HD in new cars

@ landtuna (post # 20)

“But the 92.7 signal doesn't seem any more robust than the HD2,” you wrote.

But does it seem any less robust?

K224CJ, the analog translator on 92.7, has an ERP of 10 watts at an HAAT of 446 meters. (That’s the functional equivalent of a low-powered Class A primary station, one with 199 watts ERP at the Class A reference height of 100 meters HAAT, or about 3 dB above the minimum Class A power of 100 watts @ 100 meters).

KDKB (93.3), on the other hand, has an ERP of 100 kw at an HAAT of 508 meters. Assuming KDKB’s digital signal is at -20 dBc, it’s 1 kilowatt—still 20 dB higher than 10 watts! And KDKB’s greater antenna height gives it the equivalent of an additional 1.13 dB, for a total advantage of 21.13 dB.

Of course, if KDKB has boosted its digital signal to -14 dBc, the difference is 27.13 dB!

So if you’re saying that the coverage of the two is comparable despite the digital signal having a power advantage of at least 21.13 dB, that doesn’t say much for “HD” radio, does it?

radioskeptic said:

@ landtuna (post # 20)

So if you’re saying that the coverage of the two is comparable despite the digital signal having a power advantage of at least 21.13 dB, that doesn’t say much for “HD” radio, does it?

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I cannot provide extensive coverage examples of 92.7 vs 93.3 HD2 because I haven't driven to the very outskirts of the metro area in all directions. I did provide two examples where there isn't much difference between the two (PHX metro SE towards Tucson via I-10 and PHX metro W towards L.A. via I-10). In both cases the FM signal lasted a bit longer than the HD signal but not by much.

Note also I am not a proponent or defender of HD radio. Just providing some real world examples to people for comparison. Personally, I don't see any listener advantage to HD as I have never been able to tell any significant difference between regular FM and HD.

It takes a darn good audio system to be able to tell the difference. Unlike digital TV where the difference was night and day, FM stereo analog is a darn good system done right, and there is very little difference in quality. If a station adds both HD-2 and HD-3 - depending on the sampling rates to all three - analog is superior. It is a darn shame, too, because straight HD with no sub channels really is better. A single HD-2 and the quality is pretty much equal to analog. But I wouldn't expect people with normal equipment to be able to hear the difference on a station, even if it has no sub-channels.

DavidEduardo said:

Many of the traffic-display GPS systems in new cars use HD data streams to show road conditions. For those systems to function, HD has to be installed.

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Which explains why the traffic information on my GPs is unreliable and give little advance warning of problems.

rbrucecarter5 said:

It takes a darn good audio system to be able to tell the difference. Unlike digital TV where the difference was night and day, FM stereo analog is a darn good system done right, and there is very little difference in quality. If a station adds both HD-2 and HD-3 - depending on the sampling rates to all three - analog is superior. It is a darn shame, too, because straight HD with no sub channels really is better. A single HD-2 and the quality is pretty much equal to analog. But I wouldn't expect people with normal equipment to be able to hear the difference on a station, even if it has no sub-channels.

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Really? I have no difficulty telling the difference between an analog FM and a digitally encoded audio of any form or bitrate.

Casey said:

Really? I have no difficulty telling the difference between an analog FM and a digitally encoded audio of any form or bitrate.

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Same here. FM sounds dull compared to high bitrate audio, while low bitrate audio has annoying warble and artefacts that mar the sound. Worst of all is that most FM music stations use compressed audio files so you get the worst of both worlds, triple bad when it's passed though an HD encoder.

DavidEduardo said:

Do you know for a fact that your car's system uses HD data delivery? Until you confirm that, you can't blame HD.

It could be "late" for many reasons, ranging from the quality of the source data to the processing time by the supplier. Updates via a real-time HD stream should be instantaneous.

I have confirmed my car's data comes via HD and have watched it change instantly in several cases where I was at a gas station next to a freeway where traffic went from good to bad or the reverse; the system did not even have a 60" lag in changing the color coding of the highway.

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Yes. The HD reception dropouts, combined with lack of an adequate antenna make HD an unreliable source for traffic in my my car.

DavidEduardo said:

The problem in a very flat area with full C FM facilities providing the HD facilities is not likely to be the transmission system but the information aggregator / assembler.

The HD delivered data supposedly sends a data stream repeatedly, over and over, so if one small packet is not captured, the next one will be. If you are within the 65 dbu contour of the analog FM signal of the sending station, you should never miss having updated information.

However, in many parts of the country, electronic monitoring is not as good or responsive, so the highway data is incomplete, delayed or inaccurate. You get it on time, but it is not accurate and up to date.

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The flaw in the logic of these 65 dBu contours is twofold:

(1) Not factoring in receiver antenna, or receiver design. If the antenna is not efficient at FM frequencies, 65 dBu will not be presented to the front end of the receiver. And if the receiver has a poor RF design - like one of those radio on a chip designs implemented poorly (one sided PC board with no decoupling) - a 65 dBu signal will not be enough. Unfortunately those two shortcomings are often found together. My post mortem of a $100 consumer radio shows the problem: http://earmark.net/gesr/Current_Radio_Design.htm I concentrate heavily on the AM aspects in the analysis, but the FM antenna was a short 8 inch piece of wire sticking out the back of the radio. The board is single-sided (no ground plane - which is critical for FM). Car radios are usually not much better, they may add an RF amplifier and a second FM ceramic filter. But with a microcontroller screaming out its clock frequency on a single-sided PC board, with no ground plane let alone no separation of analog and digital, sensitivity is poor. Garbage design predominates.

(2) Another thing that bothers me about 65 dBu contours is they are often drawn as circles. This ignores the true nature of RF propagation which has micro nodes and nulls all over the place, and decades of signal strength swing in feet. Even with the full class C towers easily in sight near my home and commute, there are still dropouts at the same places regardless of vehicle or the radio installed in it, including DX models like the Pioneer Supertuner 3D with a true whip antenna on it. The dropout may be smaller in area, but it is just as deep. Midway between lights A and B on street C - there is a weak signal area on station D, no matter what the receiver. HD drops out - dependably. So in those dropout areas, you can take that neat 65 dBu circle map, crumple it up and throw it away, because it doesn't have the resolution to show true coverage. If you find dozens of dropouts along city streets, there are probably hundreds or thousands all over subdivisions. Who knows how many listeners are lost due to this?

65 dBu circles? Grossly representative of station coverage on a good radio with no other factors limiting reception. Relying on HD for disseminating critical information - not the best distribution method.

Just my experience. LARGE dropout on I-10 between highway 6 and Barker Cypress on whatever FM station is being used to distribute the information. That is several miles of unreliable traffic - which has caught me and thousands of other commuters behind a wreck more than once!

DavidEduardo said:

The fact that there is occasional dropout or multipath is why the data bursts are repeated over and over and over. In the course of a minute or two you get multiple iterations of the same data.

Again, they likely issue is the traffic data provider and the availability of real time sensor data from every road and highway. If the government agencies do not have adequate coverage via monitoring devices or the data is not rapidly processed, then the data provider is using "old" information whether they use HD or a gigantic megaphone.

This is no different than the system used to send the PPM ratings encoding... they repeat it as often as 12 times a minute to make sure that at least some of the code tags make it to the PPM device.

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Too bad they can't use redundancy to stop the problem of HD-2 audio dropout.

rbrucecarter5 said:

Too bad they can't use redundancy to stop the problem of HD-2 audio dropout.

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We've tried to explain this to you several times Bruce:

1. The HD2 data stream is the same stream as the HD1, just that the bit rate is split between the two. If you are able to receive the HD1, you will be for the HD2 as well.

2. Just because you in particular have trouble with reception of your local HD2 favorite is not indicative of all HD channels, one two or three, inside or outside of Houston. Stop generalizing like you know it happens everywhere else. You are wrong.

Kelly A said:

We've tried to explain this to you several times Bruce:

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1. The HD2 data stream is the same stream as the HD1, just that the bit rate is split between the two. If you are able to receive the HD1, you will be for the HD2 as well.

I know that, Kelly. I am sure HD-1 drops out as well. I am simply not interested in the HD-1 of the station. It is a different format.

2. Just because you in particular have trouble with reception of your local HD2 favorite is not indicative of all HD channels, one two or three, inside or outside of Houston. Stop generalizing like you know it happens everywhere else. You are wrong.

Because most of the HD stations with HD-2's come from a single antenna farm, they are pretty much a point source even 20 miles away. If one drops in a particular area, it is a safe bet the others do, too. Maybe to a lesser or greater extent due to geometries that are very small fractions of degrees at the receiving site 20 miles away.

Actually, some of the worst dropouts are going under overpasses on I-10 and 290. These new widened freeways have underpasses that are more like tunnels than they are underpasses, and HD drops because the whole FM band is seriously degraded. Get stuck making a turn under on of those 15 lane monsters, you can be without HD-2 for a minute or more. Regardless of which station it is.

Kelly A said:

We've tried to explain this to you several times Bruce:

1. The HD2 data stream is the same stream as the HD1, just that the bit rate is split between the two. If you are able to receive the HD1, you will be for the HD2 as well.

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But not necessarily the HD3/4, though, right? I understand those use some sort of extended mode. My experience has been that the HD3 of the few local stations that use them are much more difficult to receive than the HD1/2 channels, often not picking up unless I'm within 15-20 miles of the tower site, while the HD1/2 work off-and-on out to a good 45-50 miles.

Someone on the other side of the state has complained that the HD1 and HD3 channels of a nearby station work fine but the HD2 does not come in at all on the fringe, which makes me wonder if the extended data can be assigned to the 2nd channel instead of 3rd for some reason.

DavidEduardo said:

There is only one HD "signal" which can be used just for the simulcast of analog, or split in a variety of bandwidth options for multiple streams.

The bandwidth of the HD signal is finite. If there are two HD streams, it can be divided equally, or with more for one than the other. The one with lower bandwidth has lower quality. This extends to the HD-3 and HD-4 and beyond. Same signal, just divided into greater and lesser bandwith "pieces of the pie".

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So, what's the deal with the so-called "extended hybrid mode" I've heard about before… just fiction?

DavidEduardo said:

Unless a master antenna is being used for all stations, there are many other variables.

1. Different towers.
2. Different antenna height
3. Different antenna facing.
4. Different manufacturer.
5. Imperfect bandwidth of a master antenna across all 20 MHz of the band.
6. Imperfect bandwidth symmetry of a single station antenna.
7. Slight mechanical distortion of the antenna due to mounting, lightening strikes, years of wind stress, bumps by riggers, etc.

And the biggie,

1. Differences of the reception system at different places on the FM band.

Kelly, did I leave any out?

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You covered most of the antenna variables David. Depending on the installed overall transmission system and how well maintained, one can also factor in things like AM noise levels (synchronous or asynchronous) and total group delay through the system. The fact is that some stations pay more attention to their installation design and maintenance, while others just do the minimum.

As David did say rightfully though; 50% of reception quality is at the point of reception.