I searched the web and came across this letter to the International Radio Club of America. I deleted the person's name and address, but this person seems to have found the answer to the question of WTMC having 3 transmitters.
To: "Mailing list for the International Radio Club of America"
Sent: Monday, September 25, 2006 9:59 PM
Subject: [IRCA] WTMC-1380 Delaware Wackiness
> The Delaware Department of Transportation runs WTMC-1380 in Wilmington
> with a listed 520 watts day and 10 watts at night. It's basically a
> glorified TIS, running traffic and public safety ads all day. It puts a
> good signal into Central Delaware during the day. They also announce a
> transmitter on 1380 in Rehoboth Beach which is a true 10-watt TIS. I've
> not heard the Rehoboth station.
>
> Today, at lunch (I work just south of Dover, in Camden DE), I tuned into
> 1380 and heard two different signals from WTMC that were out of sync.
> There was a VERY strong version with another, much weaker version of
> WTMC's audio underneath. I was hearing two different WTMC audios. I
> immediately thought I had the Rehoboth TIS as the weaker station under the
> much stronger Wilmington transmitter, but I realized that the dominant
> signal was very strong, almost too strong for a 500-watt station at 40
> miles in Wilmington. I doubted I was hearing both the Wilmington and
> Rehoboth stations dueling it out on 1380.
>
> A quick check of the FCC database shows another Delaware DOT TIS on 1380
> in Dover, probably at the DelDOT yard in south Dover, WQSF238 with 10
> watts. Was DelDOT running another signal on 1380 from Dover? They aren't
> announcing it. They announce transmitters in Wilmington and Rehoboth
> Beach, but they do not mention any station in Dover. But I think DelDOT
> is running a third transmitter on 1380 as what I'm hearing is too strong
> to be the Wilmington station, and certainly way too strong to be the
> Rehoboth TIS. On the way home from work, I listened to 1380 through Dover
> and DelDOT was very strong but the signal was much weaker by the time I
> got to north Dover, showing that the dominant station I was listening to
> in the Dover area was low powered.
>
> I think now that DelDOT is running 3 stations on 1380. WTMC, the main
> station in Wilmington, the 10-watt TIS in Rehoboth, WPQK925 and a 10-watt
> TIS in Dover. If so, they are not running in sync, at least the Dover and
> Wilmington stations aren't.
>