HD (IBOC) on AM, Short Band Scan

[Steve - WB3HUZ]

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...

[WA3VJB]

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

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

[Bill, KD0HG]

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.

[k3zrf]

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.

[John K5PRO]

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. 

[John K5PRO]

"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.

[Tom W2ILA]

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

[Steve - WB3HUZ]

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

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.

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

[flintstone mop]

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

[WA3VJB]

through a 100mw transmitter in the house.  100Mw straps.

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

[KC4KFC]

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.

[Carl WA1KPD]

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

[k4kyv]

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.

[Bill, KD0HG]

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

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.

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

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

[k4kyv]

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?

[NE4AM]

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...

[2ZE]

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.

[Bill, KD0HG]

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?

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.

[KC4KFC]

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.

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

[Steve - WB3HUZ]

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?

[WA3VJB]

... 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

[Steve - WB3HUZ]

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

[WA3VJB]

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

[John K5PRO]

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.

[Bill, KD0HG]

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.