I have listened to similar theories all of my life, and have consistently failed to fully grasp them; however, your clear and simplified articulation of this is superior to anyone I have ever heard before. You have actually allowed me to keep up with you and understand. I won't say I'm smarter now, because I wasn't all that smart to begin with, but you, good Sir, have made me less stupid!!! Well done my new friend, well done!!!
You are the greatest!! I love your videos, and your theories!! Next I am going back to the way you wind your cores, to skip the 100PFD cap!! I MUST MASTER YOUR TECHNIQUE! Fantastic SWR, thereafter...a LOT BETTER THAN MY WINDINGS!! LOL!! I hope that you will ALSO do the FT240 series toroids, as well, as I suspect that your winding ratios will, then, need to be modified somewhat.
Perfect timing... I am re-building mine right now. I should watch the video first maybe I learn some new tips that will help me. ( And I did learned ) I did not now that the number of turns affects the antenna depending on it's elevation. That is a great thing to keep in mind for the future.
Danke. Now to go back & re-fiddle my supposed 500W transformer. I have a 150pF cap in the box. Works but I suspect that 100pF may be better. (I’ve found - by way of finding melted plastic in the box - that I needed 3 stacked 2” dia cores and even they got warm at 500W. Which proves that QRP is more efficient ;-). ) 73 de W8IJN
That is the smallest core for this kind of transformer I have seen. This transformer design is the weakest item in the antenna design. There is an old saying that high impedances and ferrite don't mix well. Twisting the wire does nothing useful.
Twisting wire is supposed to help with coupling between primary and secondary. I have also wound it as Auto Transformer, and that worked as well, but I did not test and compare it when just winding primary and secondary in parallel. So you might be right, I just did not test it. So I cannot confirm or deny your statement 73 Manuel; DL2MAN
Your work on the uSDX is truly brilliant, the design is simple and elegant! This post on the EFHW antenna is quite interesting to me. I too have wondered if moving to a larger toroid was actually more efficient or was merely a way to create a larger heatsink to keep the transformer from saturating, I look forward to your exploration of this. I have a few thoughts that you might find interesting. It occurred to me that it would be nice to have a simple method of altering both the transformers turns ratio as well as the actual length of the antenna wire connected to the transformer... These ideas are simple but should result in an EFHW that is still simple while being adjustable for lowest SWR. Pardon my simple math here, I add it in case it will be of some use to novice builders as a reference. I wish I could post an image in this comment as that would make the ideas behind this design immediately clear. --------------------- To change the transformer ratio just add a few turns on the toroid and then add transformer taps so you can choose the best ratio for the antenna in use. Here is the simple math to follow... Take (secondary turns) divided by (primary turns) and then square the result and then multiply that result by 50 giving you the ohms value the transformer will match. i.e. If secondary is 21 turns and primary is 3 turns Then 21/3 = 7 Now square 7 and get 49 Now multiply 49 by 50 and your transformer will match 2450 ohms If secondary is 14 turns and primary is 2 turns Then 14/2 = 7 Now square 7 and get 49 Now multiply 49 by 50 and your transformer will match 2450 ohms If secondary is 24 turns and primary is 3 turns Then 24/3 = 8 Now square 8 and get 64 Now multiply 64 by 50 and your transformer will match 3200 ohms If secondary is 19 turns and primary is 3 turns Then 19/3 = 6.33 Now square 6.33 and get 40.07 Now multiply 40.07 by 50 and your transformer will match 2003.5 ohms If you put 3 turns on the primary and say 26 turns on the secondary and put taps on the secondary windings starting at say 18 turns the resulting matches for each tap will be... tap 26 = 3753 ohms tap 25 = 3471 ohms tap 24 = 3200 ohms this is the common 64:1 tap 23 = 2936 ohms tap 22 = 2688 ohms tap 21 = 2450 ohms this is the common 49:1 tap 20 = 2220 ohms tap 19 = 2005 ohms tap 18 = 1800 ohms Selecting the best tap for lowest swr is easy and you have what amounts to a very simple manual tuner. This can be further refined by making the first several feet of your longwire using something like very small multi-stranded stainless steel aircraft control cable. If you wind this cable onto a spool of some design then you can change the actual antenna length without cutting the wire, the turns all short out and don't create an inductance...if the wire was insulated you would be adjusting both antenna length and inductance and you want only to change length. Using stainless steel cable prevents rust and/or corrosion. If you have your toroid mounted on a piece of plastic as is typical then just cut two slots in the plastic to serve as the spool. This is easier than adjusting the end of your wire by folding it back since the adjustment can be made close to the operating position with no need to lower the antenna. This makes it easy to cover both 80 and 75 meters for example. Combining the taps with easily adjustable wire length results in an antenna for the field that can match any HF band with a very low swr... if you use a spectrum analyzer you will see that changing the wire length moves all the harmonic dips either up or down in frequency. And changing the tap then refines the match lower or higher in relation to the radios 50 ohms. I hope my math is OK, I just used the google calculator and did a quick check on this post, but you can see what I'm doing here :-) 1
This sounds a little complicated to me. Especially because EFHW´s are not in need to be tuned over a wide range. An EFHW works decently even on 2nd and 3rd harmonic. But your theory sounds interesting. Why don´t you build it and make a Video about it ? Sounds fascinating.
Good video! I've been researching EFHW antennas, and it appears that using a Fair Rite 2643251002 core with 14 turns close wound, and tapped at 2 turns, using a 120pf TDK cap, is a lot more efficient on higher HF frequencies than typical 49:1 transformer construction. Its a lot thicker core (~22mm) and smaller diameter than a 240 core (~39mm). Stacking thinner cores along with close winding also seems to help. You might want to look into this if your running much 15m through 10m HF. IIRC its reported to have under 1db xfmr loss, or ~5db less xfmr loss on 10m than typical designs. Its also fine for 100w so it would loaf along at QRP power levels. Apparently thicker cores (or stacking cores), close winding fewer turns, and a high quality cap is the key. Also remember, the more mass a core (or stack of cores) has the longer it takes it to heat up. The more surface area a core (or stack of cores) has the faster it will cool down. If a core (or stack of cores) gets too hot it looses efficiency, your SWR will increase as losses increase. 73 mike
Thank you. I have watched both parts (2 then 1) because I am not conventional🤣🤣. I have the TruSDX and an IC-705 because I am 76YO and money is less important than time and fun😉. Thank you. I appreciate your knowledge and ability to test what is actually true. Channels like yours are very valuable.
Wes Hayward w7zoi suggested there was less loss with type 61 instead of 43, FT-114-61, 3:27 turns, modeling 4.4k load, measured on 40 and 20m. K1RF (gnarc.org/wp-content/uploads/The-End-Fed-Half-Wave-Antenna.pdf) says not to use type 61 "permeability too low!" Maybe a small 43 inside of a larger type 61 toroid?
There are two experiences I want to share here. BTW I have no scientific explanation for this: 1st: I got better results with 2 by 14 than with 3 by 21. Probably a matter of wire resistance, but don’t quote me on that… 2nd: don’t twist the wires of the first windings too tightly. I don’t know how or why… The transformer very probably will work better… Extra: The 100 pF cap must be there. I bought some beefy thick blue 30kV types for just a few Euros.
5W over 50 Ohms are around 45Vpp . 100W are around 200Vpp . If your SWR changes (=not really 50 Ohms), those Voltages can be way higher, and I´d like to have some safety margin.
Thank you for these detailed explanations! 🙂 I recently heard someone suggesting that people who are new to ham radio (like I am) might want to buy their first transformers rather than building them on their own to avoid a potential point of failure. However especially with what you explained regarding how to check if it actually works I am encouraged to build one myself. 🙂Thanks again. Subcribed. 73 de DO1HNR, Henner
Thank you so much for the kind words ! This is the whole idea behind this channel: Take away the fear for the tech stuff ! It´s not rocket science, just radio stuff. Everyone can do it ! 73 and I hope to meet you on the bands real soon ! 73/72 Manuel; DL2MAN
2 года назад
You can try to measure insertion loss with nanovna simply by loading the transformer with a 2400 Ω resistor in series with the s21 port. Resistor loss would be around 33,8 dB, so that should be added to the measured value.
Thanks. Didn´t think abot that. But I will probably built 2 similar Transformers, connect them back to back, so I have 50 Ohms on both sides. Then Insertion loss devided by two is the insertion loss of individual transformer.
2 года назад
@@dl2man Of course, that's another way of measuring, but be careful to make them as similar as possible to get symmetry. You'll probably need at least three of them to calculate insertion loss for each transformer since you'll have a linear equation with at least two unknowns.
I printed a few of your QRP EFHW transformer boards. To make sure i am reading the board correctly, please confirm that: J3, should be RF J4 = ground J5-to-J6 - Antenna Also at the capacitor position there are 3 holes. I used C1 (the two end ones). I presumed that the center one would be if i use smaller size capacitor, in which case i should use C2. Please confirm.
First of all: what do you mean by you "printed" the boards ? Just to be clear: that´s a PCB and no 3D print part.... Regarding your questions: J3=RF, J4=GND, J5=Antenna Side of Transformer, J6=Antenna Wire. Capacitor is 2 footprints in one with one common ground leg. That´s for different sizes of caps. 73 Manuel; DL2MAN
Great first video of the series Manuel and a good refresher! Looking forward to the next one. Why do you not count the "direction change" as a turn? On the one hand it clearly passes through the core. On the other hand it does sit mostly in "air" and not close to the core. 73 de Tobias DL3MHT
That´s an interesting question: My logic was: A very loosely wound transformer will perform way worse compared to a tightly wound transformer. So I assumed: a transition, not even near the inner side of the core would not count as it should have a very low effect. However: I think it can be determined, wether it acts like 3:21(1:7) or 3:22(1:7,33) by simply connecting a variable resistor on the output, tweak it for lowest SWR, and measure it afterwards if it´s closer to 2450 Ohms or 2688 Ohms.
@@dl2man Hmm… Maybe better to compare it to a transformer without turn using the very same core and check what difference it makes relatively? E.g. is 2:14 without turn equals 2:14 with turn counting or not counting the turn on a FT114-43 while trying to keep the spacing similar. With - what is it - 10 or 20% tolerance for the material one could come to wrong conclusions, unless you try to measure the permeability of the core under test beforehand. I guess I try it if I still have enough spare enameled wire laying around here somewhere. Alas just hoisting your antenna 2m higher into the tree or sloping at a different angle makes a much bigger difference.
@@dl2man Found three hours of spare-time and did the experiment: 15 times crossing the inside of the core on a FT114-43 gave me without direction change: 1:56.6 ratio or 2:15.046 backwards calculated. And with the direction change i get 1:50.44 or 2:14.2 backwards calculated. So you were right the direction change only counts as 0.2 turns with my dodgy setup and the way I wound the wire... 👍
What do you mean by "is in short" ? A DC short circuit between inner and shield ? That´s normal, as they are connected via primary coil. When appying AC Voltage (RF) it is not a short. 73 Manuel; DL2MAN
Interesting that, even before you attach a radiating element to that transformer, the SWR is not perfectly 1:1. To me, that means that stressing out over cutting your EFHW antenna to the 'perfect' length where you have 1:1 on 20/40/10m is a waste of time. It's not going to happen, so live with 1.2:1 or even 1.4:1 and be happy. What I am curious about is what SWR is acceptable when using something like the (tr)uSDX that doesn't have a tuner.
In Practice (in the field attached to a wire) I actually found the SWR to be better than on the workbench. I assume this is dependent from elevation of the Antenna and the ground effects surrounding that.
I'm always impressed with your ability to clearly explain things in a second (or third,) language. I've been speaking nothing but English for 70 years and I still have difficulties explaining things, even to myself. :) I've found that if I put the 2 ends of wire about 2 inches apart in a vice (with wooden blocks for padding to hold the wires,) that when I twist the center of the wire it wraps the 2 strands around one another instead of 1 being straight and the other wire wrapping around it. Also, when you are using a larger core you have room to run larger diameter wire, which would reduce the loss in the transformer wire and reduce core heating, (a little.) I'm entirely self-taught, but I don't see any real need to use an NPO type of cap. A few percent drift in value with temperature should have very little effect since it's part of a broadband, not a resonant circuit. (I always use silver mica caps in RF power circuits.)
Thank you so much ! It means a lot to me, as english is not my native language. The NP0 recommandation comes from my experiences with Class E TRX´s. If you use something like X7R/X5R in components that need to handle 5W RF, ehose caps immediately heat up !!! It´s not about the temperature drift. It´s about the Quality of the components in an RF Application. Silver Mica is the level above NP0 ;) So everything is fine. 73 Manuel; DL2MAN
You have 22 turns through the center of the ring. But must be 21. The transition to the other side is considered, because. passes through the center of the ring.
I said it was controversial wether the transition counts or not ;) But I will test the Transformation Ratio with a variable resistor, and confirm or admit when I´m wrong.
Your SWR is quite high. Isn't it because you have actually done a 1:64 instead of 1:49 you have planned? Wouldn't you get better SWR if you connect 3k2 instead of 2k4?
Let´s assume the transition would count as 1 turn: this would be 1:7,333 and 1:53,777 Impedance, so 2,6888 kOhms. The SWR is within expected range (for artificial load). It will be better on real Antenna guaranteed.
@@dl2man ach, you are right. I forgot that we have 3 primary windings so you would have to add 3 secondary windings, not just one, to change the radio to 1:8 :) I wonder, however, why would the real antenna produce better SWR than a dummy load?
