TELECOM Digest OnLine - Sorted: Re: What Happened To Channel 1

Re: What Happened To Channel 1

Paul Coxwell (paulcoxwell@tiscali.co.uk)
Mon, 21 Mar 2005 12:46:11 -0000

> If you look at a digital "world band" radio, you will find somewhere a
> "europe-america" switch. It's often well hidden. I have one where it's
> in the battery compartment. In the Americas the channels on the AM
> band are spaced 10 kHz apart. In Europe they are spaced 9 kHz apart,
> allowing them to squeeze in a few extra stations. This is significant
> only in digital tuning, especially in digital search.

The allocations here were also all shifted upward by 1kHz following a
WARC conference in 1978, so 899, 908, 917kHz became 900, 909, 918 etc.

> There is something similar in FM. I've forgotten the exact details,
> but in US we use only the "odd" frequencies: 88.1, 88.3, 88.5, 88.7,
> 88.9 MHz. I think in some parts of the world they use the even
> frequencies: 88.2, 88.4 etc. This is to get the necessary spacing
> between the broadcasts.

Yes, FM broadcasts in Europe use both even and odd slots, and in
Britain there have even been some stations given a 50kHz allocation,
i.e. xx.x5 MHz.

> One other peculiarity: in most countries, FM is about 88 to 108
> MHz. In Japan it's about 78 to 98 MHz. There are a few radios that
> will receive the entire band, 78 to 108, but most, including Japanese
> brands sold outside Japan, miss the low end of the Japanese band.

The former Soviet Bloc countries in eastern Europe also had their own
FM band. I can't remember the details, but I think it was somewhere
around the 60 to 70MHz region.

In Britain, the original FM broadcast band ran only from 88 to 100MHz.
The band above 100MHz was used for two-way radio, a fact soon
discovered by even the casual listener when imported radios covering
right up to 108MHz started to appear in the country. The broadcast
band was extended right up to 108MHz after the other services had been
moved to different frequencies in the 1980s.

Another minor technical variation here is that we use a different
pre-emphasis curve on FM broadcasts: 50uS vs. 75uS.

- Paul.

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