Today’s activation of Cairngaver was mainly to try out my new end-fed antenna and matching unit. Experts disagree on whether or not you need a counterpoise when end-feeding an antenna which is a half wavelength long, or multiples of half a wavelength. However, Steve Yates AA5TB has put a lot of thought and common sense into this. On his excellent website http://www.aa5tb.com Steve describes a matching unit for 40M to 17M.
I more or less copied Steve’s design, and added a Dan Tayloe N7VE resistive SWR bridge, assembling it in a small plastic box. The resulting matching unit weighs just 80 grams, and will match an end-fed half wave antenna on 40M, 30M and 20M.
Today I used a 20M long piece of PVC covered 24/0.2 wire, weighing about 200 grams. I had previously trimmed it to resonance according to AA5TB’s instructions. Being a resonant half-wave on 40M, it will also work on 20M as a full wavelength, requiring a similar high-impedance feed.
Based on an experiment at the same summit last week, I set up the antenna as an inverted vee slung over a tree, with the apex up 6m, and arms at about 120 degrees. As suggested by AA5TB’s theory, I used no counterpoise at all. When set up in this way, everything was completely stable, with no susceptibility to hand capacitance effects. Apparently the FT-817, key and headphones provide a sufficiently high impedance return path for the antenna to kick against.
Results? On 40M with my 2.5W output I got 599 reports from France and England, 589 from Switzerland, and 569 from Norway. Changing to 20M, requiring just a tweak of the tuning knob on the matching unit, I got 599 reports from Bosnia Herzegovina, Czech Republic and Switzerland. Looks like Steve Yates AA5TB is right!
I will post a picture of the matching unit.