Piggie

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Aaron62

How likely could those channels really cause interference to existing FM stations though?

EscapeVelocity

Fascinating. I think an expansion of the FM radio broadcasting would be much better use of the bandwidth.

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Piggie

The old aural carrier on Ch6 was 87.75 MHz, and the top of the channel was and still is 88 MHz. There is no guard band between Ch6 and FM, and actually they overlap.

Ch200 on FM is 87.9 MHz inside the Channel 6 spectrum. Granted there are not a lot of FM stations on channel 200 (why they started counting as 200 for FM channels I don't know).

Even Ch 201 is barely outside the band at 88.1 MHz, with it's sidebands legally touching the edge of the Ch 6 TV.

But if you live near any FM between 88 and 92 MHz range, and there is a Ch 6 TV farther away, yes, it become a problem. You will get herringbone on the screen of an analog (now history). But that would seriously affect reception of DTV.

So even though an FM station is assigned 200 KHz wide channel, that doesn't mean 100% of the energy stays inside that 200 KHz. It's simply not possible to built a filter that performs like that. It only has to be a certain db down from the main carrier at 100 KHz either side of the carrier. But if you live within a mile or so of a 100KW FM, then say the spurious radiation outside the channel is down 60 db, which is enormous, is still 1/10th of a watt or 100 milliwatts. This is the same amount of power as an FM microphone uses. And 60 db down is down in the noise on most analyzers or close to the noise. Yet 100 milliwatts at close range will wipe out DTV. That is just like a cell phone next to the TV causing problems.

So yes, they interfere and have to be considered.

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Piggie

Yeapers, E-Skip the biggest problem there for FM radio doesn't bother FM like it does TV. A person can happily be listening to the local Power99 during an E opening and never know it's going on. I know it's happened to me many times, lisening to stations 30 miles to 60 miles away during an opening, or even the little low power 6KW down the street (13.8 miles). All of them unless the skip just happens to be coming from an area with the same channel won't be noticed. E isn't like tropo either where normally the out of town stations are very strong. E can be very strong but can also be very weak.

Impulse noise inherently is not a huge problem with FM receivers. And the modern FMs with spike limiters in them and better IF filters really reduce impulse noise on the band to just about zero. I don't think AM is going away, like the proposal says AM will all move there. But it give a chance for more stations and new digital formats.

If they were to approve the spectrum, I certainly hope the new radio digital is a lot more than MP3............. At least something like 5.1 MPEG4 sound. I might even give recording artists the incentive to record more in 5.1. A lot of FM is listened to in cars and cars can set up with speakers to be a nearly perfect auditorium for sound.

Satellite radio's ONLY advantage is the number of channels available country wide. Long haul drivers never have to hunt stations. Their audio compression is aweful compared to analog FM. Even IBOC is better.

But with more room and new standards and better receivers this could be overcome to a large degree. The stations could transmit more information, so you could program the possible future radios to find the talk or music you were seeking. Most FM listening is done locally I believe so even that would not be a problem.

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