How well does HD AM decoding withstand dimmers?

[Tom Wells]

By far the ugliest and strongest noise most homes encounter is the dreaded ......

"Discontinuous Current Device" of various flavors, which switch on and off our AC loads so conveniently.

By "our" I mean "your" as I have taken multiple steps to keep my environment pure as possible.

Americans love the auto-on-at dusk lamp, the dimmer, the variable-speed fan, the pulse-ignition oven and furnace.
They love the switching mode power supply, the flourescent lamp, the computer, the video game, the vacuum, the hair-dryer,
the electric food mixer, coffee grinder, food processor, Ionic Breeze (tm), the television, (especially plasma), the digtal readout,
neon lights in the basement, UPS power supplies, power conditioners, bug zappers, cell phone chargers, cordless phones,
cable TV systems, microwave ovens, electronic furnace air cleaners, and may live nearby mains with similar
and even worse byproducts of noise from industrial drives, traffic signals, and poorly maintained AC distribution equipment.
Not to mention noise from your neighbors with the same conveniences as you.

Now, remembering that such triac/scr noise from dimmers completely swamps out regular analog reception.....

With such an onslaught of multiple RF hash within the home, particularly lamp dimmers, how well does HD AM recption fare?

I suspect few homes are pure enough for the HD sidebands not to be overshouted by the locally generated noise.

I eagerly await real-world testing by someone with both Accurian and "regular-house" noise levels.

And what about wood, vs steel or brick? Does steel framing make AM HD indoors impossible?

 

[Mike Walker]

I do as well!

There was an "ultimate AM receiver" (as I think it was called) demonstrated at the NAB Radio Show in 1995 that had noise blanking. In the demo you could hear how it almost completley ignored interference from things likd light dimmers and flourescent lights. Anyone else remember that? Of course it was an analog radio, but did seem to have a remarkable freedom from noise.

 

[R.F. Burns]

By far the ugliest and strongest noise most homes encounter is the dreaded ......

"Discontinuous Current Device" of various flavors, which switch on and off our AC loads so conveniently.

By "our" I mean "your" as I have taken multiple steps to keep my environment pure as possible.

Americans love the auto-on-at dusk lamp, the dimmer, the variable-speed fan, the pulse-ignition oven and furnace.
They love the switching mode power supply, the flourescent lamp, the computer, the video game, the vacuum, the hair-dryer,
the electric food mixer, coffee grinder, food processor, Ionic Breeze (tm), the television, (especially plasma), the digtal readout,
neon lights in the basement, UPS power supplies, power conditioners, bug zappers, cell phone chargers, cordless phones,
cable TV systems, microwave ovens, electronic furnace air cleaners, and may live nearby mains with similar
and even worse byproducts of noise from industrial drives, traffic signals, and poorly maintained AC distribution equipment.
Not to mention noise from your neighbors with the same conveniences as you.

Now, remembering that such triac/scr noise from dimmers completely swamps out regular analog reception.....

With such an onslaught of multiple RF hash within the home, particularly lamp dimmers, how well does HD AM recption fare?

I suspect few homes are pure enough for the HD sidebands not to be overshouted by the locally generated noise.

I eagerly await real-world testing by someone with both Accurian and "regular-house" noise levels.

And what about wood, vs steel or brick? Does steel framing make AM HD indoors impossible?

I can address this. I have heard analog AM filled with localy generated static switch to digial mode and the signal was pure and interference free. The reason is that if the data stream isn't too corrupted the radio only see's zero's and ones. It ignores the static.

 

[PhilJSmith67]

Re: How well does HD AM decoding withstand any RFI at all?

I don't have any triac-based dimmers, so I can't comment on how well the Sangean HDR-1 can withstand interference from them to AM HD Radio stations. I have always hated triac-based dimmers because of the unacceptable noise they spew from 200 kHz beyond 21 MHz.

As for lightning, I had my first experience with its effects on AM HD Radio reception Tuesday. I am highly disappointed with how easily the AM HD Radio bitstream is corrupted by low to moderate levels of lightning noise.

Tuesday morning there were storms about 40 miles distant. Static was audible on vacant frequencies, but it was not very strong nor frequent; I would hear a mild crackle every 10 to 20 seconds. On my local channels (WSCR, WGN, WBBM, WVON) with an analog Walkman, the crackle was low and very tolerable from a listenability perspective. There was no crackle at all on WLS.

When I flipped to any of these stations on the Sangean, which initially plays the analog signal, the audio sounded clean with very little crackle, just like the Walkman. However, the receiver was unable to remain locked on any HD Radio signals for hardly more than 10 seconds at a time. On 670 WSCR, 720 WGN, and 780 WBBM, the receiver spent far less time in digital mode than analog! WVON fared a little better, most likely because lightning static is attenuated more at 1690 kHz than the low end of the band.

The real kicker was 890 WLS. This 50k-watter is 19 miles from me, and sounded no different Tuesday than it would in the middle of winter, with a strong, clean, static-free signal. My Sangean HDR-1 normally shows a consistent 34.7dB signal on WLS, and the audio never skips a beat. On Tuesday, the HD Radio signal repeatedly dropped out every 20 seconds or so, for 5 to 8 seconds at a time. The signal meter spent most of its time showing 34.7dB, but would occasionally dip into the 31's or 32's, then immediately rebound to 34.7. Coincidentally, it would dip when I heard static on vacant channels on the Walkman, and very shortly after, the audio would revert to analog. However, the Walkman was also unable to "hear" any static on WLS itself.

My final test was the good ol' lightswitch, about 3 feet above the receiver. Tuned to WLS this morning (Wednesday) with no storms present, I saw the typical 34.7dB lock on the HD Radio signal. I flipped the lightswitch on, then off, then on, at approximately 2-second intervals. The Sangean lost lock on the HD signal with the first flick of the switch, and it remained unlocked as long as I kept up the routine. The signal meter dipped to 31 or 32 each time. Just like with the distant lightning, I was unable to hear any crackle at all from the lightswitch on analog WLS, yet it obliterated AM HD Radio reception. The higher-frequency 1690 WVON fared slightly better, remaining locked about half the time.

Based on this personal observation, I have to come to an unscientific conclusion that HD Radio on AM cannot deliver on the marketing literature behind it, which touts static-free, high-fidelity, stereo audio on AM. HD Radio was supposedly designed with OFDM modulation, trellis-encoding, and data redundancy to overcome these issues. After only one passing of a distant storm, I have found that HD Radio on AM is unacceptably fragile when faced with any transient noise. Did iBiquity or anyone else actually test this system in the presence of even a low or moderate level of transient interference? If not, that is a travesty. If so, that is an even greater travesty, because they would have had to ignore obviously unacceptable performance.

 

[SUPERCASTER]

Re: How well does HD AM decoding withstand any RFI at all?

I don't have any triac-based dimmers, so I can't comment on how well the Sangean HDR-1 can withstand interference from them to AM HD Radio stations. I have always hated triac-based dimmers because of the unacceptable noise they spew from 200 kHz beyond 21 MHz.

As for lightning, I had my first experience with its effects on AM HD Radio reception Tuesday. I am highly disappointed with how easily the AM HD Radio bitstream is corrupted by low to moderate levels of lightning noise.

Tuesday morning there were storms about 40 miles distant. Static was audible on vacant frequencies, but it was not very strong nor frequent; I would hear a mild crackle every 10 to 20 seconds. On my local channels (WSCR, WGN, WBBM, WVON) with an analog Walkman, the crackle was low and very tolerable from a listenability perspective. There was no crackle at all on WLS.

When I flipped to any of these stations on the Sangean, which initially plays the analog signal, the audio sounded clean with very little crackle, just like the Walkman. However, the receiver was unable to remain locked on any HD Radio signals for hardly more than 10 seconds at a time. On 670 WSCR, 720 WGN, and 780 WBBM, the receiver spent far less time in digital mode than analog! WVON fared a little better, most likely because lightning static is attenuated more at 1690 kHz than the low end of the band.

The real kicker was 890 WLS. This 50k-watter is 19 miles from me, and sounded no different Tuesday than it would in the middle of winter, with a strong, clean, static-free signal. My Sangean HDR-1 normally shows a consistent 34.7dB signal on WLS, and the audio never skips a beat. On Tuesday, the HD Radio signal repeatedly dropped out every 20 seconds or so, for 5 to 8 seconds at a time. The signal meter spent most of its time showing 34.7dB, but would occasionally dip into the 31's or 32's, then immediately rebound to 34.7. Coincidentally, it would dip when I heard static on vacant channels on the Walkman, and very shortly after, the audio would revert to analog. However, the Walkman was also unable to "hear" any static on WLS itself.

My final test was the good ol' lightswitch, about 3 feet above the receiver. Tuned to WLS this morning (Wednesday) with no storms present, I saw the typical 34.7dB lock on the HD Radio signal. I flipped the lightswitch on, then off, then on, at approximately 2-second intervals. The Sangean lost lock on the HD signal with the first flick of the switch, and it remained unlocked as long as I kept up the routine. The signal meter dipped to 31 or 32 each time. Just like with the distant lightning, I was unable to hear any crackle at all from the lightswitch on analog WLS, yet it obliterated AM HD Radio reception. The higher-frequency 1690 WVON fared slightly better, remaining locked about half the time.

Based on this personal observation, I have to come to an unscientific conclusion that HD Radio on AM cannot deliver on the marketing literature behind it, which touts static-free, high-fidelity, stereo audio on AM. HD Radio was supposedly designed with OFDM modulation, trellis-encoding, and data redundancy to overcome these issues. After only one passing of a distant storm, I have found that HD Radio on AM is unacceptably fragile when faced with any transient noise. Did iBiquity or anyone else actually test this system in the presence of even a low or moderate level of transient interference? If not, that is a travesty. If so, that is an even greater travesty, because they would have had to ignore obviously unacceptable performance.

Yes the "HD Radio Playbook" is a fantasy story filled with misleading hype and false advertising. Faithful HD supporters are deeply lost in denial.

 

[calstymes]

R.F. Burns clarified:

I have heard analog AM filled with locally generated static switch to digital mode and the signal was pure and interference free. The reason is that if the data stream isn't too corrupted the radio only sees zero's and ones. It ignores the static.

Quite true! Unless of course, the level of locally generated static (or noise) is too great and the data stream becomes "corrupted". In which case, the radio won't switch, eh? I have yet to have either of my two BA Receptors switch to a digital stream on AM in Manhattan except for very brief moments when the locally generated static and resulting S/N must not have been so bad.

I know, I know. My BA Receptors are and my neighborhood is flawed. I suspect that I will be using my BA Receptor's as doorstops soon. Possibly when I run out of doorstops. I guess I'll crank up the old Hammarlund and try and ignore the buzz.

 

[R.F. Burns]

R.F. Burns clarified:

I have heard analog AM filled with locally generated static switch to digital mode and the signal was pure and interference free. The reason is that if the data stream isn't too corrupted the radio only sees zero's and ones. It ignores the static.

Quite true! Unless of course, the level of locally generated static (or noise) is too great and the data stream becomes "corrupted". In which case, the radio won't switch, eh? I have yet to have either of my two BA Receptors switch to a digital stream on AM in Manhattan except for very brief moments when the locally generated static and resulting S/N must not have been so bad.

I know, I know. My BA Receptors are and my neighborhood is flawed. I suspect that I will be using my BA Receptor's as doorstops soon. Possibly when I run out of doorstops. I guess I'll crank up the old Hammarlund and try and ignore the buzz.

Of course under any circumstance there will be a level of noise which will make listening to any signal, analog or digital impossible. At work were we have our uplink dishes on the roof and ocasionally depending on the weather or other external events we experience something called TI (Terestral interference), which interupts the bitstream causing short term signal loss. These things happen (Only the downlink is actually effected). You've stated over and over that you have a few bad Receptors. You can't realy use a defective radio to make a judgement on how robust the digital stream is especially when the radio itself generates interference (The reason for the poor reception on your B.A.). I've lived with my HD radios long enough to have experienced lighnings effect on a good HD signal. With a proper meaning strong enough signal I didn't lose HD during a storm. If the signal is weak of course reception is lost.

 

[awj223]

This interference problem could very well be HD radio's downfall. I've said repeatedly that IF we are going to commit to the Ibiquity system for digital radio, we should move all stations to full digital ASAP, by FCC mandate, just like TV. Hybrid mode is inferior. The average person doesn't understand what "dB down" means and probably doesn't realize that the digital sidebands in hybrid mode are much weaker than the analog. To that person, HD radio technology itself is going to develop a bad reputation for itself.

Does anyone remember AT&T Wireless, the AT&T spinoff that ran itself into the ground and became an acquisition target for Cingular? (Cingular was part owned by SBC, which bought AT&T the parent company that spun off AT&T Wireless, and renamed both itself and its wireless division back to AT&T once it had acquired the naming rights. In any case, the new AT&T has no relation to the old AT&T Wireless). One of the major factors that contributed to its downfall was its botched rollout of a new technology. Mobile phones operate in two separate frequency bands in the US: 850 and 1900 MHz. AT&T Wireless had many markets running Digital AMPS (also known as TDMA) at 850 MHz. The base stations were spaced to provide coverage given the propagation of 850 MHz signals. 1900 was used as a fill-in frequency for capacity (those close enough to the towers could use it, but the network wasn't designed for optimal coverage at this frequency).

Around 2000-2001, AT&T Wireless made the decision to move from Digital AMPS to GSM, the standard that originated in Europe and was already in use in the US by Voicestream (now T-Mobile USA). Now, since none of the 850 MHz providers had been using GSM, GSM equipment that operated at 850 MHz was not available, but due to Voicestream's use of it, GSM 1900 equipment was already being sold. So AT&T Wireless decided to put GSM on 1900 MHz only at first, while they waited for GSM 850 equipment to hit the market.

That was a big mistake. With the network designed for 850 MHz, there were coverage holes everywhere. Customers who were being told that they were being "upgraded" to the "Next Generation" network, the early adopters most likely to spend lots of money on service, were rewarded with numerous coverage holes, dropped calls indoors, etc. Many went back to TDMA, and many switched providers. People developed the opinion that GSM technology itself was inferior, when in fact it was the use of a frequency that the network wasn't built for that was to blame for the problems. By 2003-2004, AT&T Wireless's stock price had dropped so low that it had become an acquisition target. Cingular on the other hand did a more aggressive rollout of GSM 850 since it also had a lot of 850 MHz optimized networks. No wonder Cingular did the buying and AT&T Wireless did the selling.

 

[R.F. Burns]

This interference problem could very well be HD radio's downfall. I've said repeatedly that IF we are going to commit to the Ibiquity system for digital radio, we should move all stations to full digital ASAP, by FCC mandate, just like TV. Hybrid mode is inferior. The average person doesn't understand what "dB down" means and probably doesn't realize that the digital sidebands in hybrid mode are much weaker than the analog. To that person, HD radio technology itself is going to develop a bad reputation for itself.

Does anyone remember AT&T Wireless, the AT&T spinoff that ran itself into the ground and became an acquisition target for Cingular? (Cingular was part owned by SBC, which bought AT&T the parent company that spun off AT&T Wireless, and renamed both itself and its wireless division back to AT&T once it had acquired the naming rights. In any case, the new AT&T has no relation to the old AT&T Wireless). One of the major factors that contributed to its downfall was its botched rollout of a new technology. Mobile phones operate in two separate frequency bands in the US: 850 and 1900 MHz. AT&T Wireless had many markets running Digital AMPS (also known as TDMA) at 850 MHz. The base stations were spaced to provide coverage given the propagation of 850 MHz signals. 1900 was used as a fill-in frequency for capacity (those close enough to the towers could use it, but the network wasn't designed for optimal coverage at this frequency).

Around 2000-2001, AT&T Wireless made the decision to move from Digital AMPS to GSM, the standard that originated in Europe and was already in use in the US by Voicestream (now T-Mobile USA). Now, since none of the 850 MHz providers had been using GSM, GSM equipment that operated at 850 MHz was not available, but due to Voicestream's use of it, GSM 1900 equipment was already being sold. So AT&T Wireless decided to put GSM on 1900 MHz only at first, while they waited for GSM 850 equipment to hit the market.

That was a big mistake. With the network designed for 850 MHz, there were coverage holes everywhere. Customers who were being told that they were being "upgraded" to the "Next Generation" network, the early adopters most likely to spend lots of money on service, were rewarded with numerous coverage holes, dropped calls indoors, etc. Many went back to TDMA, and many switched providers. People developed the opinion that GSM technology itself was inferior, when in fact it was the use of a frequency that the network wasn't built for that was to blame for the problems. By 2003-2004, AT&T Wireless's stock price had dropped so low that it had become an acquisition target. Cingular on the other hand did a more aggressive rollout of GSM 850 since it also had a lot of 850 MHz optimized networks. No wonder Cingular did the buying and AT&T Wireless did the selling.

But what you are overlooking is that while interference, whether it be locally generated or weather related effects every type of broadcasting. AM radio is filled with static making listening difficult if not impossible. rain and weather fronts will drop a sat TV signal to nothing. Duirng certain weather conditions sat TV just won't work. That's why I keep a terrestrial antenna as a backup. Still, that problem (and every subsccriber has loss of signal from time to time) hasn't dulled the number of DirecTV or Dish subscribers. FM radio in urban environments can be riddled with multipath. If it's bad enough the radio is unlistenable. What digital technology has over analog besides the ability to stream multple programs on a single frequency and conserve spectrum through compression techniques, is that as long as you are receiving the minimum amount of RF, your picture/slash audio is perfect. No ghosting or multipath and that is a major plus for the listener. The major problem they are going to have with cell delivered technology is first, it's far from seamless and second their inability to provide quality audio let alone video as the signal weakens. Sometimes there's so much compression employed over cell networks that understanding is dificult. In data terms that would me a slow thru-put whichis unacceptable for most entertainment purposes.

 

[awj223]

But what you are overlooking is that while interference, whether it be locally generated or weather related effects every type of broadcasting. AM radio is filled with static making listening difficult if not impossible. rain and weather fronts will drop a sat TV signal to nothing. Duirng certain weather conditions sat TV just won't work. That's why I keep a terrestrial antenna as a backup. Still, that problem (and every subsccriber has loss of signal from time to time) hasn't dulled the number of DirecTV or Dish subscribers. FM radio in urban environments can be riddled with multipath. If it's bad enough the radio is unlistenable. What digital technology has over analog besides the ability to stream multple programs on a single frequency and conserve spectrum through compression techniques, is that as long as you are receiving the minimum amount of RF, your picture/slash audio is perfect. No ghosting or multipath and that is a major plus for the listener. The major problem they are going to have with cell delivered technology is first, it's far from seamless and second their inability to provide quality audio let alone video as the signal weakens. Sometimes there's so much compression employed over cell networks that understanding is dificult. In data terms that would me a slow thru-put whichis unacceptable for most entertainment purposes.

What you seem to forget is that even digital isn't enough especially when the digital carriers are 20-30dB below the analog. Remember, HD radio is being sold as the solution to static, multipath, fading, dropouts, etc. You're correct that you have to be receiving at least a minimum amount of RF for digital to work. The reports I'm seeing seem to indicate that in its current inferior implementation, the digital signal is so weak that it drops out in areas where the analog is still listenable. This is a problem. That's why I think we either need full digital now or we just forget about IBOC.

 

[R.F. Burns]

But what you are overlooking is that while interference, whether it be locally generated or weather related effects every type of broadcasting. AM radio is filled with static making listening difficult if not impossible. rain and weather fronts will drop a sat TV signal to nothing. Duirng certain weather conditions sat TV just won't work. That's why I keep a terrestrial antenna as a backup. Still, that problem (and every subsccriber has loss of signal from time to time) hasn't dulled the number of DirecTV or Dish subscribers. FM radio in urban environments can be riddled with multipath. If it's bad enough the radio is unlistenable. What digital technology has over analog besides the ability to stream multple programs on a single frequency and conserve spectrum through compression techniques, is that as long as you are receiving the minimum amount of RF, your picture/slash audio is perfect. No ghosting or multipath and that is a major plus for the listener. The major problem they are going to have with cell delivered technology is first, it's far from seamless and second their inability to provide quality audio let alone video as the signal weakens. Sometimes there's so much compression employed over cell networks that understanding is dificult. In data terms that would me a slow thru-put whichis unacceptable for most entertainment purposes.

What you seem to forget is that even digital isn't enough especially when the digital carriers are 20-30dB below the analog. Remember, HD radio is being sold as the solution to static, multipath, fading, dropouts, etc. You're correct that you have to be receiving at least a minimum amount of RF for digital to work. The reports I'm seeing seem to indicate that in its current inferior implementation, the digital signal is so weak that it drops out in areas where the analog is still listenable. This is a problem. That's why I think we either need full digital now or we just forget about IBOC.

I don't know about you but I live 25 miles from modtown Manhattan where the FM transmitters are located. I consider 25 miles to be a suburb and I have no trouble receiving the HD stations (I've posted demos here). What I read is that people who are 60 miles from an HD station can't receive the HD. Well I've posted a HD station I receive on my Sangean tuner, but that said 60 miles away is not a suburb. 60 miles away is deep fringe. I other words it's outside of the market. I've driven 60 miles from the rransmitters in NYC. Sure the signal can be received but it's spotty at best. Forget power levels, hey with 100 watts or so I am able to hit a geostationary satellite with a solid signal, and that bird is some 20,000 miles away, above the Equator over Hawaii and that's a digital signal. Look at it this way, the diference in RF penetration between today's digital cell phones and the old analog ones is the difference between night and day. I remeber the days of analog mobile phones and on those the batteries lasted maybe 20 minutes and those batteries were relatively enormous. Today you can get more than 24 hours on a cell bettery. Digital is a much more efficiant method of transmission than analog. It's a simple as that.

 

[awj223]

I don't know about you but I live 25 miles from modtown Manhattan where the FM transmitters are located. I consider 25 miles to be a suburb and I have no trouble receiving the HD stations (I've posted demos here). What I read is that people who are 60 miles from an HD station can't receive the HD. Well I've posted a HD station I receive on my Sangean tuner, but that said 60 miles away is not a suburb. 60 miles away is deep fringe. I other words it's outside of the market. I've driven 60 miles from the rransmitters in NYC. Sure the signal can be received but it's spotty at best. Forget power levels, hey with 100 watts or so I am able to hit a geostationary satellite with a solid signal, and that bird is some 20,000 miles away, above the Equator over Hawaii and that's a digital signal. Look at it this way, the diference in RF penetration between today's digital cell phones and the old analog ones is the difference between night and day. I remeber the days of analog mobile phones and on those the batteries lasted maybe 20 minutes and those batteries were relatively enormous. Today you can get more than 24 hours on a cell bettery. Digital is a much more efficiant method of transmission than analog. It's a simple as that.

Digital can work well on VHF over flat terrain. I'm about 36 miles from the KIOI-FM transmitter. That's 125 kW at 1162' HAAT. Yet, I cannot even receive the analog signal in stereo, and everywhere you go there is static from multipath on the 125 kW analog. The Sunol/Pleasanton area on I-680 is only 25 miles from this transmitter, and also has severe multipath problems on the analog, mono only. I don't see how a 100x weaker digital signal is even going to decode. I'm not using crappy receivers either.

They really chose poor frequencies for FM. Unless you tether the transmitters on a balloon 10k' up or have boosters everywhere or use a multi megawatt transmitter, there's no way you can cover this market in analog. I'm sure digital would do wonders for the multipath issue if it were running at full power and not in this inferior hybrid mode. I wonder if you could put multiple antennas on an HD radio receiver and use MIMO to combat multipath and increase usable range. I guess in the present state the HD-1 signals would be no worse than analog as it would just fall back, but the HD-2 would be nearly unusable and subject to constant dropouts when driving most of the major freeways around here for any length of time.

 

[R.F. Burns]

I don't know about you but I live 25 miles from modtown Manhattan where the FM transmitters are located. I consider 25 miles to be a suburb and I have no trouble receiving the HD stations (I've posted demos here). What I read is that people who are 60 miles from an HD station can't receive the HD. Well I've posted a HD station I receive on my Sangean tuner, but that said 60 miles away is not a suburb. 60 miles away is deep fringe. I other words it's outside of the market. I've driven 60 miles from the rransmitters in NYC. Sure the signal can be received but it's spotty at best. Forget power levels, hey with 100 watts or so I am able to hit a geostationary satellite with a solid signal, and that bird is some 20,000 miles away, above the Equator over Hawaii and that's a digital signal. Look at it this way, the diference in RF penetration between today's digital cell phones and the old analog ones is the difference between night and day. I remeber the days of analog mobile phones and on those the batteries lasted maybe 20 minutes and those batteries were relatively enormous. Today you can get more than 24 hours on a cell bettery. Digital is a much more efficiant method of transmission than analog. It's a simple as that.

Digital can work well on VHF over flat terrain. I'm about 36 miles from the KIOI-FM transmitter. That's 125 kW at 1162' HAAT. Yet, I cannot even receive the analog signal in stereo, and everywhere you go there is static from multipath on the 125 kW analog. The Sunol/Pleasanton area on I-680 is only 25 miles from this transmitter, and also has severe multipath problems on the analog, mono only. I don't see how a 100x weaker digital signal is even going to decode. I'm not using crappy receivers either.

They really chose poor frequencies for FM. Unless you tether the transmitters on a balloon 10k' up or have boosters everywhere or use a multi megawatt transmitter, there's no way you can cover this market in analog. I'm sure digital would do wonders for the multipath issue if it were running at full power and not in this inferior hybrid mode. I wonder if you could put multiple antennas on an HD radio receiver and use MIMO to combat multipath and increase usable range. I guess in the present state the HD-1 signals would be no worse than analog as it would just fall back, but the HD-2 would be nearly unusable and subject to constant dropouts when driving most of the major freeways around here for any length of time.

I don't know about your circumstance but in NYC whch is a cavern of skyscrapers and where multipath is a major issue, UHF has proven to have better penetration. That's why in the UK they've used UHF for years and in the US the new TV allocations are nearly 100% UHF. Digital signals are not prone to multipath and again, you can't equate analog standards of power with the needs of digital transmission. I'd be curious to find out where you have such terrible coverage from stations who's towers are 1100 plus feet haat. Unless you are behind an enoromous mountain, I don't see how you'd have trouble receiving a clean signal. Remember, HD digital isn't prone to multipath. in NYC most of our stations are over 1300 foot above ground (They used to be over 1500 before we lost the WTC) but due to the very crowded region we are in our stations are operating at 6 - 7 KW or so and they can easily be heard 50 or so miles away. Even with my Receptor and FM dipole I had no trouble listening to the NY stations 40 miles away. All NY AM's were loud and clear in IBOC using just the atached loop. In my area that's a location that's more then a 1 hour trip from NYC.

 

[awj223]

I don't know about your circumstance but in NYC whch is a cavern of skyscrapers and where multipath is a major issue, UHF has proven to have better penetration. That's why in the UK they've used UHF for years and in the US the new TV allocations are nearly 100% UHF. Digital signals are not prone to multipath and again, you can't equate analog standards of power with the needs of digital transmission. I'd be curious to find out where you have such terrible coverage from stations who's towers are 1100 plus feet haat. Unless you are behind an enoromous mountain, I don't see how you'd have trouble receiving a clean signal. Remember, HD digital isn't prone to multipath. in NYC most of our stations are over 1300 foot above ground (They used to be over 1500 before we lost the WTC) but due to the very crowded region we are in our stations are operating at 6 - 7 KW or so and they can easily be heard 50 or so miles away. Even with my Receptor and FM dipole I had no trouble listening to the NY stations 40 miles away. All NY AM's were loud and clear in IBOC using just the atached loop. In my area that's a location that's more then a 1 hour trip from NYC.

KIOI-FM, KYLD-FM, KQED-FM, KBWF-FM, etc. and any other FMs located on San Bruno mountain all have severe multipath trouble in Saratoga/Monte Sereno/Los Gatos, along some sections of I-280, and along I-680 north of Sunol in many, many places. They also have issues along CA-24 between the Caldecott Tunnel and Walnut Creek, not as bad as the other locations but then again that's only 20 miles from San Bruno. Let me put it this way: all of those stations except KQED-FM have boosters on Mt. Diablo which itself is only about 30 miles from the San Bruno transmitter farm. These mainly cover the Concord/Walnut Creek/Pleasanton area but even so there are many areas on major freeways that still have issues because there's still no line of sight to either of those areas, the booster and main signals are interfering with each other (this might be the case on parts of CA-24), or because there are vast areas not well covered by either facility, like the western areas of the Santa Clara Valley. They may be 1200' above average terrain but there is a LOT of terrain out there that's 2000' or more along ridges. You might think that the best place to put the main transmitter is on Mt Diablo itself. That covers SF well but wouldn't reach the eastern sections of Santa Clara County, and the entire urbanized east bay I-880 corridor including Oakland would be in a shadow.

Here are the San Bruno transmitters. Zoom out to see the surrounding terrain. All of that green and brown area is hilly/mountainous terrain. The ridges are for the most part all over 1000', and some ridges are over 2000'. Ridge peaks like Diablo, Hamilton, and Loma Prieta can be over 3000'. Mt Diablo is off to the ENE about 30 miles. http://maps.google.com/?ie=UTF8&om=1&z=18&ll=37.688528,-122.437268&spn=0.001927,0.003648&t=h
You can see why Los Gatos has such a severe multipath problem, as does I-680 around Sunol. I doubt a 100x weaker IBOC sideband is going to fix this. It would be attenuated too much by the terrain. The ONLY stations that currently achieve good signals into all corners of the urban area are the 50kW mediumwave transmitters: KNBR-AM, KCBS-AM, and KGO-AM, which actually get assisted by terrain rather than hurt by it (the Bay has excellent conductivity and all 3 have their transmitters around the shore of the Bay), as well as a few class B AMs less than 50kW at the lower end of the band. The other ones are a few clear channels from outside the market like KFI and KNX, but only at night.

And TV? It's awful in a lot of areas, even with rooftop antennas there are places where you only get 2-3 channels. I haven't used OTA television since before I was 5 years old. You need cable or satellite to just get the local channels clearly. Everybody in this neighborhood has either cable or satellite.

 

[PhilJSmith67]

The point I am making is that I get unacceptable breakups on a VERY STRONG signal. 890 kHz, 19 miles distant, full-quieting analog signal (on two different receivers, BTW). While a small amount of noise from the lightswitch can be heard on the more distant Chicago 50kW signals, it cannot be heard at all with WLS at my location, and I've flipped that switch on and off a hundred times. The distant lightning static from two mornings ago, which was also not apparent in the analog signal, really chewed up the HD Radio digital bitstream. Oh yeah, the receiver interpreted whatever it "heard" as OFDM carriers carrying 1's and 0's, but they weren't the original 1's and 0's being sent by WLS.

There is an obvious physical reality here that static, even a low amount, causes an effective "flipping of bits" to occur. Perhaps 48kbps requires the symbol duration to be too short on each OFDM carrier. But, dropping the bitrate to extend the symbol duration would make the HD audio sound horrid. Perhaps the reality is that there just isn't much that can be done to reliably digitize the MW frequencies around 1 MHz.

Now, I haven't had much problem at all with AM HD Radio during the prior two winter months. A breakup here, a dropout there, but very much acceptable until this week. I just wonder what it will be like when the storm season really shifts into high gear. And, if a little static can cause this much data corruption, just imagine how well HD Radio will work at night when adjacent-channel DX signals dance underneath and through local IBOC sidebands.

 

[PhilJSmith67]

An answer to how a digital signal of 1/100 power can decode... It is indeed due to what R.F. Burns basically said: Digital transmission modes (in this case OFDM) are more efficient than analog. Some digital modes are dramatically more efficient.

For a really simple analogy, think of it like the amount of power it takes to flash a strobe light a few times a second (the digital transmitter), as opposed to having a bright incandescent bulb constantly lit (the analog transmitter). Both can be seen at a distance, which is our goal. But, the strobe "transmitter" is only on for a very, very brief period, as opposed to the incendescent bulb which draws power continuously. If you average the amount of power consumed by both devices over each 1-second interval, the constant lamp could easily burn 100x the power of the strobe light.

On the receiver side, digital modes can also allow for power-efficiency by having receivers use timers to "expect" when a digital "1" will be sent by the strobe light, or a digital "0" where the strobe remains off. The receiver can remain off for the entire time between each expected pulse. Digital cell phones use exactly this principle -- They briefly flip the receiver on just long enough to see if a few bits are being sent by the cell tower to indicate that someone is getting an SMS message or a phone call. With analog receivers, no such luck... They have to "listen" continuously to the analog carrier.

Now, efficiency shouldn't be confused with reliability. As the duration of each of the 1's and 0's is shortened (to increase the bitrate), each bit becomes more susceptible to interference. Of course that's a really simplistic way to put it, but it is also the crux behind some of the discussions about reliability of HD Radio and 8VSB/ATSC digital TV signals.