Keith, when you say you get 48 digital channels, I'm pretty sure you're counting subchannels, like 3.2, 10.2 etc. So I think you're getting 18 or 19 separate stations, probably all marked LOS (line-of-sight) in the report. This makes perfect sense with that antenna installed in an attic. If you want to know whether a better antenna could improve your lineup, study up on the stations below those you receive in the Fool Report. Look at the stations at 344° (almost straight north by compass) down through all the yellow (NM = 15.4). Wikipedia is a good resource for that. If there's anything you just gotta have, then a better antenna might be a smart investment. Offhand, it doesn't look like there's much interesting below the green.
Possible reasons for three identical antennas in the attic:
- A previous owner sold those antennas.
- Previous owner had them hooked up to three separate receivers. (A perfectly reasonable solution, if there's enough room.)
- Previous owner thought he could improve reception by ganging them together with a three way reverse splitter.
If you gang carefully, with identical lengths of coax, combining antennas CAN sometimes improve reception. But I think the reason gain is moderate on this antenna is very wide beam width. That means they are going to talk to one another, i.e. multipath. Even if somebody had success combining them 30 years ago, that doesn't mean you'll have much luck now. I don't have any experience with ganging, but theoretically there's so many more stations today, you could get a massive traffic jam up there.
Still, it sounds like you want to do that, and it could be a fun experiment. There are probably people here with real world experience on that kind of thing, and it wouldn't cost much. Or you could get a more directional antenna with higher gain for less than $65, and sell the antiques on Craig's list or eBay.
Grounding to the outlet should be OK, as long as you're sure it's really ground you're connecting to. Technically, I don't think grounding is required for an attic antenna, but it's always a good idea.
Combining the two wires to the one coax with a converter is the way to go. Your converter must have a working transformer (balun) or you wouldn't get so many channels.