[GroundUrMast]

Satellite systems are different from cable, OTA signals can be inserted with the appropriate diplexer. An inexpensive diplexer will not accomplish the task on a terrestrial CATV network. Mixing OTA and terrestrial CATV network signals on the same coax is technically possible but almost always ill-advised. The most critical concern is that you can quite easily transmit interfering signals on aircraft, fire and police frequencies. The cable network is a closed system and can therefor use frequencies assigned to over the air services including life safety services. My advise is, don't risk interfering with life safety services.

On a practical level, most cable networks use QAM and NTSC modulation, the OTA transmissions use ATSC and NTSC modulation. This is why your television setup menu has a selection for 'air' and 'cable'. In addition, the cable network can use channel assignments which do not align with the over the air assignments. The result is that you will not likely find a setting on your TV that will give you the ability to tune both cable and OTA channels without reconfiguring the tuner setup and possibly re-scanning each time you switch modes.

If you are willing to invest in cable grade signal processing equipment and commercial grade test equipment, it's technically possible to convert ATSC to QAM and then insert the QAM into a cable grade signal stream... Can you afford an investment of thousands of dollars per channel plus thousands of dollars of test equipment? And be responsible for any interference you cause?

An A/B switch at the TV is far more practical for most viewers.

Presuming I copied the correct TVFR link...

Most of what I'm about to say is based on your attic being a satisfactory location for OTA reception...

Click on the "Pending Applications - All Channels" radio button and you will see that several of the post digital transition stations will be using high-VHF channel assignments. A UHF only antenna will not offer reliable reception of those channels. You could choose a two antenna solution using the 8-bay panel antenna plus a high-VHF antenna such as the Antennacraft Y5713. You could go with a single combo antenna such as the Antennacraft HBU-33 (or larger) or a Winegard HD7694P (or larger).

If you choose an 8-bay panel antenna, double check the pricing on Antennas Direct DB-8, Antennacraft U-8000, Channel Master CM-4228 and Winegard HD-8800... I am a bit skeptical of the gimmick hinge in the antenna you linked to.

I'm not convinced you will need a preamp. If you do, I would be worried that the CM7777 would overload. An Antennas Direct CPA-19 or Winegard HDP269 would be a better choice for a single antenna setup. For a two antenna system, the Antennacraft 10G221 has dual inputs (UHF/VHF) with high input capacity.