On Mon, 15 Mar 2010 17:17:14 -0400, mm
wrote:

I have an clock radio about 30 years old

Any particular maker and model?

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'm not so sure. Get the call letters for each station when they ID.
My guess(tm) is that it's an FM translator or booster:
http://www.fcc.gov/mb/audio/translator.html
We have a local religious station that can be heard on multiple FM
band frequencies. All of them are translators.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558