Listen for yourself-WHAT HD RADIO SOUNDS LIKE AT MY HOUSE--60 to 80 miles out

[Tom Wells]

In western NC, you have terrain with "soft reflector multipath", and while it is multipath, there are no huge, rectangular flat-faced buildings or much of anything like that to give "hard" multipath reflections. I'm guessing most of your signals are from the east, at elevations lower than yours, and most of the reflected RF bouncing off slopes goes "up and out", not causing problems.
IF someone decided to put an office tower 3 miles west of you, (as if that were possible, I bet it's not) you would likely start having problems. And even then only if your location is somewhat flat. But it's not is it?

 

[Mike Walker]

Nope it's not. You're right...I would be very surprised if an office building went up three miles from here. It's about 8 miles to the nearest town (Wilkesboro).

 

[Chuck]

This is a VERY multipath-rich environment. And around here HD works much better under multipath conditions than analog. Next theory

According to Bob Orban (of processing fame) HD is a big improvement in hilly environments that have been previously plagued with multipath problems. He ought to know. He lives in the San Francisco Bay area. It makes sense. Your digital radio is a really a small computer that buffers and stores the information before you actually hear it. That gives it the ability to "fill in the blanks," in exactly the same way as an Internet stream works.

I'd be curious to know the ERP and antenna heights of the stations you sampled. One of my biggest concerns with IBOC on FM is how small stations will be affected by it. If you are 50-100 KW on a 1500 foot tower it is reasonable to expect decent analog reception for as far away as 75-100 miles, assuming there is no co-channel interference. The HD signal in the case of a 100 KW signal is 1% of the analog signal or 1000 watts at more or less the same antenna height. With an outside antenna, it is reasonable that you'd be able to receive those stations at 60-80 miles away in HD as well as in analog. Since you are not moving, you are not generating any new multipath conditions. All you have to do is contend with reflections caused by your surrounding terrain. I’ll bet you also get good analog reception from the stations you have sampled, using the very same antenna. I have my doubts that HD would be useful under the same conditions in a car, unless you enjoy it reverting to anlalog on a regualr basis. Maybe I'm wrong, but friends in Dallas, which is relatively flat, report that some HD 2 signals drop out on a regular basis in their car.

For reasonably high powered stations, HD reception should be pretty good within the city grade area that it is licensed to serve. It should also be OK even inside buildings with nothing more that the rat tail antenna supplied with the radio.

The problem is what happens to lower powered stations? What if the station in question is 1000 watts? Obviously, it wouldn't be receivable on a regular basis at 75 miles away, but I'll bet that its analog coverage is usable for a 25-35 mile radius. The signal would not be strong at that distance, but assuming they broadcast something the public wants to hear, I'll bet they have listeners at that distance. Now add HD to the mix. They will have a 10 watt digital signal. Will that be useful? I’m not sure, but I doubt that it will. How about a 250 watt translator? That' a 2.5 watt digital signal. Lots of translators are WAY less than 250 watts.

I don't have the answers to these questions. My gut feeling is these small stations - and there are lots of them - will find that they have an HD signal that is only useful for two to five miles, and maybe a lot less. It takes power to penetrate through walls, trees, roof tops, etc. There eventually is a point of diminishing returns.

If I'm right about the need for some kind of minimum power level to make this a useful service, then a lot of station that will find this to be worthless technology. I'd like to see us do something that is good for ALL of broadcasting, not just SOME of broadcasting.

Yeah, I know that you are going to say these little stations are insignificant players that probably should never have been authorized in the first place. Maybe so, but some are important parts of their communities. They exist, and I don’t like intentionally doing things that eliminates existing stations.

 

[Mike Walker]

I don't see why small stations should be any different than large stations, with HD penetrating well to perhaps 80 percent of their analog coverage. Remember, a digital signal can be extremely weak, and the radio still be able to tell the difference between a one and a zero. That's all that's necessary.

That's what I believe. But the signals I sampled are all full power outlets, with ERPs in the 100kw range. Those, of course, were the first to go HD...because they have the budget to do it.

Mike

 

[Chuck]

I don't see why small stations should be any different than large stations, with HD penetrating well to perhaps 80 percent of their analog coverage. Remember, a digital signal can be extremely weak, and the radio still be able to tell the difference between a one and a zero. That's all that's necessary.

Well, sort of. Somewhere there is a threshold where it ceases to work. Power is calculated logarithmically. As you know, a 3 db gain is double the power. Somewhere there is a precipitous drop off where the signal, although present, becomes useless. A good analogy is your cell phone which works OK outside on your front porch, but is as dead as Monty Python's parrot back in your bedroom. That happens in my house, and I can see the cell tower from my front porch.

In the case of HD radio, I'm not sure how power versus usable signal strength translates, but the inventors of the process say that the 64 dbu contour is as far as you should reasonably expect it to work, without resorting to extreme measures. For a lot of stations, that isn't all that far away from their antenna site. For rim-shots, the bulk of their intended audience may be well beyond that contour. As for translators and LPFM’s it looks like 2-3 miles would be about it. That seems hardly worth doing.

That's what I believe. But the signals I sampled are all full power outlets, with ERPs in the 100kw range. Those, of course, were the first to go HD...because they have the budget to do it.
Mike

That's what I guessed. Because they are full power signals, they also have little or no co-channel interference. Smaller stations aren't so lucky. There are other stations on the same frequency that are much closer to them geographically than their full power cousins. That proximity is the major reason they are lower power. The idea is to not interfere with each other.

As I see it, HD could be useful technology for large stations. What they choose to do with it remains to be seen. If they are not careful, it could even hurt them, because the additional channels will further fragment their existing audiences.

For most small stations, the cost really outweighs any benefit, either real or imagined. Regardless of your take on the technology, there is little financial enticement for a small station owner to adopt it for quite some time, if ever. For most of them, the money they are contemplating spending is their own. They would get a far better return on their investment by putting that money into growing their existing facility, in terms of talent and programming.

Just my "never so humble" opinion...