I’ve tried a few times to build my 2nd EARCHI UnUn/Balun/Transformer in a nicer box and use 18 gauge stealth wire.
I read http://www.webclass.org/k5ijb/antennas/End-fed-multiband-antenna-BalunDesigns.htm as well as VE3EED and several other sites and decided to make my antenna 53 feet since that is supposed to be shortest/best.
I also read this guys site which gave me an idea to actually bench test the transformer after my failed attempts to achieve some resonance.
So I constructed a 330 resistor connected in series to 3×330 resistors in parallel to make up 440 ohms. I needed 450 ohms but I only have 330 ohm and 10K ohms from my Arduino starter kit.
I tried to test out the resistors via my cheap multimeter that came with my cheap amazon soldering kit but the readings were all over the place so I hooked up my nanoVNA directly to the SO-239 connector on my UnUn while the resistors were across the antenna input + ground.
As expected, I’d built the UnUn correctly. The resistance throughout the whole HF range was about 50ish ohms and the SWR was less over the same range.
W5KV is a big fan of saying you should test at the antenna (to remove false readings when testing thru your coax since losses in your coax will falsely change your SWR). I remember that being a question in the General exam I think. Anyway, I like to test at the radio since that’s what my radio sees (unless I use my ATU).
Here’s his YouTube: https://www.youtube.com/channel/UCk2gD-0yd6GJ1Dh2-7Ko5kg
I suspected my old 50 foot coax was bad or suspect since bunnies had bitten into it in several areas so I tested some newer 1,3,25,50 cables and they all tested identical to my VNA being directly connected to the UnUn. I tried my bunny-bitten coax and it tested the same after making sure the connections were tight.
So that removes everything from the equation except wire length which is the most annoying part since its difficult to set via bench test since everything depends on the wire’s environment.
Its also funny because everyone says you need to use a tuner (which I do with my attic EARCHI) but according to the numbers everyone posts with SWRs in the amateur bands being less than 2, I wonder why an ATU is needed? I’m happy and don’t use an ATU with my MP1-C at 20 meters all day every day.
So I guess its back to the drawing board with the length. I’m guessing I need to look up the velocity factor of the stealth 18 gauge wire and see if I can compare that to wires others are using.
I did get satisfactory SWRs somewhere between 40-45 feet with the exception of 40 meters. I’d like to get it under 2 on 20 and 40 since I want to minimize the amount of equipment I have to haul down to the kitchen where I usually get on line since there’s a nice view at the kitchen table.
Maybe I need to just make my “go box” using a milk crate and stop complaining about brining my 7100, atu, (power supply or LiFePo4 battery + solar panel), and log book in one trip. But that’s another post.
73,
KF0BBY
