Antenna Fun…

Well, I bought a 40′ fiberglass pole from Spiderbeam and wanted to make a 1/4 wave 40 meter antenna that is portable. I have to thank Dave K1KK for planting the idea and putting a hole in my wallet. So I hammered a 4′ long 1/2″ steel tube I got from Lowes into the ground and put velcro on it. I then could place the 40′ mast against it and it would hold the pole up. I taped Green 14 ga wire to the side about 33.2′ long to the mast (Yes it must be green wire, David!). At one end I used velcro to attach a 1:1 Balun to the pole and connected the vertical element to it. Ground wires were about 30.5′ long and were tied to two more steel poles raising the ground wires to about 3′ above the true ground. I attached a coaxial cable to the balun and ran it into the shack where I analyzed the SWR. After shortening and lengthening the radials and the driven element, I came to the best SWR reading for a resonant antenna.

When the ground wires were laying on the ground, the antenna had a lower frequency resonance point as if the antenna was too long. Elevating the radials brought it into the middle of the band. You can see where the phase (purple line) crosses zero axis line is the lowest SWR (red line). Pretty good for messing around with wire antennas. Comparing this vertical to a Carolina windom 10-180 m off center fed antenna, it had signals that were S7 while the Windom was S5. A vertical will have a little more noise on it compared to a dipole but performed well and is a portable antenna.

Red line = SWR, Where the Purple line crosses zero is the lowest SWR (phase).

Next I tried another vertical on 20 meters designed for QRP work and portable operating. This one is made by Silvertip Antennas and consists of a 17′ fiberglass pole tied to a post in the ground. It uses the thin wire from an ethernet cable as the radio ground. At first it seemed to be too short. I tried to coil up the ground wires but that did not help. I took off the coiled choke I made from PVC pipe and replaced it with three small ferrites on the feeding coaxial cable. That did improve the signal but the best improvement was moving the antenna up the support pole. There was a right fit where the end of the driven element hanging down (red wire) was just 2″ from the ground. This had the effect of centering the middle of the SWR curve in the middle of the band.

Array Solutions Vector Network Analyser.

The AIM 4170D and the software scanned the antennas and swept the frequencies showing the relationships of SWR with the phase and reactance. You can do small changes in your antennas and compare how you are doing taking the guess work out of building antennas. A really good investment (Thanks Dave for making me get this thing and showing me how to use it, a real elmer!).

Enjoy the bands, 73 Peter.

Published by DrPVH

Concerned citizen with a multitude of interests...

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