MythTV related question: HD Comcast channels in Cambridge

[qsteenhuis-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org (Quinten Steenhuis)]

Hi,

It was suggested on the MythTV discussion list that I ask this question here.

I just moved to (North) Cambridge from Somerville. I'm using an HD
Homerun box with MythTV. In the past I could tune all of the local
broadcast channels in decent HD using Comcast. Now I don't seem to be
able to see any of those channels. Only a poor-contrast and slightly
fuzzy SD signal. Hulu looks better than this signal.

1) Is this something Comcast recently changed? The SiliconDust website
still says several HD channels are available in clear QAM.
2) Do I need to subscribe to a different package? I only have the
local channel lineup, not the basic cable package.
3) Am I doing something wrong in my scan? I scanned on Cable, HRC, and
IRC frequencies. Got lots of untuneable channels, and the scan picked
up the names of the local broadcast stations (WHDH etc), but not the
HD versions as it had when in Somerville. I also tried using the clear
QAM tuner in my TV, which also failed to pick up any HD channels.

If this is impossible without a cable box, anybody have suggestions on
a good antenna, and what my results are likely to be if I switch to
over the air broadcasts? I had an antenna laying around that worked
for a couple channels, but with too many glitches to use for
recording--however, I was missing the power supply. If I buy a powered
indoor antenna, am I likely to pick up a good number of local HD
stations? I don't think I can afford to install an antenna on the roof
at this point.

Thanks for any insight!

Quinten