I’ve got a question about using a random end-fed wire fed through a 9:1 UNUN and a length of coax. Someone is even selling a commercial version of the antenna here: https://kx3helper.com/endfed-40-6m-antenna/
Isn’t there going to be a lot of loss in that 25ft length of RG174 due to high SWR inherent to that random length design?
I’ve seen tables of suggested wire lengths (see below) but I have no idea where they pull those SWR figures from because a simple 9:1 UNUN is not going to result in those SWR’s. Someone please enlighten me.
Perhaps I need to deploy one and measure the SWR, although I’d improve it by using a type 61 ferrite core instead of EARCHI’s iron powder core.
“The EndFed 40 m to 6 m Antenna is arguably one of the best field antenna choices you can make for QRP ops and is especially well matched with the KX3, FT-817, the KX1, and any other QRP rig with a tuner”.
Hi Barry, I’m not sure that I can enlighten you, but I’ve pasted above a quotation from the website that you linked, which mentions “any QRP rig with a tuner…” so maybe the SWR is measured between the rig and the tuner, which would help :o)
Yes, I understand a tuner is absolutely necessary. But how high is the SWR on the feedline between tuner and antenna? And doesn’t that mean potentially high line losses in the coax?
I’m not yet ready to believe in magic, i.e. those SWR numbers in the wire length table I posted. Those SWRs must be post-tuner, not pre-tuner or ??? They can’t be the SWR on that coax feedline.
My own measurements with a PAR-ENDZ 10,20, 40 have the SWR better than 1.3:1 for 20 and 40m.
If I’m planning to use a full range of frequencies then I use my LINK-Dipole which is ~1.2:1 or better on all freq planned… 20, 30, 40 & 60m, no tuner needed… and KX3 tuner will match on 10 and 80M…
And those are precisely the numbers I’m questioning as absurd.
And Richard, the PAR is a resonant half-wave. This is a TOTALLY different animal. Let’s please stick to random length wire antennas fed through a 9:1 UNUN
I’ve read those before and they don’t really shed light on what the real SWR on the feedline is. They deal mainly with the transformer itself. The best xfmr isn’t going to erase high SWR on the feedline if it’s present.
It shows the measured SWR without a tuner for a wire length of 41 ft (scroll to the last page to see the table). What isn’t clear is if the measurements were made at the matching unit or at the end of the feedline. I only make measurements at the matching unit/antenna as the SWR readings will be lower at the other end of the coax feedline due to losses.
In any event, nothing magical about a non-resonant random wire antenna. The SWR will be high on certain bands depending on the wire length you choose. I see that W1SFR suggests the SWR on 30m with a 35 ft wire will be 8:1. Its been a while since I tried to calculate the losses on a coax feedline based on antenna SWR. However, I remember the ARRL site has some good tables to reference that will give you a good idea.
I’ve never tried using a random wire antenna for SOTA but I know WA2USA does with good results. I believe he uses a separate counterpoise wire and I forget how long his feedline is…probably really short!
I use a home made EARCHI Unun. The toroid is an FT50-43. The enamelled wire is 0.3 mm.
The feeder is a 8m long (aprox 22 feet) RG-174.
The antenna wire is a 0.3mm² (approx. 22awg) from Sotabeams.
It was used as a long wire as an L, sloper or horizontal.
The wire is rolled in a wire winder and the length (random) is adjusted to fit the available space. Started as a 41m long (134.5 feet aprox) but after 100+ activations it’s shorter (some tree entanglement…).
The results are awesome!
Some QSOs with VK and ZL been almost usual across the pond.
I had use it with KX-1, KX-2 and KX-3 (all with ATU).
Yes, agreed that random wires work fine with counterpoises and very short (or no) feedlines.
I’m pretty sure he measured those SWRs at the end of 25ft of coax. I agree with you that you need to measure SWR at the matchbox. The numbers at the end of the coax are almost meaningless unless you do the Smith Chart reverse calculation etc. If I get inspired, perhaps I’ll do some measurements at the matchbox.
Malen, if you are going to try and use this type of antenna, wind the transformer with a type 61 ferrite core (8 turns). Some of the links above discussed why this is the best choice.
I’m not sure why activators would want to carry a long coax feedline, counterpoise wire, etc. I realize the guys that want to put up dipoles need to do that. I’m glad I abandoned dipoles and now use an EFHW. My feedline is really short and the only reason I have that is to have more flexibility in my operating position on the high summits. I’ve always used resonant antennas as I didn’t want to carry an external tuner. I now have a KX2 with internal tuner. I can now tune my existing EFHW to more bands without making a new antenna ;-).
Sorry for the brief sidebar Barry! Back to the topic…
