Kent said:
So, one area where I do agree with you is that HD isn't going to be the savior of FM radio. In many larger cities, people already commute 100-150 miles round trip every day. Going back to Dallas (which I'm more familiar with because I grew up there), commutes from northern Collin County are common, especially to Plano and the telecom corridor in Richardson. All of those areas are in the far northern part of the Dallas metro, and most of the towers are in far south Dallas. If you live north of McKinney (central Collin County), you're already outside the 60 dBu signal contour, and you'll have some radios that won't be able to get good signals on the south Dallas sticks. HD isn't going to help anyone reach these people.
I did some measurements on Dallas HD stations from about 4 miles North of Van Alstyne, about 64 miles from the DFW antenna farm. I had perfect HD decode on every DFW HD FM station, and on KMKI 620. KAAM 770 was problematic for me, even in the city of Plano 9.4 miles from the KAAM tower. Contrast that to perfect C-Quam reception on KAAM 290 miles away during the daytime, at a rest stop in the Crosbyton canyon. The only issue was the presence of KKOB underneath KAAM, but it didn't cause platform motion until I tried KAAM from Lubbock, another 40 miles West.
I've also measured reception on Houston HD stations and found that they go about 70 miles in HD in my car. I do know, also, that the Missouri City stations are pretty much gone by North of Huntsville. HD probably drops out about 15 to 20 miles South of there, but should be solid in areas like Conroe and the Woodlands. I haven't done a drive test that direction yet.
I find HD to be pretty robust over the city, but there are other problems such as IF images and small nulls which cause HD to dropout as close as 20 miles to the towers. AM HD drops because of power lines by the road. HD reception of AM is seriously compromised by any interference source. I can get AM HD on College Station 1620 about 60 miles away, but it drops immediately anywhere near a power line.
Any new IC would have to actively cancel power line interference to improve AM - theoretically possible if you can characterize exactly the noise waveform and feed it back precisely out of phase at the precise level required to cancel, but that assumes the signal doesn't saturate and a very high bandwidth system to perform the cancellation. I am highly skeptical. As far as FM, no chip can solve the IF image jamming problem, nor can it solve the micro null problem. I find that the micro nulls where HD drops also has degraded analog reception, often dropping analog stereo as well.
The ONLY possible solution to the FM problem would be to move the digital sidebands into the FM channel - as far as I can tell the software will decode sidebands no matter where they are located so no firmware change should be necessary on the receiver end. It would solve the IF image problem, and also the coverage problem. The HD-2 drop to silence problem is still an issue. What is needed is faster locking algorithms.
The solution for AM is to fall back to C-Quam, call it HD, issue firmware updates to any HD radio that doesn't already decode it. AM HD is too prone to interference to be fixed - no matter what the power level, unless they want to allocate 500 kW or more to HD AM and hope it can out-shout the power lines. But I doubt even that would solve the power line problem.
