I'm trying to receive a UHF TV signal 86 miles away. Considering the height of the transmitting antenna and the height of the receiving antenna, I should be able to just make line-of-sight between them... but the signal will be weak and probably perturbed in a number of ways.
I can now occasionally receive this signal using 1 DB8 "bedspring" antenna. The popular DB8 TV antenna consists of 4 vertically stacked bowties in parallel with 4 vertically stacked bowties. In the center of the lines that connect these two arrays in parallel is a matching transformer to convert the 150 ohm balanced signal from the parallel arrays to a 75 ohm unbalanced output.
I want to vertically stack two DB8s to try to achieve a theoretical +3db additional gain. It seems I should be able to do this by removing the matching transformer from each DB8 and connecting the two antennas in parallel by simply running two parallel lines (spaced and sized appropriately) from the center feed point of the top DB8 to the center feed point of the bottom DB8... in place of the matching transformers. This puts the 150 ohms of the top DB8 in parallel with 150 ohms of the bottom DB8 to yield 75 ohms at the center of the lines connecting the two antennas. Then, using a 1:1 current balun, I can convert the 75 ohms balanced to 75 ohm unbalanced to match my 75 ohm coax downfeed. This is the lowest possible loss method I can imagine to combine two DB8s.
Sounds easy but I've been around a long time and in my experience, antennas seldom behave exactly the way theory predicts. Has anyone ever tried this? Is there a better way?
(Edit: Following Glenn's excellent advice, I've disassembled the baluns on each array and hope to begin experimenting with the phasing harness this weekend. For those interested, below are pictures of the PC board inside balun enclosure.)