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[ChrisW6ATV]

Originally Posted by ChrisW6ATV

Interesting-they are running one of those out-of-band "pseudo-FM-radio" stations like the one in New York City. Since it is low-power, it may stay on the air indefinitely and be a remaining source for OTA analog tuner testing.

Originally Posted by wa2ise

Only if the TV set isn't the "intercarrier" IF strip type. That is, a 6MHz wide passband that feeds a video detector, which also produces a 4.5MHz FM sound carrier. Older sets had a completely separate sound IF.

Why would the type of sound IF matter with that low-power TV station? Isn't the sound going to be on 87.75 MHz with 25 kHz deviation, 10dB below the video carrier on 83.25 MHz in any case?

[wa2ise]

Originally Posted by ChrisW6ATV

Why would the type of sound IF matter with that low-power TV station? Isn't the sound going to be on 87.75 MHz with 25 kHz deviation, 10dB below the video carrier on 83.25 MHz in any case?

If there's no picture carrier 4.5MHz below that FM station, most analog TV sets won't demodulate it, as there won't be a signal at 4.5MHz at the video detector diode. (I assume that the FM station at 87.7 or 87.9 has no "video" signal associated with it. Though someone could put up an MTV LPTV station on channel 6 so as to become a fake FM radio station).

If you set a TV to channel 6, or cable channel 96 (cable channel using the spectrum between 88 and 108), inject a local oscillator into the TV set antenna port, along with an antenna picking up FM radio stations, and tune that oscillator to a frequency 4.5MHz below a desired FM station, you should hear it out of the TV set's speaker. It will probably sound overdeviated though.
If your town happens to have two FM stations approx 4.5MHz apart, you may hear a really yucky mix of both their audio.

[zenithfan1]

Originally Posted by wa2ise

If there's no picture carrier 4.5MHz below that FM station, most analog TV sets won't demodulate it, as there won't be a signal at 4.5MHz at the video detector diode. (I assume that the FM station at 87.7 or 87.9 has no "video" signal associated with it. Though someone could put up an MTV LPTV station on channel 6 so as to become a fake FM radio station).

If you set a TV to channel 6, or cable channel 96 (cable channel using the spectrum between 88 and 108), inject a local oscillator into the TV set antenna port, along with an antenna picking up FM radio stations, and tune that oscillator to a frequency 4.5MHz below a desired FM station, you should hear it out of the TV set's speaker. It will probably sound overdeviated though.
If your town happens to have two FM stations approx 4.5MHz apart, you may hear a really yucky mix of both their audio.

It does have picture, scenes of Chicago. I think it is a rule that if there is sound being broadcast, there must be a picture too.

[ChrisW6ATV]

Originally Posted by wa2ise

If there's no picture carrier 4.5MHz below that FM station, most analog TV sets won't demodulate it, as there won't be a signal at 4.5MHz at the video detector diode. (I assume that the FM station at 87.7 or 87.9 has no "video" signal associated with it. Though someone could put up an MTV LPTV station on channel 6 so as to become a fake FM radio station).

As Zenithfan1 said, it does have video programming, though that seems to be just to meet the 'letter of the law" for a TV station license, but not its "spirit". The obtaining of a low-power TV station license on channel 6 with the specific intent to act as a radio station is what I meant by "pseudo-radio-station". New York City has one of these as well, and I saw comments by someone who was disappointed that a particular FM radio tuner could not tune down to 87.75 "properly", when it is of course not in the radio broadcast band at all.