Comparing an Autotransformer winding against a standard winding on a Fair-Rite 2643251002 43 material ferrite core. Digikey & Mouser are easiest supplier to source from. Don't forget that 100pf capacitor (a good one).
Note that the type and thickness of plastic you mount a toroid on affects the efficiency. Without doing dielectric analysis of the plastic you can experimentally put them in a microwave for a set period of time and see which type of plastic stays the coolest, and use that to mount the toroid on. BTW, the very best (most efficient,) end-fed half-wave would use an air-core transformer. A toroid based transformer is just the most compact and convenient, and once you get efficiency up over 90% very few hams will find a need to get any more efficient. As a suggestion, on the step-up/step-down efficiency test I'd suggest you turn the transformers 90 degrees to one another to reduce the chance of their fields coupling and affecting the test results.
Cant believe I have experimenting with Toroids for +1 year now, its an addictive fascinating aspect of the Hobby, have had great success matching, delta loops, and inverted L's too, with the Bonus is the static surge protection is now on the "isolated" antenna side of the transformer and grounded out there away from the house and ham shack, that's an added plus especially with lots of wire up 8n the air as in 80 and 160 meters...
Another SUPER idea!! Colin, I rewound my 3ea.-52 mixture toroids, from the older wide-spaced crossover design to your new auto-transformer design, and it works like a great 'bomb'...(i.e. WONDERFULLY!!)!! I also have the single '102' toroid, with your 1 to 56 design, and it also works FANTASTICALLY, and even though it is the older crossover design. I will NOT rewind that one, as it works so darn well as it currently stands! You sure have blazed some great toroid design-trails of late, and THEY ALL WORK SUPERBLY!! In thinking about the losses, the fact that you have fewer losses not only applies to radio transmissions, but also to low-loss signal reception as well!! My thanks to you, Colin!!
I have tried 4 iterations of different winds using this toroid and the autotransformer winding technique. I first tried a 49:1 wind and a 120pF capacitor. The upper bands were really high, so i added a coil 2m from the transformer and with 7 winds on 0.75” PVC. It raised the SWR on all the bands but aligned them better. I never could get them satisfactorily aligned with a low SWR. I used 20ga wire and an 8 foot 16ga counterpoise. I tried counterpoise lengths from 4-32feet and 8 gave the best. I then tried a 56:1 wind with a 100pF capacitor and the SWR on 40m dropped, but still could not get the alignment i can get with a 240-43 49:1. With the 56:1, same ga antenna wire and again 8ft counterpoise worked best. So then i tried a 64:1 100pF capacitor, all else the same. Could not tune the upper bands at all, but 40m was great and while not aligned 20m was spectacular. So i made two monoband EFHW antenna wires using the 64:1. On 40m got SWR 1.25 center, arround 1.6 on the ends. On 20m, it was 1.17 on each end and at 14.160-14.195 MHz, the SWR was 1.02! The reactance was really low as well. On the other winds the reactance was comparatively high at the lowest SWR. So I am looking forward to see specifically how you tune yours. I am about to decide that while less efficient, the 240-43 tunes much better, but the new Fair-Rite toroid makes one spectacular monoband EFHW antenna. Going to try an 81:1 on 40 next.
Really appreciate the detailed feedback. I've saved a copy. Personally I'm not too interested in multiband options. I like to operate as a monoband with my reel system. I will make another video when I do. Thanks again 👍
As you said, you won't see the 5% improvement on-air. However you may be able to run a little bit more power with the same or less core heating. Thanks for the video Colin.
Hi Colin. Thank you for another great video on the EFHW transformer. I really admire how tightly you made your winds on the 1002 core. I have a very difficult time getting mine tight. At 77+ years old, I am guessing my hands do not have the necessary strength in them anymore. If you or anyone reading this has some suggestions as to a winding technique, I would very much appreciate knowing about it.
Kudos for keeping on going. As a 42 year old I do feel it in my hands after winding a pair. You made a good suggestion for a video, I will ad it to the list.
....going 56:1 instead of 49:1 makes sense, you get a way better match resulting in less loss... trying 49:1 on a 17m EFHW I got 1:1.62 vswr on the NanoVna... OK but it could be better ... I then rewound the core just as you did, auto transformer style 56:1 (15:2) and I got 1:1.04 at resonanance (18.15mhz), that's nearly perfect... I then went key down for 1 minuite 100 watts (didn't want to ruin my rig, the fan was spinning pretty good) and because I could easily access the core I walked over (2 steps) and immediately felt it... it still felt cold. Now I know nothing is 100% efficient but this was plenty good enough for my pay grade.... with that kind of efficiency I feel my 2643251002 core could easy handle well over 250 watts SSB. Colin it doesn't get much better than that...Oh my core is not in a box but attached directly to the antenna; zap strapped to an insulator.. Remember though, we are still (end) feeding a dipole, not a pileup buster, but when not being beaten down by the 2KW big guns.. even with 100 watts, sometimes only 20 watts from my Xeigu G90, you'll work many if not most of the DX stations you hear... I have two EFHW's up in the air...Richard VA7AA/XE1
Great video! I just got ten of these toroids in from Mouser.. cost me like 63 dollars. Also got some TDK 100pf caps. I am going the autotransformer route... the efficiency looks good 160-10. Now I just need to 3D print something to mount them on. I have quite a few 240-43 toroids but have decided to not use them as I don't run more than 100w anyway.. may make up some stacks of three 240-43 just to see how they test out compared to these nicer toroids.. These are heavy and chunky, they feel good in the hand..lol
Nice one Colin, wonder if you could apply the same auto transformer approach to your efficient QRP core and make some further improvements to that - think they were all high but yellow. Really enjoy following your experimentation and findings.
Colin, I've been dinking with Ferrite antennas for 20+ years, the last 5 making ununs using beads at first and more recently toroids. I've been very successful marketing them with nary a complaint. That said, I've been experimenting with the chunky 2001's since you started espousing them. For some reason I'm not able to achieve good VSWR numbers on a consistent basis across the hf bands (Typically not below 1,7:1.on a given band. Some winding configuration will elicit good numbers on one band but not others. This is using a 40 meter EFHW.. My best performer employs an FT114-43 with a 1:30 impedance ratio, 2:10 winding. Excellent VSWR numbers on all bands 40 thru 10. I stack them up to 3 for more power handling although 1 core will handle 100 watts, If you have one, give it a shot! 73, John, ,kg6zbn
John, I ALSO AGREE with your findings. I rewound my 3 FT240-52's from a wide space crossover design, to making it an auto transformer design. When finished, I came up with the very same varying results as you found: ( e.g- my lowest SWR was near 1.1 on 14 Mhz, ..BUT much higher on other bands, especially 40 meters!).
@@MM0OPXFieldRadio Good point Colin. I shouldn't fret over obtaining such low SWR #'s. Modern transceivers have built in tuners that can easily handle the reasonable numbers your's obtain. I appreciate your feedback. Fellow ferrite fan, John
I've built one but so far I haven't got to test it yet. My original EFHW was put up last October. It was put up in a hurry and I expected a lot of the weather proofing to have failed but it was a;; still perfect. So for the time being I have left it. As soon as it starts to fail I'll change over the transformer box and let you know how I get on.
I made one as an auto transformer, 56:1 with a crossover. The inside windings are very close together. I haven't tried it yet. Soon. I have a problem with my knee stopping me going up in the attic to wire it all up at the moment. Oh, I will add that in order to make the auto transformer, I didn't solder on another lead, after two turns I took the wire out and back again, and twisted it together, before carrying on the winding. The sticking out bit is then a twin twisted wire.
Hi, I'm new to the hobby glad i found your channel and the excellent research that you have done on the best cores for EFHW transformers. I will be definitely making my own 49:1 using the core you suggest and auto transformer winding as it's so straight forward to make. Long story short I will also need a common mode choke to stop the very short run of coax being used as the counterpoise rather than the actual counterpoise, do you have a recommendation of the best core for the choke. Thanks in advance
I would like to see how a 2 to 14 (or 2 to 15) transformer, with no connection between primary and secondary windings, compares with the two variations of autotransformers presented here.
Thanks for interesting information. I understand there are 14 turns with the auto transformer. According to your table. Will you test swr in your next test?
@@MM0OPXFieldRadio I wonder how well this core would preform if designed and assembled based on 64:1 unun ( 3 primary/24 total ). Do you think it would matter Collin?
Thanks Colin. Great videos. Yesterday I built the 56:1 wide wound on the 1002 and I just tested and trimmed the radiator. I'd be so grateful if you would comment on these results because I'm wondering if I should change it to 49:1. I used 1mm enamel wire on the toroid and 18g on the 67' radiator. SWR dipped to lowest at 6.830, 14.050, 21.150 and 28.100. 6.830 got 1.0:1. 7.050 got 1.4:1. 28.100 only dipped to 1.9. What do you think? Thanks, Scott in NC
Antenna orientation, ground effect can have a massive effect on this. They seem to be fine. You wont see super low dips across all bands but as long as its less than 2:1 dont worry, I dont. I found best results as an inverted V with both ends well off the ground. With the transformer close to the grounds it was always worse.
@@MM0OPXFieldRadio Thanks! I have seen two opposing views on deploying the transformer near the ground. I just installed mine about 2' up with a short wire to my grounding system per Steve Ellington N4LQ's videos. I gather you would not do that. If you're willing, tell me your preferred distance and whether you would do the grounding or any kind of a counterpoise. I am using a 67' wire in an inverted L/sloper kind of setup. I could do the inverted vee though. Thanks again, Scott NZ4R
@scottcarter9975 I found the ground effects tuning massively and when you want multiple bands to tie is it can be difficiult. My feed point is at least 4ft off the ground which I find helps. Remember this is a dipole, just fed at the end. Height is always might.
Sorry, I meant to say 1002 cores. I guess my point is what real world numbers are you seeing when attached to a resonant long wire.? I like getting low VSWR on all bands and making the transmitter "happy". I'm wondering if there's a trade off, efficiency vs tune-ability? for lack of a better term. I know your waiting on better weather for this particular configuration, but previous tests? Thanks, John
Your right, there is a trade off and I've said this many times before. Just because its efficient doesn't mean its going to have an acceptable VSWR. For one thing its easier to wind and thats a winner for me if it works on air.
Have made this transformer yesterday end did an activation today. A halfwave lengt for 40m, 40m at the long side 1.18 at 7.180. 20 is good and on 10 had a reel high swr, wire to long… Does make a 15:2 a better match?
I think it is not fair to change the winding ratio from 2:15 to 2:14. This reduces the impedance level at the interconnect. This may change the capacitive loss in the core. I would love to see the results for the same turns ratio. besides this, 90% efficiency is really good for a high impedance device.
If you have seen any of my precious videos you will have seen I have done a 2/14 standard winding. The whole point is seeing what we can get out of this core. As far as improving efficiency above 90% its negligible gains yes but why not try just for the sake of it.
i have build one with that core as autotransformer 49:1 … swr on my most liked band (40m) is 1.7 and 2.0 at the end… i think i Must go to 1:56 or 1:64 … but how good is the effectivity then?
Can you stop experimenting on these bloody things....just when I decide to try one, you improve the bloody thing again......STOP PLEASE...your driving me insane....and it's a VERY short trip.
Just make one. You'll never notice 5% heck You'll likely never notice 20%. Remember you have tou double yer power to gain half an s-unit or see 50% loss to loose half an s-unit...however you want to look at it. Assuming a standard 100w radio and the first design here with a SWR under 2:1 yer gonna get 80 or so watts out. That last 20w(impossible to get 100% of) would at best represent a 25% gain ore 1/8 of an s-unit...not even enough to notice on a small anolog gauge or be represented on a segmented digital one. Your time is far better spent building a moxon you can aim wich would net you 3db over the efhw or the same as doubling yer power and getting that full half s-unit with the bonus of the front to back ratio giving you rear rejection of noise etc. Basically chasing that last few percent on an efhw is a fools errand and the times better spent making a secondary directional antenna to play with. Heck even a simple 1/4 vertical like the DX comander will get you some DX gain over a efhw due to take of angle and ditch toroidal losses. Comercialy costs more but diy doesn't.
I guess my point is, don't miss months an months of the peak of this solar cycle agonizing over getting it perfect when the difference between good enough and theoretically impossibly perfect are virtually impossible to tell in actual practice. Get a wire up and play!
@@MM0OPXFieldRadio ...I'm having a couple muled down from Canada to Mexico soon, gonna order some 120pf TDK caps too... they are appparently useless for 80 (not enuff mu @125), but are champs on 40 and above (credit to the ' Evil Lair'), and when wound 14:2 tapped with an extra turn15:2... should be a good experiment. With 90% to 95% efficiency, I fully believe 100w FT8 and upwards of 250, maybe 300 watts (peak) SSB (35% duty cycle) would be no problema. Unfortunately, 52 material cores in the '002 form factor are not yet avaiable... that would be the perfect mix.
