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From: mm on 15 Mar 2010 17:17
I have an clock radio about 30 years old that, when tuning for 88.5
FM, for example, by turning the dial, will find that station, and then
a little higher will be another station, and a little higher still
will be 88.5 again, often a stronger signal than the first one.

I'm sure it's not a second station playing the same stuff.

I know about harmonics on AM MW and Short Wave, but here the tuned
frequencies are so close, and also I didn't think there was stuff like
this involving FM. What is going on?
From: Sjouke Burry on 15 Mar 2010 17:37
mm wrote:
> I have an clock radio about 30 years old that, when tuning for 88.5
> FM, for example, by turning the dial, will find that station, and then
> a little higher will be another station, and a little higher still
> will be 88.5 again, often a stronger signal than the first one.
>
> I'm sure it's not a second station playing the same stuff.
>
> I know about harmonics on AM MW and Short Wave, but here the tuned
> frequencies are so close, and also I didn't think there was stuff like
> this involving FM. What is going on?
Intermodulation maybe? Or even something oscillating in the radio inter-
modulating the station?
Or a support transmitter in mountainous country put on some hilltop?
Or a far away second transmitter?
In my country I can find the same station on several frequencies,
because one transmitter cant cover the entire country.
From: William R. Walsh on 15 Mar 2010 17:45
Hi!

> I have an clock radio about 30 years old that, when tuning for 88.5
> FM, for example, by turning the dial, will find that station, and then
> a little higher will be another station, and a little higher still
> will be 88.5 again, often a stronger signal than the first one.

If you're in the US, the low end of the FM band is used by public
radio operators. These stations may be low power or intended to serve
a large area (as is sometimes the case with public radio stations).
The station may in fact operate on multiple frequencies. They may
advertise this fact during station ID.

But sometimes strange things do happen. The other day I was listening
to the Delco AM/FM/Cassette radio in a 1988 Buick. This is a digitally
tuned radio or "ETR" in GM parlance. I bumped the tuning knob,
advancing the frequency from 99.1 to 99.7. Imagine my surprise when
the same station--with the same call sign and frequency announcement--
was found to be playing in perfect fidelity!

The surest thing to try is another radio, situated in another area
(another room ought to do).

And if you have one of those older Delco radios, here's something for
you to try one day if you're bored:

http://greyghost.mooo.com/delco/

William
From: mm on 15 Mar 2010 17:54
On Mon, 15 Mar 2010 14:45:05 -0700 (PDT), "William R. Walsh"
<wm_walsh(a)hotmail.com> wrote:

>Hi!
>
>> I have an clock radio about 30 years old that, when tuning for 88.5
>> FM, for example, by turning the dial, will find that station, and then
>> a little higher will be another station, and a little higher still
>> will be 88.5 again, often a stronger signal than the first one.
>
>If you're in the US, the low end of the FM band is used by public
>radio operators. These stations may be low power or intended to serve
>a large area (as is sometimes the case with public radio stations).

That's right. This is 88.5, WAMU, American University in Washington,
DC, an NPR station. I'm in Baltimore 35 miles north of DC (though I'm
not sure where the antenna is) and it comes in well almost everywhere
in Baltimore and 20 or 30 miles or more north of here.

>The station may in fact operate on multiple frequencies. They may
>advertise this fact during station ID.

I've been listening for 10 years. Never any reference to that. In fact
88.1 is a Balt. NPR station, and 88.3 is something else. Also not
much in the way of hills around here, until 50 or 60 miles west

>But sometimes strange things do happen. The other day I was listening
>to the Delco AM/FM/Cassette radio in a 1988 Buick. This is a digitally
>tuned radio or "ETR" in GM parlance. I bumped the tuning knob,
>advancing the frequency from 99.1 to 99.7. Imagine my surprise when
>the same station--with the same call sign and frequency announcement--
>was found to be playing in perfect fidelity!
>
>The surest thing to try is another radio, situated in another area
>(another room ought to do).
>
>And if you have one of those older Delco radios, here's something for
>you to try one day if you're bored:
>
>http://greyghost.mooo.com/delco/
>
>William

From: mm on 15 Mar 2010 18:01
On Mon, 15 Mar 2010 14:45:05 -0700 (PDT), "William R. Walsh"
<wm_walsh(a)hotmail.com> wrote:

>
>And if you have one of those older Delco radios, here's something for
>you to try one day if you're bored:
>
>http://greyghost.mooo.com/delco/
>
>William

I had 3 GM cars in a row, and I'd like to get back to GM. I heard
about some GM convertible last week and googled for it, only to find
out it's a Pontiac, which afaik, they don't make any more. (And the
Pontiac convertibles I've seen were pretty stripped down). But with
the re-org, maybe Cadillac will make one other than the 2-seater.
I'll be looking for a car about 5 to 7 years old, and I'm glad to know
about this because 4 presets really isn't enough.

(Chrysler has 10 AM and 10 FM. Last I checked for the 80 to 95 cars,
Chrysler had 3 companies making them at one time or another, or maybe
even simultaneiously, even though they all looked alike.)
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