Not much to report from me lately. The weather was not suitable for portable operations, otherwise too busy or too tired to do anything “radio”. We decided to spend our last money on a trip to Europe this summer (necessary family visits, long overdue) and I am one to prepare way in advance.
“What radio shall I bring along?” was of course the first question I asked myself. But being wise I quickly changed it into: “What antenna shall I use?” Since I never worked with end-fed antennas I thought it would be a good opportunity to learn about them and try them out.
Let’s start with buying stuff: a seven meter fishing rod that fit in my suitcase cost US$20. A length of 30 meter strong light Teflon coated copper wire was about the same. Cut in two lengths of 20 and 10 meter it would cover 20 and 40 meters, hence End Fed Half Wave. For the impedance coupler I turned to M0UKD’s excellent website . End fed antennas are no rocket science: the high impedance of a half wave length of wire has to be turned into a low impedance that matches the radio. A tank circuit is used to optimize the power transfer of the transformer used for this. So I build a tank circuit with a 1:8 air core transformer and a 9-50 pF variable capacitor.
After another hard days work at school I went to the parking lot to do some initial tests before going home. I shot this impromptu video with my phone to show you the result.
So I built myself a Full Wave End Fed! It’s not supposed to be like this! With the 10 meter wire I got the same result: on 20 meters I got a dip, but the SWR wouldn’t get below 2.2:1. I didn’t check the performance on 10 meters, but I guess I will get a near perfect SWR there, too. Of course, on my workbench, using a 3300 ohm resistor as dummy load, I had no problem matching 40 and 20 meters.
I’m a bit baffled and unsure what to do next. I already tried some transformers using ferrite cores from my junk box, but non were giving me a tuned tank circuit (inductance too high). I want coverage from 40-20 meters and my capacitor has a range of 9-50 pF. The inductor should be 11 uH then and with a 1:8 ratio the transformer should make 3300 ohm into 51 ohm. The only thing I can think of right now is that my wire is not suitable, but why? As I said in the video, any suggestions are welcome. In the mean time….I’ll keep studying about EFHW antennas.