not receiving digital over-the-air

We have an HDTV with an integrated digital tuner.  Our local TV
station advertises free digital over-the-air reception (www.wbng.com)
on digital channel 7.  But all we are getting is its analog version
channel 12.  The antenna is a popular Radio Shack brand with an
amplifier, a "rabbit ears" antenna which has a coaxil connection to
the back of the TV.  The antenna claimed it would work with HDTV sets
on the box.  Is there a difference between digital and analog
antennas?  Could the signal not be strong enough?

The analog channel 12 comes in fairly well but not great.  We have
DirectTV for our main channels which doesn't come with local channels.
Thanks.  --Tim