2 questions about switch to digital television.

1).Currently you can listen to television channel 6 on a radio @ 87.7 FM. When all television is switched to digital will that put an end to listening to Seinfeld and the Simpsons when I’m in my car?

2). After the digital conversion the current TV frequencies are to be reassigned for other purposes like police/fire, etc… Will a television set that only receives analog be able to pick up the audio to those new broadcasts?

  1. Yes.
  2. No.

Extracting the audio from a digital TV signal is very complex and requires a great deal of sophisticated signal processing.

I think you misunderstood #2.

What I mean is, when the analog signals (that are currently being used by TV channels) are reassigned as analog frequencies for other uses, like fire/police/rescue, etc… It’s my understanding that that is one of the reasons for the switch.

Not really. While they are both FM, the deviation is considerably different, and most modern mobile radio systems are trunked (computer controlled channel selection), and use much narrower and more densely packed channels. Some of the newer mobile radio systems are also digital, and incompatible with analog FM.

Question 1 is something that I suspect will cause a bit of frustration and surprise. In the recent week long power outage here we were happy to have a crank powered radio that had a couple of bands for picking up TV sound. The storm information etc on local TV was probably better than on radio. That won’t be available to us next time. Hopefully someone is making low cost radios for digital TV sound.

It’s unlikely that any new radios for newly available frequencies will be analog - especially ones intended for first responders. The days of scanner listening are numbered.

You are probably out of luck there.

More promising is digital transmission of television programming to cellular telephones - this is a promising use of the new bandwidth, and will likely be a very low cost (or advertiser provided) service.

I wouldn’t be so pessimistic about a digital radio for TV sound. Radio Shack are selling a portable 7 inch TV with digital tuner for $179.99. I don’t think there would be any technical reason why someone couldn’t make something like that without the screen and video circuitry for a lot cheaper. I guess it’s just a question of whether there is enough demand to make it worthwhile to produce.

Question 1

Very few stations will be broadcasting on channel 6. The low VHF stations are subject to a lot of interference.

Channels 7 - 13 are high VHF and are good for digital broadcasting.

Because most stations are remaining on their digital channels after the transition, the FCC has mandated something called a PSIP. What this does is it allows for a virtual channel (It also does A LOT more too).

Here’s an example:

WRTV channel 6 in Indianapolis uses channel 25 to broadcast its digital signal. After the transition it will continue to use channel 25. But you won’t know because PSIP will automatically route the channel. So if you type in channel 25, it’ll route automatically to channel 6. If you type in channel 6, it does the same thing.

This was part of a compromise, because TV stations didn’t want to have to build a whole new transmitter for digital and abandon it. But they also didn’t want to switch branding to a new channel. So PSIP was a compromise. This will allow TV stations to keep their digital transmitter and still identify with their old analog channel number

So MOST, but not TV stations will not be broadcasting on the station they are identifying to. It’s a virtual channel number.

Now some TV station, like WLS-TV Chicago, which broadcasts it’s digital channel on channel 52, will return to their old analog channel and convert the transmitter to digital. Channels 52 - 69 will be taken from TV and given to cell phone, wireless Internet and emergency services (a few others too). So WLS had no choice but to return to their analog channel.


Question 2

Analog is not as efficent as digital. You can compress digital. So yes you would be able to hear service IF they were broadcast in analog. However I doubt anyone would be doing this. For instance you used to be able to take scanners and hear cell phone conversations, when most (but not all) cell phone providers switched over to digital the signals scramble so you get nothing.

Remember analog and digital aren’t DIFFERENT types of broadcasting. They are simply different METHODS for using the same frequencies of the radio spectrum

Is 87.7mhz the actual frequency that a TV recieves audio on, or does the station rebroadcast their audio there? If it’s a rebroadcast, I doubt the changeover will affect it.

EDIT: And a quick check of Wikipedia shows that that IS the actual audio frequency for channel 6. I guess you’re screwed.

The important thing to note here is that just because it uses the same frequency band does not mean it will still be analog, and even if it’s still analog it may not use the same type of signal. Other posts appear to conclude that the answer to this is “no.”