Digital radio technology: why is reception so inconsistent?

Factual Questions
1

I couldn’t really come up with a good title for this thread. Sorry,.

Anyhow, my iPhone has a transmitting power of only milliwatts; it makes 1970s-era walkie-talkies seem incredibly powerful by comparison. Still, it can make a call through a cell tower miles away.

Sirius satellites transmit at about 2,000 watts, or twice the wattage of a low-power AM radio station in the US, at an altitude of 22,000 miles (cite). I can receive Sirius signals perfectly in my car, with no artifacts, dropouts, or other interruptions in the open or under a tree canopy.

Over-the-air ATSC HDTV stations in the US transmit at a power of hundreds of thousands of watts. Even when I’m relatively close to a transmitter and have a good antenna, though, OTA HDTV signals are full of artifacts, drop out constantly, and are … well, incredibly finicky despite the high transmitter strength.

HD radio: same thing. With high-powered FM stations, when I’m more than five to ten miles from a transmitter, I can barely a lock on the HD signal, even with a decent amplified antenna.

So, my question: how come it seems so easy to receive weak digital radio signals (e.g. low-power cell phones transmitting to cell towers miles away, satellite radio transmitting from tens of thousands of miles away), but it’s a struggle to receive high-power signals like ATSC HDTV, and HD radio?

2

First of all broadcasting signals are not the same.

ATSC was the best system (supposedly) for the USA because it’s a huge country. CODFM a competing system is much better at handling things like TV. So why did the USA choose the ATSC standard? ATSC is 8-VSB in actuality.

The reason is ATSC is better over long distances.

Radio and TV are set up to have ONE and ONE tower only. And that tower will serve a broadcast market. For instance, ABC owns a station in Chicago, but it’s Milwaukee, South Bend and Rockford stations are NOT owned by ABC. They are owned by others and just play ABC network shows.

In other countries which use CODFM, this isn’t really needed. The stations are pretty much relays of the central station. There’s no localism. Thus the need to have towers that transmit over large areas are not needed.

Cell phone towers are everywhere. They don’t cover a large area. Sirus Radio is similar in that it is meant to cover everything.

ATSC is better at covering large areas. So yes, people like me in Chicago with tall building were shortchanged, but had CODFM been used, you’d have had to use multiple towers and channels.

The idea is to LIMIT the bandwidth. So in otherwords in theory you can use one ATSC channel to cover where two CODFM channels would cover similar area.

OK this is oversimplifying it, but that is how the theory went. Of course ATSC was adopted in the mid 90s. It’s hopelessly outdate. And that’s not a knock, as any techonolgy would be.

ATSC had to function WITH analog. It’s not like they turned off anaolg and turned on digital. Cell phones and Sirus didn’t have to develop to replecate any analog service. They appeared as new forms of broadcasting.

When you think of it this way, you can see why developers of Sirus and cellphone were free to use any type of technology they wanted. Developers of ATSC and HD radio had to make sure that the frequencies they used would not interfer with the existing ones.

You will not how many times cell phones moved from analog to digital and then to various frequencies.

Again, I’m oversimplify a lot but that the gist of it. Cell phones are designed to serve a small area and Sirus is designed to serve everyone.

ATSC and HD radio were designed to serve a TV/radio market and that market alone.

3

I can’t answer for HD radio, but when it comes to television, even a small bit stream error in a compressed digital video stream can be a disaster for several frames in a row, and the amount of data transferred is significant – that means that you need a good signal to be able to transmit it without choppiness or green block noise covering half the screen.

4

I can answer for HD radio - the digital broadcast power is 1% of the radio station’s total power, but the total output (analog+digital) remains the same. For example, if a 10000 watt station started broadcasting in HD, the HD signal would be 100 watts and the analog signal would drop down to 9900 watts. So it’s probably not as powerful as you may think.

There was a proposal a year or two ago to double the allowed HD power to 2% of total. but I don’t know what happened to it.