you need to change their audio bandwidth setting and plug in your new IBOC exciter. Bingo.

The digital information is carried as a quadrature-modulated component of the AM carrier.

Actually, HD is similar in implementing to the old AM C-Quam system.

Hi Don,   I have exactly the same experience with 1430 kc south of Nashville. I regularly listen to 1430 here five miles east of Fairview. I am surprised to hear it as well as I do with an indoor antenna. I think the tower is in Madison?  The power lines here are also very bad along Highway 100 but Williamson County Electric did substantially reduce the loud noise on the transformer just outside my house.

If I could receive 1430 digitally with FM quality, I would buy an HD receiver. ( I am thinking the Sangean HDT-1x because you can toggle between analog and digital.) I just have no idea if the signal is strong enough.  I guess Signal to Noise ratio is the criteria?  If I can lock onto DX, then that would be a plus. KMOX is usually strong here.  I don't listen to FM except for WPLN (Classical and NPR) and WMOT (Jazz) but HD2 alternatives might be interesting.

Someone mentioned the quality as being like low-bit rate streaming. That is not CD quality. Is it that bad?

Oh yes, I also like 1200 kc WAMB (Big Band) which actually is weaker here than 1430 even though I think closer. Is 1200 broadcasting HD?

So, I may actually listen to radio more because of IBOC. ( I just will have to run it through a tube amp so it sounds good.)

KC4KFC     Mark

The Boston Acoustics receiver is pretty deaf - on AM and FM. I also got some intermod/crossmod when I hooked it up to my 75 meter dipole. It's good to hear that some of the newer receivers are better in these areas.

I've heard the jazz on KMOX Bill. Sounds pretty good on analog when KMOX is strapping here. It does get whacked by WBBR on 1130 out of NYC since BBN really straps into this location (it even blasts the local 50 kW strapper, WRVA on 1140 sometimes, like early evening). WBT out of Charlotte on 1110 also straps in here at night and puts some slop on KMOX. But if HD will lock up, all that should go away.

I hope to test out the Sangean HDT-1X soon. It supposedly has a sync detector and variable bandwidth on the analog side, which should also be fun to play with too. Wonder why few, if any receivers had this before?

Damn few have had selectable bandwidth AND synchronous detection.
I can think of two:

The Sony 2010 and the Grundig Satellit 800

And those were shortwave receiver. The Sangean is just for the AM BC band.

Kevin Tekel posted this to a broadcast reflector, where there's a similar thread underway regarding IBOC on the AM Band.

Okay, you made me drag out and dust off my cassette collection to dig
 up
this one... it's an aircheck of the dearly departed 1190 WOWO via
 skywave
in full C-Quam AM Stereo, from November 1992, with adjacent-channel
interference audible, presumably from 1180 WHAM (the recording was made
 in
eastern Pennsylvania on a Realistic TM-152).  In this clip, WHAM was
 near
its peak strength, and you hear WOWO finishing a song while WHAM has
 some
sort of talk programming... then both stations hit their legal ID
 jingles
and join CBS News at the top of the hour exactly in synch:

http://mysite.verizon.net/tekel/wowoclip.wav

I posted it as an uncompressed WAV so you have the best quality to work
with... now let's see if you can extract WHAM and make their legal ID
intelligible!

Photo courtesy of:

http://ourworld.compuserve.com/homepages/kevtronics/history.htm (http://ourworld.compuserve.com/homepages/kevtronics/history.htm)

(http://ourworld.compuserve.com/homepages/kevtronics/tm152.jpg)

My JRC NRD-535/D has synchronous detection with selectable upper or lower sideband cancellation, and variable BW. The synch detector does loose lock if two stations are far apart in freq, more than a few hundred Hz though. It reverts to envelope det mode then.

I have one of those old Rat Shack AM Stereo RX too! And the original Sony portable AM stereo SRFA100, which had a mode switch for Motorola, Harris, Magnavox or Kahn system. It still plays well, although the FM on it is horrible.

I have to suggest holding off on any HD radio purchase right now, until early next year.

Ibquity and Samsung are releasing the latest HD chipset in the near future, which I think would perform better.

The current chipset is a couple of years old and uses something like 4 watts. The new one reportedly uses 1/10 that much power.

Beyond that, they've had a few years to improve the design and decoding.

I would wait until next year until receivers based on the new chips are available. You'll know that when HD capability starts showing up in portable equipment like radio headsets and Walkman.

Honestly, HD was never intended to be a DXers mode, it depends on a decent, stable signal to work properly. That means the receivers themselves are way above average AM BCB performers, even for analog reception, with well-designed front ends and real IF filters. A lot of selective fading with it's phase-shifting murders the digital decoders, from my experience. I am optimistic that the new chips will offer improved performance, so that's why I say to hold off a few months if you want the latest and best performance.

Interesting link here, to report the skywave interference to AM broadcasters. The big boyz just don't want to hear it if you tell them that so and so is being clobbered by QRM at night, when you are listening to their skywave. Heck, thats ALL we hams listen to, for the most part!

http://www.hfunderground.com/wiki/Reporting_Interference

Start to what? Low bit-rate, high drop-out subscription radio over public airwaves? Great! sign me up!

Huh?

On FM, 96K minimum bitrate, more than twice that of a CD.
Even if split into two programs, it's darn near CD quality at 48K per stereo channel. Sound quality is awesome.

AM HD sounds very, very good.

Have you ever heard an HD radio?

I think he means like those free subscriptions to the public airwaves given by XM and Sirrius and all the cell phone companies.

I tried to listen to an HD radio, but no one around here carries any. I really would like to hear one hooked up to a good set of speakers and compare to regular FM.

From what Ive been reading, these signals are highly compressed, and get "muddled" from all that alogarhythmic malarky. Also, the bitrate is starting around 48 bps and will probably be lower depending on how many channels the broadcaster wants to cram into the bandwidth. I like listening to FM, the music sounds pretty good and I have a critical ear. The last thing I want to hear is a warbling  watery sound.

As far as IBOC AM goes, I can just imagine what happens when you go under a high line and lose that strong signal that is needed. Once the tower pops back behind a hill, then bye-bye IBOC. Did anyone mention the 8 second delay? Im sure that will work great when listening down at the ballpark.

This is from : http://electronics.howstuffworks.com/hd-radio1.htm

HD Radio solves this problem by compressing the digital signal so more information can be sent along the same amount of radio bandwidth. Initially, iBiquity used a compression algorhythm called PAC (Perceptual Audio Coding). However, audio compressed with this method led to complaints about poor sound quality, so in 2003, iBiquity changed to HDC (High-Definition Coding), a different compression method that allowed for higher sound quality.

Although HD Radio is touted as providing CD-quality sound on the FM airwaves, the compression of the digital signal is a "lossy" method. That means that it discards some of the information in the signal, resulting in a reduction in overall fidelity to the original sound. Much of the discarded information is not perceptible to human ears, and the final product may sound very close to CD-quality, but technically it is not the same sound as on the CD.

Having listened to HD stations, both AM and FM, I've never heard watery audio, warbling audio, or anything approaching an 8 second delay.

CD quality is more than just bit rates and compression issues. SNR and dynamic range are just as important and NO AM or FM station will yield an SNR capable of supporting the same dynamic range as a CD. Not even close. Having listened to FM HD stations, the thing most immediately noticeable to my ear when the receiver switched from analog to HD was the big reduction in noise. From this, it would seem HD/IBOC would be far closer to CD sound than analog FM.

There are many places that carry HD Radio: Best buy, circuit city, even Rat shack and Wal-mart.

As far as watery sound....
Better give a listen before you criticize. But by the sounds of things, you and all of the other so called experts have already made up your mind. All I ask is you don't poison other peoples opinion who may have not tried it yet.

As far as subscription service, the technology is there, however, even big box corporate owners dont have/want the resources to be in the subscription biz. Every station would now have to maintain/ service up to tens of thousands of accounts? I don't think so. Broadcasters will stick to what they do best, being broadcasters.
Mike, 2ZE

Finally got a chance to mess with the Sangean HDT-1X. This radio is WAY more sensitive than the Boston Acoustics unit -  both on AM and FM.

One FM, using the folded dipole supplied with the unit tacked to the wall of my basement, I was able to receive dozens of FM stations, easily as many as I would expect with an FM receiver with good sensitivity. I don't think I received this many FM stations with Boston Acoustics unit using an outdoor antenna! The following HD stations were received and decoded.

WHRV     89.5     Also broadcasting a second digital channel
WRVQ     94.5     Also broadcasting a second digital channel
WVKL     95.7
WKLR     96.5
WRXL     102.1    Also broadcasting a second digital channel
WMXB    103.7
WAFX     106.7

Several of the stations were a little noisy in the analog mode. The noise completely disappeared when the HD locked up. Much improved sound on all the station with more high-frequency response, less noise and better stereo separation.

On AM the sensitivity was very good. I hooked the receiver to my 75 meter dipole and was able to pull in a station on almost every channel during day light hours. Audio response was very nice, although I didn't hear a much high frequency response as I would on my SX-17 in the Broad Selectivity mode. I did not find any control to vary the bandwidth, nor did I notice any documentation of the synchronous detector. Might have to try it on some stations at night with selective fading. I was able to receive the following HD stations.

WFAN     660
WCBS     880
WRNL     910     Stereo
WRVA     1140   Stereo

This receiver locks much better on AM stations than the Boston Acoustics unit. Note in the list above, I was able to lock on two stations out of New York City about 280 miles away! There was even some fading on WCBS.

Gonna try the AM Loop antenna supplied with the unit next. I'm guessing I won't get the NYC stations during daylight hours on it.  ;-)


Ref: http://amfone.net/Amforum/index.php?topic=12092.msg88021#msg88021

I haven't listened to the AM BCB for since before nightime IBOC got the FCC ok. A short scan of the band tonight from my locale in central MD:

WSM Nashville 650 wiped out by WFAN 660 NYC
WLW 700 Cincinatti wiped out by WOR 710 NYC
WBT 1110 Charlotte listenable, but under objectionable digital noise from 1100 WWWE Cleveland
WBBR 1130 NYC identifiable but lost under digital sidebands from station on 1120 (St. Louis?)

While I'm sympathetic to giving AM stations a crack at digital service, I think it should have been done on different spectrum. Perhaps the wasteland in the 25-27 MHz region, or higher on VHF Channel-2 when DTV cuts over in 2009. From my perspective at least half of the nighttime skywave service is now gone and the other half is polluted by digital tee-rash that makes listening unpleasant.

73, Jim
WA2AJM/3

I lose 650 WSM regularly to WFAN, 690 to 730 is mess of hiss down here, depending on the propagation, most nights WOR 710 covers WLW 700 and WGN 720, some nights WLW covers WOR, some nights all three cover each other. 780 WBBM also blocks 770 and 790 quite a bit. When WBZ 1030 is on at night forget it that's all I hear from 1010 to 1045.  WCBS 880 also blocks 870 and 890. There are some others that hiss up the band here also. At the bottom of this post is a link to a list of iBlock stations on both day and night. The list is not growing very fast in fact it shrank recently when Citadel shut it off due to consumer complaints.

Here's a column about Ford's new iBlock offer:

http://gormanmediablog.blogspot.com/2007/10/blog-post.html

here's something about when Citadel shut of their iBlock and why

http://www.orbitcast.com/archives/abc-citadel-suspends-am-iboc.html

here's all aM iBlock stations on the air, this is constantly updated:

http://topazdesigns.com/iboc/station-list.html