Why is it showing a Short Circuit. 49:1 Transformer EFHW

[@pa6552]

Man, this is a life saver - was busy re-cabling my rigs and for some reason I tested my cables and found a short on the EFHW. You saved me a very arduous trip up the roof! :)

[@mike-M0MSN]

Glad I could help

[@pa6552]

@@mike-M0MSN I'm hoping you could clarify something else for me too please. Since the EFHW has a DC short on the cable, does this have any potential effects I should be aware of when bonding my different feedlines? I have 2x UHF/VHF Antennas using LMR-400, and then one feedline - RG-213 for the EFHW. If I understand the whole grounding/bonding thing correctly, then all the shields from all my feedlines are basically electrically connected when bonded and connected to common ground. Does my VHF cables shields then also act as additional counter poises for the EFHW? Should I/ Can I have them all connected at the same time to different radios and TX/RX simultaneously, or would it cause issues?

[@gloves1212]

Your tap off method made this possible for me, I improvised with the speaker wire I had and the twisted pair version wouldn't wind nicely in my small toroid, but the tap off is perfect! Now my SWR is great on my EFHW 11m, cheers!

[@mike-M0MSN]

Glad it helped

[@ben2e0omr]

Great video Mike. Reinforcing previously gleenend knowlage and theroy.

[@mike-M0MSN]

Thanks!

[@R50_J0]

The first video I've seen in months were the background music level is set perfectly.

[@mike-M0MSN]

Thanks Louis

[@Andy2e0ree]

Great video Mike keep up the fantastic work bro

[@mike-M0MSN]

Thanks Andy Bro: Appreciate it!

[@dback4430]

Ok that was informative. Didn’t know about the tap version. Now I want to build it to see if there is any difference at my qth. Thanks

[@mike-M0MSN]

Go for it. :)

[@dback4430]

@@mike-M0MSN so if the tap method works great, what was the reason behind the twisted version. Also where do we make requests for videos ? 😁

[@frequencywatchers]

WOW! Just Learned Few New Things From This Video Alone, What A Great Library Of Videos You Have On radios And Waves, Thank You Mike. :) Subscribed From This Channel To :)

[@Oldnoitall]

Now I know what the compasiter is doing ! oTried mine today! 66’ wire maybe 8’ high at the ends and was S9 into Onterio from east Tn USA.

[@dixsusu]

Hi Mike . If i may ? For those who still this is magic , the short exhibits only for DC voltage/current , the voltage/current which our transceivers use to radiate electromagnetic radiations in antenae a.i diferent wavelegnth on amators bands but not only are AC voltage/current . In AC there is no short , are matching and mismatching , frequency, antenae models and feeders types dependent .

[@DXCommanderHQ]

Perfect.. Now do a magnetic loop Mike! :)

[@mike-M0MSN]

Cheers DXC, I think Kevin Mc has got there before me, still worth doing!

[@Kevin_KC0SHO]

First off, thank you Mike. Your videos are very informative and have helped me understand concepts which are normally only glazed over by many other videos and documents I’ve read. I’ve attempted to build an EFHW using the DX Commander 10M pole and a 49:1 Palomar transformer with no success, and I’m a bit lost. I also purchased a 64:1 from Cal that you made for him. I’ve only used my Comet SWR meter thus far as I don’t believe the 64:1 would take much power and was going to use it for an RX antenna. For simplicity, I made a 10M 1/2 wave element, which I cut for 28.5MHz both taking into account Calum’s end-effect formula, and without. I’ve used a ground rod, an 8 element radial field, both, and none. I only wanted to use a single band, in this case 10M to keep it simple. I also attempted a 20M 1/2 wave, cut for 14.250MHz, with no success. The issue is my SWR is off the chart, no where close to my tuned cuts. I’m using a 3 foot jumper from the antenna to my meter. I’m going to use the entire length of coax which is around 150ft or so. I also plan to use my VNA and shoot the coax for length just to understand what I’m dealing with. Also my meter and jumper work great when testing my DXC 12.4 which uses 1/4 wave elements as spec’d by Calum. Summary: using a 49:1 from Palomar, or your 64:1 with a ground rod and or radials, my SWR is infinity on 10M, but its in tune tune at 14.4Mhz, which would a 1/4 wave on a 4.95M long element using DX50. The values for R and X from the meter are below. R=5 X=44 SWR=♾️ Any ideas Mike? Thanks

[@mike-M0MSN]

Hi Kevin, yes I can help, first the 64-1 unun, is made for 80 - 10 meter bands and needs to have a wire length of at least 20M (then cut to SWR) unfortunately it will not work with shorter lengths of wire. (If you use 20M of wire you will have 40, 20 and 10). So here is was you can do with the 64:1 if you only want to work 20M and 10M: Open the box and remove the last 2 turns or if you find it easier scrape the coating off the second winding from the end and solder a new wire from there to the antenna terminal. this will turn the 64:1 into a 49:1 which will work better on the bands you want to work on. hope this helps Cheers Mike

[@Kevin_KC0SHO]

@@mike-M0MSN Thanks Mike I appreciate the response. At one point during the testing, I did connect a 49:1 Palomar Unun, Model: CU-49-2000HF, and the values for Resistance and Reactance were as follows: R=5 X=44 The 64:1 Unun showed the same values at 28.5MHz. I would expect these to change a bit, which is where I began to check connections for continuity which all seemed fine. I'm a bit confused as to why the Resistance and Reactance are not changing from the 49:1 Palomar, and the 64:1 M0MSN Unun, but I'll dig some more. I'll validate the SWR reading with the Palomar 49:1 Unun, using the full length of coax which shows to be 57.42M according to the Lite VNA 64. I don't want to tamper with my Mike Unun just yet, lol. Thanks again Mike.

[@hennero.3826]

Thanks for the video, Mike. 🙂 I just built such a 1:49 transformer last night and have not yet had the opportunity to attach a half-wave wire as I need to do that outside and operate portable (cannot do that at my apartment). Therefore I do not know if it actually works. However what I have done to get a first indication if the transformer does what it is supposed to do, is attaching a purely resistive load of ~2400 Ohms and then measuring the inductance and the SWR over 3..30 MHz (the range the my NanoVNA supports). I found that a reasonable SWR (~1.34 : 1) was only shown at the start of the range, increasing steadily from that point as the frequency increases. The inductance at 3 MHz was very close to purely 50 Ohms with nearly no reactance. Is that how it is supposed to be, I mean, is that normal and is it likely that once I attach an antenna wire and a counterpoise I will get a good SWR on the band I want (provided that I trim the wire length accordingly)? Or does the above-mentioned obervation with the low SWR only at 3 MHz indicate that there is something wrong with my built? 🤔 (I am a newbie and my tinker box does not contain any wire to test, so I am waiting for the antenna wire to be delivered, being slightly worried that my transformer is not built correctly.) 73 de DO1HNR

[@mike-M0MSN]

No it just lets you know that the impedance of the resisters changes with frequency, the impedance at the end of the wire is between 2400 to 3600 ohms ....so get 20 metres of wire out and fold back the end to get the best VSWR. good luck

[@markramsay6399]

Fascinating Mike - really excellent resource, thanks! How is the heat pump coming on. Mark.

[@enginedave]

I always remember my Elmer's words: RF doesn't recognize a DC short

[@mike-M0MSN]

yes, unless its in the coax. lol

[@robertbird7297]

Thank you for explaining how an impedance transformer is wrapped. I would like to know what is the value and rating of the added capacitor ?

[@smstiao-tecnologia]

Good job Mike! 73 to PY2SNN.

[@alangoulding4252]

What was the value of the capacitor Mike...brilliant informative video.....

[@ronbo422]

Mike, I really like watching your build videos and this one, for whatever reason, punched thru my cranium to where I understand how the 49:1 works. Have you built 4:1 Baluns, for loops? There's a 2.5:1 balun, known as the "Talented Balun", that is supposed to be spectacular. The reason, as the ham who markets that balun says, is a skyloop antenna is actually 125 ohms, and a 2:5:1 balun, not a 4:1, is perfect match for 50-ohm coax. Thanks for the videos and the work you put into them.👍👍

[@erikdevriese671]

As I understand it it doesn't matter wether one uses an intertwined secondary winding to connect to the center wire of the coax or wether one uses ust a tap (soldered) connection to it. Because for DC there is always a connection to earth (or counterpoise). Does this mean that if I use a real earth connection (via a copper rod driven into ground) that I also have some lightning protection? Tnx for your valued input and 73's

[@michael_KD8GIJ]

Very nice explanation. Would you think about making a video discussing the selection of the capacitor for the EFHW, how man pico farads and why? And, if it doesn't matter much, why (or why not)?

[@mike-M0MSN]

Yes I may do that.

[@kevinkc3onohelijeepworld953]

Mike have you ever tried a 3x wavelength end fed ?? With say a 64:1 or greater balun ? My buddy is running one on low band with a parasitic radiator below it at 60’ height I believe in a inverted L shape and with 1k he does pretty well. He’s not a DX er so can’t attest how well it works out far 😊

[@mike-M0MSN]

Would have to give this ago, just need the space. :)

[@aarongriffin81]

8:10 You said it is 2,800 Ohms to 50 Ohms but I always built my antennas to match 2,450 Ohms on Mmana Gal. Which is correct?

[@mike-M0MSN]

Well they both work, its all to do with length and height....

[@OhmSteader]

How are the Smith graph radiation patterns produced. Is it conjecture or something that can actually be seen with some kind of instrument or device? I have been able to see the static charge patter on a charged pvc pipe using ashes sprinkled about the pipe and saw the ghost. It was a series of torroids up and down the pipe which can be discharged like individual cells by putting a light bulb or my finger near each one and hear the click as they are discharged. People think I am crazy and asking too many questions which will not even be on the extra exam anyway. I have to wonder if dusting ashes over my antenna array would show me the pattern which I am wanting to see. I have asked Callum & he thought this is a question for you. Thanks for the education. Mike

[@darren2589]

Great video thanks. What value capacitor is that one you used please?

[@mike-M0MSN]

100pF

[@andya940]

Excellent video Mike. When you said that the tapped version works better than the coupled version. In what way does it work better? Thanks

[@mike-M0MSN]

Difficult to quantify, I found that apart from saving copper, the 64 or 49:1 was more predictable I did not need to space the turns as much to obtain best SWR.

[@donaldsmith3048]

I like that. 2 toroids and a large wire. How much power do you think that will handle? I have some 240-43's and some 14 gauge wire, not sure what that is in mm. But it is about the size you have there. I am not sure if I should use 2 or 3 toroids. 73 W4DES

[@32_bits]

Lots of good info for winding the 49:1. Some question for the earthing, if a stake or counterpoise is used what difference do these make? And in your 1st diagram where the windings are sepatated, if the aerial side is earthed but the coax side is not, does this work better?

[@mike-M0MSN]

Hi, the base of both coils/windings in Dia 1 are connected to the Shield if you don't there is no circuit. as for the counterpoise/earth stake if you use them it will reduce the RF on the outer part of the Coax and prevent its return to the shack and also reduce noise.

[@JayN4GO]

Great presentation. I’ve always thought the coil was needed at 2.1m up the radiator. Some people have used long counterpoises. Essentially creating an ocf or half square with these. I’ve never noticed any real differences doing that other than throwing the swr into fits. Have you used long radials with the unun?

[@mike-M0MSN]

Hi Jay, thanks for the post, one I have never used radials on the EFHW, sound like an experiment needed.

[@njjensentube]

Great presentation Mike thank you ... on the VNA test , what did you use as terminating resistor ? Or was this test on the antenna it self ? Also wondering if you have done any efficiency tests ? Thanks Niels / OZ1CGQ

[@mike-M0MSN]

Hi Niels, I guess you mean to calibrate the VNA, I have a calibration kit that comes with a 50 ohm short SMA. if you mean the antenna then I did the test on the antenna after a calibration on the VNA. and no efficiency tests.. :)

[@njjensentube]

@@mike-M0MSN thanks Mike. I am working on 49:1 as well. I got the efficiency to exceed 90% on most bands except 10meters. It takes 2 UNUN in series to make the measurement, and then divide results by 2 It’s very interesting because you can play around with different designs / ways to build UNUN … and understand how performances can be improved compared with “standard” way of building UNUN’s

[@MikeG-js1jt]

what were the size of those 43 mix toroids?... or maybe you have a link right to them?

[@mrkultra1655]

Thanks

[@mike-M0MSN]

Welcome

[@kf5hcr176]

Autotransformer..... I wonder if a variac would work?

[@bradpeterson2953]

Hi Mike, Ive just bought a Nanovna and im wondering what software you are using when connected to the pc? Thanks.

[@mike-M0MSN]

VNAsaver

[@adilcetin9080]

Hi @mike-M0MSN, after this video, I decided to create a new 49:1 Un, and I used 2 pieces of 240/43 Amidon Troid in the beginning of the winding, using a single winding, just like you, without using double wire, using the wire used in 2mm enamel-coated copper windings. I created a beautiful Flour with , and since the thyroids did not fully kiss, I combined the Troids that I leveled with sandpaper on the glass, and after covering the Troid ring with heat-resistant teflon wrapped around the taps and a few turns of teflon, I created the winding. I combined it very well, but even if I used different lengths of wire in Nano VNA. SWR is affected very little, SWR is infinite in the bands I want, when I make broadband measurements between 100Khz and 1Ghz, SWR 1.0 at 700 MHz, when I measure between 100Khz and 100Mhz, SWR 1.1 at 67.1MHz, and when I measure between 100KHZ and 30MHz, SWR 1.1 at 1.150Mhz and 5.800Mhz. Swr 1.1 at Hz Without grounding the measurements are worse, a good ground connection is required. Listening on CB is very nice. I did not do TX because SWR is infinite. I wanted to do a different experiment and created a connector from UNUN's chassis and antenna end, which I used to connect the antenna side to the radio, and made a reverse connection to the radio. I connected the antenna to the input end. SSB also provides zero interference and perfect listening. When I try to connect the capacitor, it weakens the listening and the interference rate increases. It amplifies, listening without a capacitor is great. I'm trying to understand my problem, it was built with 2mm enameled copper wire in the same way as yours, the only difference is this, do you have any suggestions for me?

[@mike-M0MSN]

If you copy my build as I have made it do you still have the same readings, It maybe something you have introduced to the build or the torrid rings being used, I wish you good luck. and many thanks

[@adilcetin9080]

I bought the rings from the Amidon manufacturer in 6 pieces as part of the campaign, the rings were ordered from the right place, the only difference is that I created them with 2mm wire and combined the rings by leveling them with 0 grit sandpaper on the glass surface to ensure a perfect kissing.

[@T.M.G2014]

do you make and sell these at all

[@cthoadmin7458]

Why the hell don't my end fed transformers ever look as good as yours Mike? Must try the tapping version...

[@mike-M0MSN]

lol

[@sstorholm]

I think I’m slowly starting to understand how these transformers are wound. Question, in a power transformer, increasing the amount of turns improves efficiency, is it similar with RF? Aka, would a 200 to 1400 turns transformer perform “better”, and in what regard? Increasing the wire gauge improves current capacity, and increasing the toroid size improves efficiency, but what does the amount of turns do? Another thing I wondered about is what would happen if you increase the insulation thickness (for example if you’d use normal single insulated house wire), and if solid vs stranded vs litz wire affects things? 73 OH6ZA

[@mike-M0MSN]

Good question, I guess it all about diminishing returns, is the extra 7 or 8 turns of copper worth the small improvement if any? any more than 3 primary turns may over couple, sure the bigger wire and the core the more power you can put in, however the more space you create between the core and the wire the less efficient the transformer becomes. Its all bout the electromagnetic flux....back to the future Marty

[@BusDriverRFI]

So it's a DC short and we don't care since it's not an AC (RF) short. But what is it? What is the total unloaded input impedance of the desired spectrum?

[@mike-M0MSN]

Not sure I understand your question?

[@BusDriverRFI]

@@mike-M0MSN When you look at the XL of the input with no load on the output, what does the nanoVNA show the 2 input windings to look like over the desired frequency range?

[@mike-M0MSN]

@@BusDriverRFI I have no idea, I will connect it up when I next have reason to take it out of use and measure it for you. However if you already know or are building this transformer please share your knowledge here. Cheers.

[@BusDriverRFI]

I don't know. I feel like it can't be much since 2 windings is pretty small. Seems like a point where there is a lot of loss. No, I don't have any 49:1's.

[@lancehollingworth4043]

Hi Mike... The thing I can't get my head around is - back end of the 70's early 80's on CB as a school leaver, the threat of a pin through the coax to blow a wally's rig up was regarded as a true fact? Fast forward to today, with a full licence, that back then believable true but untested fact has always stuck with me and I can't compute how a direct short on the first 2 windes of the transformer doesn't do the same as it shorts the centre to the braid just like a pin through the coax would? OR was that just a myth from people who thought they knew more than they did?

[@mike-M0MSN]

Hi Lance, no myth, the pin through the coax was and indeed is still a very real threat. You need to look at the 49:1 as a transformer- the power from the rig is passed down the coax into this 2 turn coil and from the 2 turn coil into the 14 turns of the secondary coil, the transformation or transfer of power is call inductance and this is one of the properties of AC. because there is a place for the power to go it will not damage the Rig. But, take a way the secondary coil and it will act like the pin in the coax, there is no where for the power (RF energy) to go, so it returns back to the Rig and creates heat and in a short time "pop" no more rig.

[@lancehollingworth4043]

Cheers for that education Mike - That 2 turns foxed me for a long time.. it still does tbh, I always said to my Ham friends, I'll not go from an M6 to a 2E0 till I can understand 1:1, 4:1, 9:1, 49:1 or any other combination - anyways I did my 2E0 and still had gaps in understanding, even through Bath, and they explained it really well I struggled and funnily enough got all the transformer questions right in the full exam - I've watched 100's of hours in both transformer and inductance. magnetic fields, back emf, eddy currants, saturation, loss of magnetic flux through heat, permeability of cores, mix of cores, the maths involved... And yet, the first 2 turns looks like a direct short at .95% the speed of light to me before the AC can progress to the other turns on the ferrite toroid - kinda like a circuit breaker tripping faster than you can get a shock? I also know the 2 wraps of wire are actually joined to the other windings in 1 wire so I suppose the volts of AC would energise the whole toroid instantaneously and create a magnetic flux in a flash but in all the transformers I've seen where the secondary is earthed it's usually in the middle... - that may be my problem, I've not seen a secondary tapped 2 turns in? Have yo u got a vid of that? I think that's where I can't compute a 49:1? :)

[@louisbanaszak3125]

ferrite type

[@dback4430]

I do believe he uses 43

[@cthoadmin7458]

43 I believe he uses, though I have experimented with 51 as well.

[@dback4430]

I use type 52 but it’s one core or three cores for some reason. 240 size.

[@M7XCB]

He is using FT240-43 in this video

[@mike-M0MSN]

Yep I used 2x 43mix 240 size