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On Wed, Dec 13, 2023 at 10:40 AM, John - KZ4AX wrote:

I use end fed random length, not resonant on any band. ?I need to get a 9:1 unun to see if that makes ol’ random wire ‘work’ better.?

It may or may not work "better", but here's the theory. With the right random wire length (kind of an oxymoron, if you ask me), the impedance ends up being close to 450 ohms on the bands of interest. The awesome tuner in Xiegu rigs can go ahead and match that just fine. But a 9:1 unun will bring it closer to 50 ohms. It'll be a perfect match on a band or two, and often 3:1 or less on all the others, making the EFRW a great antenna for rigs regular tuners.?

Here's how you test the theory: attach a 450 Ohm resistor across the antenna and counterpoise connections of the unun (no wires attached) and check the SWR with a NanoVNA or your favorite analyzer. If the unun is made with iron core material, you will see a steep drop just before 40M down to nearly 1:1 all the way to 10M and beyond. The iron core's efficiency drops off quite a bit below 40M, which is why the EARCHI design rightly states that it is for 40M - 10M. Does it work on 60, 75-80, and 160? Yes, but the losses increase exponentially.?

You?can?make one with type 43 ferrite cores like the FT82, FT140, or FT240. Heck, you can liberate toroids from old monitor or power cables and use them too. Your subsequent test will show a much flatter SWR down to 2 MHz.?

So, back to the question about whether it'll work better, yes - it will in cases where you want the antenna farther from the radio, like up on a pole or attached to a building. Coax losses begin the enter the equation, so quality coax is better that RG316 or RG174, but anything will work, and the improvement from greater height will almost certainly be far greater than any coax losses.

In any case, though, a counterpoise is highly recommended. You?can?rely on the shield of the coax to do this, provided it's at least 16' long. Some common-mode currents will be present at the transceiver. They may be trivial, or they may cause weird, wonky issues. For that reason, using a 1:1 common-mode choke at the rig-end of the cable is a good idea. It can be as simple as 12 turns of coax through a type-31 or 43 mix toroid.??

I encourage?all?hams to experiment with antennas like this, and also to build their own transformers. Look through your junk box for laptop power bricks or old VGA monitor cables and carve out the suppression core. Check it at two points with an ohmmeter. If it shows no continuity, it's probably type-43, which is perfect. If it shows?some?connectivity, it's probably type-31. It will not work great for antenna transformers, but you should save it for a home-brew current balun. Save the wire from the cable to wind the transformer.

with the plans. If you build it correctly, it will pass the 450-Ohm resistor test. Head out to the field and try it with the recommended wire lengths. IT WILL WORK!. Frankly, you will love it, and you'll get a tremendous boost of satisfaction for doing it yourself, especially if you use scavenged wire and cores. This is one of the most satisfying aspects of our hobby!
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73 de K9NUD