On 10/28/2014 11:11 PM, micky wrote:
On Tue, 28 Oct 2014 16:39:16 -0400, Michael Black wrote:

On Tue, 28 Oct 2014, Paul Drahn wrote:

On 10/27/2014 9:32 AM, micky wrote:
How can the same FM station appear at two different spots on the dial?

To the person who complained recently that I was off topic, I'm sorry.
This is not about any repair it would be feasible to make. It's only
about electronics.

Where I live there are two FM radio stations, 88.1 which is only a few
miles away, and 88.5 which is 40 or 50 miles away.

Right now, only my expensive KLM radio plus any car radio gets the
second one well, but I've had some cheap radios that do almost as well.

I lose track of which radios those are, so I'll start tuning at 88.1 and
tune up very gradually. After a period of silence, when I get above
88.5 to what I'd estimate is 88.6 or .7 or .8 I get 88.1 again.

How is that happening? I know about harmonics, but that doesn't apply,
does it?



P.S. This means 88.5 doesn't come in at all. I've tried stretching
out the power cord, which on the cheap radios is usually the antenna.
Sometimes that helps but on most of the radios, 88.5 won't come in at
all.

P.P.S. 88.1 is WYPR Baltimore. 88.5 is WAMU in DC. Sometimes they
play the same thing, like during the top of the hour news, Diane Rehm,
etc. although WAMU is on a 5 or 10 second delay most of the time.
Because the topic and the voices can be the same it means I can't tell
for a while if I've gotten 88.5 or just another 'instance' of 88.1.

If you have the AFC on, the station will pop up at different dial locations
depending on which direction you are tuning. At least my old portable does.

I think I've noticed this too.

But the AFC wasn't on, because that would have made it almost impossible
to get a weak station like 88.5.

Well, I'm calling it weak because most radios won't get it, but Wikip
says that it's 50,000 watts ERF (sp?) but 88.1 is only 15,500 watts.
(also ERF? It didnt' say.) So maybe I'm calling it weak because it
farther away, in DC, not Baltimore where I live, but actually, there are
places north of here, farther from DC, the Westminster, Md. area, where
88.5 comes in well and 88.1 barely comes in. A friend moved to
Finksberg and she had to change to 88.5.

But maybe the FCC makes them arrange their antennas so that in the city
of Baltimore and its populous suburbs, 88.5 doesn't overpower 88.1.
But the frequencies are different, and there's no Baltimore 88.5, so why
would 88.5's antennas have to avoid the populous part of Baltimore, or
any part?

I was thinking along that line, except thinking of pointing out that for
whatever reasons, not great selectivity or a noisy synthesizer, a station
can be heard on more than one frequency. But, I can't recall that
happening when there's an adjacent station, then the first station being
received further up.

If that second station wasn't there, AFC is a good suggestion, and
something we might not think of much anymore, with so many fm receivers
digitally tuned. But I'd think it would "lock" to the statino further up,
that presumably is stronger at that point than the first station.

Michael

The fcc.info link I sent lets you search the FCC database in a friendly
gui fashion