An Engineer Explains Why HD Sucks

A typically lively discussion on the Radio-Info.com discussion board featuring engineers gone wild started out with the usual swipes at HD radio:

Chuck: Yeah, but it is pretty hard to find any sign of HD radios in most cars. Sure there are a few, but not enough to make any difference. Most people are not going to rip out a perfectly good factory radio to make the switch to HD. It isn’t easy to do and most cars because the factory radio is deeply integrated with other systems on the car. What’s more, the current factory radios sound and work pretty well. Most people simply don’t care enough to do it. This isn’t the 1970’s when people routinely ripped out the horrible factory radios and replaced them with after market units.

On the other hand, Internet connectivity is available on a few cars right now, and will become much more common as time goes on. It is a good bet that it will be very common in the coming years. That’s because it brings a lot more to the table than just a few additional “free” channels, and people are willing to pay for it.

KB10KL: Actually right now they have no clue that HD even exists, let’s be realistic here.

Savage: A large number of factory-optioned HD-capable radios are only available as part of a VERY pricey entertainment and navigation package. In Mercedes-Benz cars the HD-included bundle runs from $3500 to $8000. In Jaguar it’s over 3K. Even Ford’s HD bundle approaches $1K.

The Ford Sync system, OTOH, is a really cool and capable option. It does a lot of thing very well, and very intuitively, seamlessly melding cell tech, internet access and music from a variety of sources including radio. Given the choice most consumers will opt for Sync in vast preference to an additional expenditure for weakly-performing, interference-addled HD.

Then, in response to an HD apologist who claimed that a power increase would make HD hum, the engineer took over (if your idea of major electronics is the TV remote and it still mystifies you, pass on this):

DaveBayArea: Well, it works fine under certain conditions. You need a specific threshold to get above the noise level, and the blanket “so many db below the carrier” doesn’t cut it. Consider two stations, both with theoretically the same Analog coverage. One is 50,000 watts at 500 feet. The other is 4,000 watts at 1580 feet. These are two real stations, both running HD. Their injection level is -20 dbc.  The station with the lower elevation is running HD at an RMS carrier power of 500 watts. It provides an effective HD signal, locking in most vehicles, out to about 30 miles in flat terrain. The station with the higher elevation, however, has superior FM multipath performance in analog mode and can easily be heard on car radios 50 miles away. The HD signal, at 40 watts, drops below the noise threshold of the average HD receiver just a few miles from the transmitter. It’s physics, and the signal diminishes as 1/r-squared. So even though the higher transmitter is still line-of-sight to the receiver the HD signal is gone.

So bring on a power increase. Yes, that can help. But the average signal variation in a moving vehicle is on the order of 20 db (we’ve all noticed bad reception at a stoplight, and you move forward a foot & the signal is good, right?) So even with a full 10 db increase that only brings the high-transmitter signal up to 400 watts, and the HD coverage approaches that of the lower-elevation transmitter. Now, realistically the increase will be 4 db because nobody in those sparsely-populated areas (where they can go up 10 db) is going to shell out the $$ for the high-powered transmitter just so the prairie dogs can hear HD.

Consider also the development of receivers. The new Lexus sports an FM Diversity radio with an unbelievable noise figure. It’s actually two radios in one, connected to two antennas. It samples the noise around the pilot carrier and switches to whichever antenna is receiving the best signal. No more stoplight fades. I rode in one last weekend to Lake Tahoe and we listened to KVMR (Nevada City, CA — check out the theoretical coverage map) from Stockton, CA to Kirkwood along highway 88. This is WAY out of their predicted contour and in mountainous terrain, yet the signal was clean for pretty much the entire trip. There’s strong stations on 89.7 (in Lodi) and 89.3 (in the hills East of Stockton) but the Lexus radio didn’t care.

Interestingly enough, KVMR can’t be heard clearly much closer to their transmitter in Sacramento, because there’s a station on 89.3 running HD. It’s now seven years since HD first appeared in the San Francisco market, and the number of listeners deprived of signals due to interference still far exceeds the number of listeners capable of hearing HD. It was a noble effort, but let’s face it — digital needs a new radio band.

But, hey. What do engineers know? The laws of physics are subject to the vagaries of advertising — and, apparently, the FCC.

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2 Responses

  1. This about says it all – “It’s now seven years since HD first appeared in the San Francisco market, and the number of listeners deprived of signals due to interference still far exceeds the number of listeners capable of hearing HD. It was a noble effort, but let’s face it — digital needs a new radio band.”

  2. “So even though the higher transmitter is still line-of-sight to the receiver the HD signal is gone.”

    A scam and a fraud perpetuated through iBiquity’s constant lies and manipulations from the very beginning. A flawed system that will never work nearly as well as analog. I hope that Keefe/Wolf rip Struble a new a-hole.

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