DTV HDTV receivers in a head end

Has anyone used a DTV HDTV receiver to receive off air digital signals for use in a headend, and if so how did they work.

I'm presently using DirecTV as a source for local broadcast channels 4, 5, 7, and 9 in the Washington D.C. market. The site is about 30 miles away from the transmitters, but in a very weak signal area. I am modulating the A/V outputs on-channel, using Holland mini-mods. I would therefore expect the channels I am generating to be substantially similar to ones modulated from an HDTV tuner's A/V outputs, though probably not identical.

I found that the effect of signal ingress, where it occurred, was absolutely devastating to the pictures: far worse than the effects of ingress that I would expect if I were processing these signals through strip amplifiers. While this building is wired with foil shielded wire, the building engineer had made up lots of TV connection cable using copper braid shielded coax with no foil. It was only on these TVs that I had the ingress problem, and I remedied it completely by replacing the coaxes with ordinary, foil shielded coax.

Actually, I am surprised by the fact that I has a 100% success rate in eliminating this interference with the foil shielded wire, because I figured that eventually, I'd come to one room where either the TV tuner's shielding was less than adequate, or the inch or two of 300 ohm twin lead going into the TV's matching balun would pick up some interference, or maybe one of the wall plates would have a bad crimp behind it that would leak in a little signal, but in all 30 rooms where I simply replaced the coax, the pictures went from unwatchable to ideal.

Another surprise was the intensity of the interference, in light of the fact that the coax line signal levels were strong and the ambient broadcast signals had to be relatively weak. Since no one was paying me to make I science fair project out of this job, I didn't experiment as I might have to find out just why the pictures on TVs with the braid-only coax were as bad as they were. I didn't, for example, try distributing a non-broadcast satellite programming on any of the problem channels.

It is within the realm of possibility that one or more of the residents has amplified rabbit ears, which may be broadcasting amplified, off-air reception and were contributing to the problem. I have previously been plagued by residents who have connected a UHF antenna in parallel with their MATV connection to enable them to pick up additional channels that were not included in their MATV channel lineup, but that doesn't seem to be the problem here, since if the undesired signals were being backfed, improving the shielding probably wouldn't have made a difference.

I'd say that if you can't vouch for the integrity of the shileding in the existing distribution wiring, you would be inviting trouble if you try to distribute modulated, HDTV based programming on-channel, pretty much regardless of the broadcast signal strength at the site. On the other hand, you will be strongly motivated to give on-channel modulation a shot, especially if the broadcast channels you are trying to improve are VHF and patrons in your market expect them to be on-channel. I would probably try to keep the customer in the dark while I was experimenting there, because if they see a perfect on-channel picture somewhere but if you find that there is a lot of inaccessible, leaky wiring elsewhere, you may not want the customer pounding on you to undertake the task of bringing all of their wiring up to good enough condition to allow quality on-channel distribution everywhere.

All I was asking was, has anyone used a DTV HDTV receiver to pick up local off-air digital stations, which would be then remodulated to VHF frequences.