I think the O.P. was referring to my posts. Yes, the attic antenna was the omni-directional Marine antenna. And no, 30 or 40 channels isn't all that good here (College Park, MD, close to Washington, DC, a major urban area) - TVfool.com lists a lot of channels I don't get, and I was counting sub-channels of the same broadcast station (e.g., 4-1, 4-2, 4-3...), most of which TVfool leaves out. I presume I would get more channels if the antenna was not in the attic and was higher up, or if I used a directional antenna. I think the maximum range of that antenna is less than 45 miles - not nearly as good as a good directional antenna.
I used that antenna because I already had it, so the test cost me nothing. What it showed me was that I can get all the major broadcast networks, even with a less-than-optimal antenna. If you don't live in a major metropolitan area, or are surrounded by tall buildings, perhaps that won't be true for you.
It is easier to deal with an omni-directional antenna. E.g., you don't need a lot of fancy circuitry that rotates the antenna on schedule to use a video recorder.
Marine antennas have two advantages, for which you must pay a lot extra - corrosion resistance, and an internal ground plane. As best as I can figure out neither will increase the initial number of channels received, though I suppose that if you get corrosion, that could reduce the number of channels received.
For attic use, I suspect there will be little corrosion, so corrosion resistance doesn't matter. If you are worried about corrosion, an electrician tells me to make your electrical connection more weather-proof by twisting the wires together if connecting two wires, using ILSCO De-Ox paste (not Ideal Noalox - it's for aluminum wires) on the connector and/or wires, surround the connected ends with shrink wrap tubing (and heat shrink it), tap screw-on connections with a hammer after tightening, re-tighten 24 hours later, and make sure you double-nut all screw-on connectors so they don't come loose. If you are really worried, surround your antenna with a radome.
For your house, you've got a real ground plane, so you don't need an internal ground plane. And someone on this board claimed ground planes aren't useful for most TV channels, though I don't know enough to confirm that.
So most people don't bother getting a marine antenna if they don't have a boat, or live right next to salt water.
Edited by grunes, 02 March 2014 - 10:16 PM.