I started with 116mm segments for a proof of concept following the instructions at https://www.balarad.net/ After having great results compared to a simple ground plane, I built a second antenna and feeder and started tweaking the length 1mm at a time. Having two identical feeders from the same location made it easy to tell if the results were better or worse almost instantly by comparing plane counts, message rates, and range. If the results got better, I would shorten the other antenna to match and make sure the results were comparable. Eventually the results got worse (111mm) and I knew I was in the ballpark of optimal length for my setup. Using that method got me dialed in very close to the optimal length based on the VF for my cable. (112.4mm) Since then, I have played around with amplifiers and filters and have a setup that has been repeatable to build. Currently running two feeders 20 miles apart with nearly identical configuration. Tree cover, height above ground, feed line length, and geographical differences being the largest difference in config.
Current config at both sites:
8x112mm coco --> short feed line --> Paladin 20db Satellite amp --> Feedline (20’ on one 60’ on other) --> Ground block --> 10’ feed line --> DirectTV power inserter (21V) --> 3’ feedline --> R820T2 Dongle --> RPi2
I also had to tweak the gain setting on the dongle one step at a time to get the “optimal” setting for each site. Too high of a gain setting will provide horrible results. One tick in gain level can have a drastic impact on the results.
Feeder 1 (Would like to get 20’ higher to clear tree line.)
38.6db gain, under tree cover, 15’ above ground
Feeder 2 (need to test with antenna mounted on opposite side of tower)
25.4db gain, on Ham tower, above trees, 50’ in air
The only filtering I am using is the 950mhz high pass filter built into the 20db Paladin Satellite amp