Making a 49-1 Un-Un (Not A Balun) For End Fed Half Wave Antennas

[@TheSmokinApe]

Hey John, one way to test it is to run a resistor accross the element lug and the ground lug, 2450 ohm. Sweep with the vna and you can see if it transforms the impedance, they will tell you how well it transforms, not efficiency or loss measurements 👍

[@A.R.O.T.A.]

I know I don't have that value on a single resistor but I may be able to do it with 2. I'll try it later.

[@D3n3ys]

@@A.R.O.T.A. look at ape's vid from 17min into the video kzbin.info/www/bejne/gaaocoyhpZKgos0

[@D3n3ys]

I have found this as well. Quite interesting w8ji.com/balun_test.htm it is a bit more involved

[@daviddunn148]

Just made my own 49:1 after looking at countless videos of how to / how not to make one. The one thing I found out is that no matter how I wound it I could not get the SWR down below 15m which is okay as I don't try 10m very often. Another thing is I could not get a good reading on SWR/Impedance UNTIL I cut all the leads, terminated them in the box. Then when I put a 2,450 ohm resistor across the antenna connector the DIY 49:1 swept below 2:1 SWR and stayed at 50 ohm from 160m to 20m then the SWR went to about 3.5:1 and 100 ohm for 15m. Keep the windings tight, be sure to count the first two of the secondary as the first two of the primary windings or you'll have too many windings in the secondary. No matter what gauge wire I used, #18, #14, #16 etc. the 49:1 seemed to act the same. I also found that to get the two color wire, #18, I used solid core thermostat wire.

[@A.R.O.T.A.]

The 49:1 & 64:1 are both designed for half wave long wires and as a result some bands will not have a good SWR due to them not being harmonically compatible. However you may be able to get them to work with the the addition of a tuner but if your going to use a tuner a 9:1 Un-Un and a random wire would probably be easier.

[@cthoadmin7458]

Be interesting to see a sweep of this on an antenna analyser... Interesting to see an EFHW transformer and the choke in the same box... must try it. 73 Tim.

[@A.R.O.T.A.]

Placing the choke in the same box prevents the coax acting as part of the antenna so it doesn't act as an additional counterpoise.

[@A.R.O.T.A.]

The following comments were added to the link I shared on the Facebook group "UK Amateur Radio" Jim G7NKS probably one of the most misunderstood and underrated antennae ever! With an easy to build 49:1 transformer and a half wave length of wire you get an easy to lash up performer that will work on pretty much all half wave multiples above the base design length PLUS because the feed is at high impedance, the current is low and so only a very simple short counterpoise arrangement (~ 0.05 lambda length) is needed. You WILL need to build and add in a common mode choke on the feeder, ideally ~ 0.05 lambda after the feed point on the design frequency, as the design inherently has RF on the shield but a choke is very easy to make too. Get winding, add in your 100pf high voltage cap, bit of soldering and away you go! Vertical, horizontal, Inverted V, L pretty much any configuration will work (with bounds of common sense!). As you go up in frequency from the design freq, the radiation pattern moves to be more in line with the run of the wire as opposed to the traditional broadside, so if you build 2 EFHWs and mount them at 90' to each other then you can get global coverage on your design frequency and each half multiple up. They even work fairly well on the non-multiple WARC bands albeit needing an ATU perhaps. Mounted at lambda/2 high on the design frequency or as close to that as you can will give you a reasonable medium to low angle take off if horizontal and so fair to good for Dx. virtually invisible if right colour wires are used and transformer box painted to blend in. Why more people don't use these has always baffled me! Yes, if you have the space and £££ then build the mast and shove the Steppir on top, but back in the real world, the EFHW kicks butt (which is why the military use them!). John M7CPT That is one terrific comment. You mention using 100pf high voltage cap. The 100pf cap I had to hand was not high voltage would a high voltage cap really be needed in my case running only 10w max? Jim G7NKS John Cressey thank you for the kind words. I'm no guru on EFHWs and there's many on here way more knowledgeable than me. As high voltage caps are cheap as chips, i find it is better to build with a high voltage one and then you can go QRO if you want. Your "multimode" unit sounds great too. I've always gone for a simple approach as I'm not the sharpest cat in the box so have just built numerous 49:1 transformers with various types of wire and ferrites to see how they behaved when fed with QRP to 26dBW! I've had success and smoke, bangs and contacts! Like you and many of us, I have limited space and neighbours I want to keep friendly with and my best "axis" runs East-West so radiates N-S! doh! however running a 40m long EFHW cut for 80m on that E-W axis does give me decent lobes at 35 degrees and 55 degrees to axis on 20m and up so for those bands its fair for the US, South America etc. Common mode chokes, for me at least, have sorted 99.9% of my noise and EMC issues, so now my PC and internet don't melt down when I transmit and I don't get burnt fingertips!! Good note and thanks again! Jim G7NKS. Feel free to copy and paste my comments etc and use them as you wish, its only my ramblings!

[@W0KNI]

For your first attempt, that's a really good build John, congrats! Combining the 1:1 CM choke and a transformer in series is definitely an advanced project! (fyi - your CMC is not a balun, but a transformer that cancels out the reflecting current when moving through the coils, semantics to some but if you test a CMC with an analyzer and a 50 Ohm load, your Z should be flat). Looking forward to your follow up video!

[@A.R.O.T.A.]

I do have another method to cover the 1:1 CMC and some other interesting designs for switchable Baluns to come before this set is complete. Hopefully I will be able to find a UK supplier of the PTFE as it can take ages for it to arrive from China.

[@ae1tpa92gwtom2]

Nice one mate, I often thought this is the appropriate way to build an EFHW, Im constructing one now and may chng my project after watching yr video, I have subscribed to yr Channel, 73 n gd DX

[@A.R.O.T.A.]

Thanks I'm glad the video helped.

[@philwright5970]

Its an impedance transformer

[@twohandsandaradio]

Wonder what performance difference there is in using insulated wire and magnet wire?

[@A.R.O.T.A.]

I don't think it would make any difference providing you remained within the frequency rang and power rating of the toroid. However if the toroid generates heat due to being used out of frequency or too much power the enamel will burn off at a lower temperature than the melting point of the PTFE insulation.

[@A.R.O.T.A.]

I have just done a video on making a different version of a 1:1 balun (Common mode choke) that uses PTFE coated coax and the results shocked me. It appears the answer I gave you may have been incorrect. I will be doing a video soon as part of the balun playlist comparing the 1:1 balun with the PTFE wire, PTFE coax & Enamelled copper wire.

[@A.R.O.T.A.]

Your question will be answered in this weeks video on #MNHR I will compare 3 1:1/common mode choke baluns made from PTFE wire with magnet wire and PTFE coated coax. The results are worth seeing!

[@jamesgeorge1709]

I don't understand why you put the RF choke on it, that defeats the operation and now will require a counterpoise wire. ????

[@A.R.O.T.A.]

I added the choke to get more accurate results when testing ideal counterpoise lengths and ground rod efficiency.

[@arlindotelles857]

Is it possible to build a balun for an EFHW antenna without a ferrite core or feed that kind of antenna without a balun? I've tried a Zepp Antenna without success since I dont have an antenna tuner, just an old FT840. Thanks!

[@A.R.O.T.A.]

Not to my knowledge but I could be wrong. I am relatively new to amateur radio.

[@A.R.O.T.A.]

You may find this video by Dave Castler helpful:- kzbin.info/www/bejne/eaqcc3ueet2Cjc0

[@A.R.O.T.A.]

I've just been looking into the Zepp Antenna, as far as I can make out a 1/4 wave of 450 ohm ladder line feeding a 1/2 wave antenna from the end should work with a 1:1 balun. If this is correct then a dirty balun (Coax balun) might just do the trick. kzbin.info/www/bejne/o3qopY2kfLicnKM

[@johnrees44..G4EIJ]

Excellent video..Thank you.. John.. G4EIJ

[@A.R.O.T.A.]

Glad you enjoyed it

[@gfl1957]

This is not a balun. It is also not an unun. It is an autotransformer.

[@A.R.O.T.A.]

It not the name that's important but what it does. It's useful and required for an EFHW Antenna but I have been informed that in some cases a 64:1 works better better and there is also a 4:1, a 9:1, two versions of a 16:1, a 25:1 & a 36:1 that can also be of use. Needless to say my Balun/Unun set is not as yet complete.

[@paultemple5566]

Check TRX lab for his series on chokes and transformers....great info and testing regime

[@renaat9829]

100 pF and at least 500v 1 Kv is better

[@A.R.O.T.A.]

I did end up changing the cap for a high voltage one in a later video.