The Experiment: In this experiment were going to explore the use of a 2.5:1 Air Core Balun on the Skywire Loop antenna. I have read a lot of post on the internet regarding the use of a 2.5 to 1 Balun to improve the performance of a Skywire loop antenna. I’ve used a 142 foot coax feed Skywire Loop on 40 meter in the past but was not impressed with the antenna performance. So in this experiment will build a 2.5 to 1 Air Core Balun from the documentation available on the internet (See Reference Links: 1:2.5 Balun for multiband Deltaloop). Then will put up a 40 meter Skywire Loop with the 2.5 to 1 Air Core Balun at the feed point.
1. 14 Gauge Wire
2. PVC Core Form
3. PL259 Male
After winding and testing the 2.5 to 1 Air Core Balun with the MFJ 269 Antenna Analyzer. I was confused with the outcome, placing a 125 ohm resistor across A1/A2 antenna lead, I expected to see on the Analyzer readings (1.0-1 swr) with impedance around 50 ohm, instead the SWR was 6.1-1 and the impedance was 125+ ohms on 40 meter.
So expecting it not to work: I put up a close to 128 foot Skywire Loop up 6 feet, connected one corner to the fence, two corners through the tree branches and fourth corner with the 2.5 to 1 Air Core Balun tied to the antenna mast. See prototype Photo
Connected the MFJ Antenna Analyzer to the 2.5 to 1 Air Core Balun, set the Antenna Analyzer to 40 metes and WOW (1.0-1 swr) on 40m, (1.6-1 swr) on 20m, (3.1-1 swr) on 10m all at 50 ohm impedance. What a surprise the 2.5 to 1 Air Core Balun does works, could probably improve swr on other bands by trimming the loop wire length…
Note: The length for the 40 meter Skywire loop came from the AG6IF Talented Balun Website. Under Recommended loop wire length:
2m band about 7.5 feet, mounted vertically for vert. polarized repeaters
10m 35 feet
20m 64 feet
40m 128 feet
80m 250-260 feet
160m 520-550 feet
3/27/2017 – Finally installed the 2.5:1 Air Core Balun for the Skywire Loop Antenna in a water tight box.
I was stunned, to see how well the 40 meter Skywire Loop performed at 6 feet above the ground with a 2.5 to 1 Air Core Balun at the feed point. Compered to the 40m dipole at 30 feet, the 40 meter Skywire Loop with a 2.5 to 1 Air Core Balun up 6 feet preformed almost as well as the 40 meters dipole at 30 feet.
A couple of day’s later decided to move the loop to a different location and up to 10 feet, the loop became very noisy and receive performance went down, the center frequency at 6 feet was 7.160 at (swr 1.0-1 at 50 ohm’s), at 10 feet the center frequency went to 7.000 (swr 1.5-1 47 ohm’s). The loop did not perform as well up 10 feet, did not feel like adjusting the wire length to improver the swr, because in this experiment I just wanted to see if a 2.5 to 1 Balun would work on a Skywire loop.