FM X-Band 76-87.7 Mhz

When the original FM channels were first allocated, most receiver’s and transmitters were tube affairs. Many transmitters had crystals in “ovens”. These were temperature sensitive. There was a “filament” switch which you had to turn on for at least 15 minutes before “sign on” or you would get crazy readings if the transmitter would even come on. The FCC had you fill out a transmitter log every 30 minutes or an hour.* One of the readings was frequency drift.

Now you have FM 2 way communication radios on 12.5 KHZ channels. It should not be too hard for 60 KHz channel to contain two 15Khz analog audio (stereo) and RDS. The old VHF channels were 15 MHz. In theory there are 250 60 KHz “channels”. If you had a channel adjacent spacing that gives you 125 channels. A semi smart radio should be able to tell the difference between TV and Radio signals using RDS. In the analog days, you could not have adjacent VHF channels in the same market. Most markets should have one of the old channels 2 thru 6 “open”. I contend a “smart” receiver could figure out where radio stations are on the old analog VHF channels 2 thru 6. Most typical digital TV sets can find UFH and VHF stations so just tuning 54 MHZ thru 108 MHZ analog audio should not be impossible.

*It’s been over 40 years and sometimes I forget some of the details.

Your math is all wrong..Two way is NARROW deviation and narrow bandwidth...(2.5-5 kHz deviation and 300-3000Hz audio)...BROADCAST is 75kHz deviation and up to 150 kHz bandwidth (base band audio is 0-15k but there are subcarriers for stereo RDS, etc)...

To maintain decent signal to noise ration, the Modulation Index (MI=deviation / highest freq of modulation) must be kept above a 1, preferably higher.......75/15 is 5 but then when you take into account stereo subcarrier (with L-R) at 38kHz and RDS subcarriers, you approach a 1......reducing deviation on FM Broadcast is not the answer.......sorry, but the analogy you use is apples and oranges

ContinuousWave said:

Your math is all wrong..Two way is NARROW deviation and narrow bandwidth...(2.5-5 kHz deviation and 300-3000Hz audio)...BROADCAST is 75kHz deviation and up to 150 kHz bandwidth (base band audio is 0-15k but there are subcarriers for stereo RDS, etc)...

To maintain decent signal to noise ration, the Modulation Index (MI=deviation / highest freq of modulation) must be kept above a 1, preferably higher.......75/15 is 5 but then when you take into account stereo subcarrier (with L-R) at 38kHz and RDS subcarriers, you approach a 1......reducing deviation on FM Broadcast is not the answer.......sorry, but the analogy you use is apples and oranges

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The narrowest FM signal that would be acceptable is probably the ±25 kHz deviation that was used for analog TV sound. I'm not sure if the audio went to 15 kHz, however.

It did to a point but the stereo L-R subcarrier in TV is not 38kHz nor is there RDS, etc above that....so 25kHz deviation could be used (different encoding method...not compatible with FM radios)

I would love to see something like this

76.1 to 82.7 For licensed stations
83.1 to 86.9 For unlicensed 50w 150ft antenna

FCC is being really lazy this could he full done in 2 to 3 yrs

DJboutit3 said:

FCC is being really lazy this could he full done in 2 to 3 yrs

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The FCC has been very clear that it doesn't support any use of this part of the spectrum for traditional radio.

DJboutit3 said:

I would love to see something like this

76.1 to 82.7 For licensed stations
83.1 to 86.9 For unlicensed 50w 150ft antenna

FCC is being really lazy this could he full done in 2 to 3 yrs

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Unlicensed stations? Given the band congestion and poor success of LPFM, I think that would be the LAST thing the broadcast band would need.

I would contend the biggest problem LPFM faces if many stations are operated by those who have little, if any knowledge of radio. For some groups there is an attitude that drives them to ignore successful operations on the premise the programming does not match their ideals. There's something about radio that makes board members think their personal tastes are exactly what the community wants.

To cite an example, one fellow offers 'news and information not heard on local stations' but because he is in a mainly conservative community the more liberal styled shows go unheard by the very folks he wants to reach and the lack of support shows proof of this. He does not see that and struggles to bring in more than $200 a month in revenue. A radio person would look for what the community has in common and program based on the commonality.

ContinuousWave said:

It did to a point but the stereo L-R subcarrier in TV is not 38kHz nor is there RDS, etc above that....so 25kHz deviation could be used (different encoding method...not compatible with FM radios)

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I guess I was not clear. The transmission would be digital over the FM signal. The “smart” receiver would take regular FM 88-108 MHz plus the new service in digital. Since you would not have to worry about legacy receivers in the new service there are many options. I am sure someone who is more up to date on digital compression schemes can come up with something better but here are some examples:

A modified form of the European DAB (which IMHO is amazing), or a reworked form of AM HD could be used. 20 KHz - 8 KHz (analog voice) = 12 KHz or less. That should fit in a 60 KHz “channel” Using the old dial-up technology you can get up to 56 Kbits / sec on less 3.500 KHz POTS (switched) phone circuit so, just using 10.5 KHz audio 168 Kbits / sec. could be achieved. Pandora’s bitrate is 128 for mobile devices.

DavidEduardo said:

It would take 10 years to get up to just half of all cars with factory installs.

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Assuming the auto industry approves.

DavidEduardo said:

People are not buying radios to receive commercial radio. They are buying smartphones. Trendsetters are using streams and on-demand services to get their music and entertainment, and are increasingly abandoning over the air.

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That's why I don't understand how people like Jeff Smulyan are still trying to shove "the FM chip" and "Next Radio" down everyone's throats. Especially, when they spent millions of dollars to retrofit their stations with HD Radio ten years ago, which isn't compatible with Next Radio or the FM chip.

EricStein said:

That's why I don't understand how people like Jeff Smulyan are still trying to shove "the FM chip" and "Next Radio" down everyone's throats. Especially, when they spent millions of dollars to retrofit their stations with HD Radio ten years ago, which isn't compatible with Next Radio or the FM chip.

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The HD radio example is what would probably happen with FM expansion. After 15 years, you'd have maybe a million or so radios sold. Not a good percentage of the population.

Next Radio is a very different issue. The goal is simply to activate the FM chips that are already installed in devices that people already own. He's not trying to "shove" anything. These chips are already there, and they're active in some other countries.

Even if the FCC expanded the band for FM (which I would be in favor of) there would still be the problem of few radios to receive the signals for like the next 20 years.