[vt6364]

Did all the tests (took 2 weekends), but haven't had time to get back to posting them until now. Here are the final updates.

First, Outdoor tests: I tried the DB8, then the DB4, then the modified DB4, then the 751, at different locations and directions outdoor. I made a simple 'stand' of corrugated cardboard to hold the DBs upright; the cardboard only clips to the bottom element and not blocking the front of the antenna. For the 751, I mounted it to an 8Ft wooden rod (an old closet pole that I have in my garage), and carried the pole around, pointing it at different directions. All outdoor tests were done with no amp, and with the same 25Ft RG6 connected to one TV that was also moved around following the antennas. And, Yes I re-zero the tuner every time.

Outdoor results ('north' and 'south' here refers to the 80degT and 180degT as plotted by TVF analysis):

- DB8: When high enough (about > 15Ft above ground) it can get almost all channels.
Pointing south, it gets all the south channels, INCLUDING the low VHF CH4.
Pointing north, it gets all channels both from north AND from south, but no CH4 (and some are weak, cutting in and out).
Pointing to other mountains trying to get reflected signals from the north. Got none!
So, I can get the stronger signals from the south reflected off the higher north mountain, but could not get the weaker signals from north reflected off the lower south and west mountains.

- DB4: Quite less powerful than DB8, only got a few channels pointing north.
Pointing south, it gets all south channels EXCEPT the low-VHF CH4.
Pointing to other mountains around trying to get reflected signals from the north, getting none.
So, DB4 is not enough to catch any reflected signals for my location.

- 751: Results very similar to the DB8 (yes, getting CH4 OK). So this antenna is enough for the ranges in my location. Like many of you pointed out, the DB8 can pull in longer range, but I don't need it, while the more-directional 751 helps rejecting multi-path signals reflecting from the surrounding mountains.

- Modified DB4:
Then I added the VHF elements to the DB4 like dmfdmf suggested, using 12-gauge bare copper wire. (Don't have any thicker wires on hand, and couldn't find any aluminum rods like I planned to). It is easier to attach to the front than to the back of the balun box because the screw is secured by a nut on the front (see pictures attached) inside the box. This box is easy to open, the front cap just slip on/off 2 small notches. So I attached the wires to the front instead, using appropriate nuts going on top of the existing nuts.
Result: Still got all the UHF channels the original DB4 got, but this does not help the DB4 to get CH4! I tried it at different T lengths, first at a total of 8Ft across, then cutting it down by 4-in at a time, going down to 6Ft in last test. None of them can pull in CH4 like the DB8 did. So it must be that the other elements and the reflector were altering the signal, because my simple dipole worked before (and I used the same type of wire, indoor).

Next, I attached the 751 to the J-mount it came with, pointing the J pipe down and forward, attached the J-foot to a piece of plywood, and I have a perfect stand. I placed this on top of the flat roof on the back, and it works just as good as when the 751 was on the pole. So being only 16-18-in above the asphalt shingles does not impair it. This is at about the same total height as it was on the pole when carried around on the ground anyway. Didn't try laying it directly on the shingle roof, but no need to (didn’t know it comes with the J mount).

Finally, I took the 751 into my attic. Lots of trials at different directions and placements, placing it (with the J-mount stand) on the attic floor as well as hanging it (w/o the J) close to the top ridge using plastic strings, ...
Results were all similar to the DB8. I never could get any channel from the north, only some from the south, and never get the low-VHF CH4. Then I tried adding the preamp, with a 3-Ft RG6 connecting the TVPRAMP1R to the 751, and the usual 25Ft RG6 going from the preamp down to the single TV. The preamp only helped improving the few analog channels I already got, but did not help getting any more channels.

I returned the DB8 right the following Monday; still have the 751 and the preamp. I believe I have exhausted all possibilities and I cannot get any north channels without mounting an antenna outdoor higher up in front of the house. The only other thing to try is getting a larger Yagi antenna for the attic. I think I have room for either the Winegard 7694 or the CM-5016, but the reviews I read suggest that they are not a lot stronger than the 751 anyway.
So perhaps I will instead settle with the 751 mounted on top of my back flat roof and get only the south channels. At least I will get NBC on the CH4. Will next take my time to run an RG6 through the wall out to the back roof and permanently attach the 751 there. But I need to take a break for a while; with that much tests in many consecutive weekends, it feels I have done nothing but antenna tests for months now :-)

Thanks again for all your inputs. Your services are really appreciated, and I learned quite a bit from the process.