Get this one. Silver Sensor.
http://www.amazon.com/Philips-PHDTV1-Silver-Digital-Antenna/dp/B0007XDI54http://www.solidsignal.com/prod_display....CFQ8QagodVGCKPgDesigned by a European (UK) company. Licensed/offered over here by either Zenith or Phillips (not Terk's knockoff).
No amp required. Should do the trick indoor w/i 40 miles and even better if you can hang it in a window as you say.
Directional. Point it at the broadcast peak.
If you do amp it, a Channel Master 7775 or 7777 will do the trick. That is what I have at 60+ miles!
Next up might be a 2-bay.
For a quick check, see if you can tune in a local regular NTSC Analog UHF channel with your current TV and a UHF bowtie antenna. If you can, then it's highly likely that you'll be good to go, maybe even just using that UHF bowtie on the new ATSC set, but the Silver Sensor should do it.
Step ups:
Silver Sensor
http://www.hdtvprimer.com/ANTENNAS/silver.htmlSilver Sensor Amplified
DB-2 2-Bay
http://www.hdtvprimer.com/ANTENNAS/DB2.htmlDB-2 2-Bay Amplified.