End Fed Half Wave Effieciency - Resistor vs Back to Back Methods
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- Опубліковано 22 сер 2024
- In this video I show comparisons in EFHW efficiency testing methods - Back to Back vs Resistor.
Link to my results spreadsheet, feel fee to download a copy
docs.google.co...
Link to a couple of Owen Duffy Blogs
owenduffy.net/...
owenduffy.net/...
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The value of that test resistor has always fascinated me. I had an idea the other day, and tried out measuring the antenna side of the transformer with my 50 ohm cal std on the "radio" side. The values were close to 2400, but varied a lot over the frequency range. 2.5K ohms at 4Mhz, 2K at 20Mhz, 3.3K at 30Mhz. I even used the S21 serial R measurement method for high values of resistance...
As a cross-check for my procedure, I measured a carbon film, 2415 ohm (Agilent 34401A) resistor, and on the Nano it ranged from 2.1 to 2.6Kohms. My method for measuring loss is much, much more primitive than yours. I have about 5 various transformers, and I use one as a "standard" and measured the other 4 against it, took an average of 1/2 of the loss readings, and use that value as the amount for the "standard"... All are various 49:1 z windings, tapped, twisted, cross-over, tight, loose etc. I am within about .5 to 1 db of your values... I'll have to try the two of the same type back to back one day.
I also own a DG8 VNWA, which has a super software package that includes math "expressions" that you can plot. Saves you from having to cut and paste readings into spreadsheets, you just plot the formula (expressions) with the live s11 and s21 sweeps within the formula... Its also within .5 to 1 db of your readings.. Interesting stuff, thanks for your work, and attention to detail... 73s
Thanks for sharing your insights. Its incredible to think my little 2015 vintage NanoVNA is as good as it is. I need to get a newer ones with a bigger screen and N type connectors. When I SWR sweep with a resistor the response is far from linear as you note here.
bear in mind that the 49:1 ratio is only a nominal ratio, and assumes perfect transformer action. the number of primary windings determines how much primary inductance you have and how well the transformer works as a transformer on the low bands. the leakage inductance of the transformer determines how well it works on the high bands, and the compensation capacitor is there to match this leakage inductance to keep primary impedance looking OK for the transmitter. So it's not surprising that the output impedance will vary. All it means in practice is the tuning points of the high bands move around a tiny bit.
These are amazing results but for another reason... You know how when you wind toroids for filter you can't rely on 2 inductances being identical & often have to tweak the winding spacing slightly to finally align the filter (to account for variations in the material mix & winding capacitances).. with your single unit and double unit results being sub1% correlated it shows how well/accurate/repeatable you have built them AND that the core manufacturer's material chefs are getting better at cooking up more consistent mixes of ferrite.
Great video... Very helpful.. many thanks
Fantastic alternative view. Your right, takes a lot of variables to line up for this little variation.
Thanks Colin, looks like which ever one you like to do is the best method. Like you said not much difference.
Exactly, just give additional assurance. Looking forward to your next Hexbeam video!
Great work. Even if the absolute results differ between the two methods, the relative results for either method should be consistent. In other words the simpler method would still allow you to select the most efficient core and winding method for your needs. Y
That's how I see it. I wont muddy the waters.
Again excellent video Colin. I think the difference on the higher bands is relating to the length of connections. If you look back at your older videos you will notice that some of you leads on antenna end are 4-5cm long at least. I am building now a measurement rig with SMA connectors and plan to use that for tests. You can see effect by first measuring transformer with antenna end about 5-7cm and then shortening it to just 1-2cm. Of course once in the box that doesn't matter as this connection becomes part of the antenna. You wonder why I want precise efficiency? Well it is to establish maximum power handling for that transformer. Again Owen Duffy has calculator to establish amount of losses (W) which will increase temperature of the core by set amount. This value can be used to calculate power rating by band and modulation. As more and more people are using FT8/4 at higher power level, this issue becomes important.
GL 73 Marek.
PS thanks for a mention.
Super thanks Marek, I couldn't have done it without your help. Its a fascinating subject when you get into it.
Awesome! as always, well explained. Thanks for taking the time to print out the chart!
Oh and don't forget about the car (HAHA)
Thanks and Yes, better off to forget about the car, it needs a new exhaust piece but unfortunately it has both the DPF and CAT on it :(
Back to back is the best method when you check non-50Ohm circuits and you have a pair of devices to test. Any component added puts its own parasitic parameters into the circuit. Marek’s solution is good if nothing else left.
@PawelSamoHa the biggest problem with back to back is to have two identical units. Because toroids have +/-20% tolerance in AL value you would need first pick up two with the same parameters. Method shown by Colin does not have that problem.
Great vid Colin - thanks 👍🏻
Thanks Mike. Weathers getting better for getting out portable.
Good morning, Colin. Excelent. 😀👍
Good morning, thank you 😊
Thanks for sharing the resistor method. I started a build with the intention of doing back to back but haven't progressed past the first autotransformer yet. Stuck there for being laz^H^H^Hbusy. Guess It'll get going again. 73
Plenty of time to get to it. As long as your having fun.
Thanks for the Video. I think the resistor method can safe some time while exploring new designs/cores as only one transformer have to be build. That was the reason for me to investigate in it (yes , I'm lazy 😂)
As the load resistor is not linear over the frequency range, there is a little measurement error by using the "theoretical loss". Better to sweep the resistor with a vna and use this as correction. Also, I think your external resistor should only be 2400 Ohm, as the S21 port of your Vna will add its internal resistance of 50 Ohms to the chain. But also here the measurement error will be rather small due to the high transformation ratio.
73 de DG1JAN
Thanks Jan, I did wonder. I read Duffys blog and it made me wonder and was still an open point for me. I should recheck with just the 2K4 and see the difference. Keep up your work!
When I put two 49:1 transformers back to back and terminate with a 50ohm load I observe the SWR reading on the S11 channel on the nanovna. Now move the termination from the 50ohm load to the S21 post and the SWR changes on S11 port. My conclusion is that the S21 port of my nanaovna is not 50 ohms.
Given all the variables that we cannot quiet pin down and that ferrites are not particularly linear in the first instance ie results at nanovna power levels may not translate directly at 100 watts, I am beginning to think attaching the transformer in an insulated box to a "real world" test EFHW antenna and monitoring temperature rise in response to typical transceiver power output in a valid test and transformer selection method. Impossible to standardise though 🙂. In the past I have also used in- situ radiated field strength measurements to select the best of competing matching networks for a particular antenna. 73 Denis
Thanks Colin I made a new toroid wound auto transformer style and used the same cut length of wire from my first built antenna. It gave me a better Xs value of zero and Rs values very close to 50 ohms with in the bands I wanted. Been working JA ZL U.S on 10m SOTA lately with good coverage on other bands too KX3 @ 8w. Regards good work 73 vk5cz ..
Nice job!, when it works no reason to change.
Excellent work Colin. Tnx for sharing
73 from sweden
/Lars SM3TEK
Your welcome Lars 🙏
really great insight Colin!
Thanks John. The Hexbeam is almost completely finished, I need to upload the latest BOM to my google drive.
Well done Colin! I’ve been able to match your tests in the back to back method. I’ve embraced the auto transformer method of winding a toroid. Much better results. I’ve been testing the FT 2661102002 and for a lighter 100 watt antenna it’s looking pretty good.
Excellent, so many have suggested that core, I need to buy some on my next Digikey/Mouser order.
Resistors are not pure resistive elements. At higher frequecies, the effective resistance will change due to impedance changes. The curves are different for each type of resistor. You mgiht try a small PCB with surface mount resistors.
Yep, not my field of expertise . Jan suggested sweeping the resistor on its own to correct for this. A special small PCB Jig with surface mount resistor as you suggest.
I did a little more searching; if you use a metal film type axial resistor, you'll be good up to 100MHz, apparently.
That's some work!
Thanks TO!
Hi Colin, great work, as always! Interesting method of efficiency measuring. I see that the measures of the 3x stacked FT240-52 with autotransformer are not anymore on the spreadsheet. Why is that? Do you still believe that it's one of the best combinations for EFHW transformers? Thanks!
Great spot. Thanks for the heads up it was missing. Thats my poor version control. I have updated locally with that included. I will upload to google drive tonight or tomorrow.
@@MM0OPXFieldRadio Great, thank you for all your experiments and for taking the time to edit them in videos. Keep up the good work!
Interesting results, of course for much of the time a small drop in efficiency will not represent much at the antenna but a lot of excess heat at the transformer. 73
100%, of course more is always better ;P Bit like turning up to 11!
My descendants left Scotland for the new country in 1690 (Burnett castle or Crathes Castle). Anyway here we are brother reunited through HAM radio! This is excellent work, I have been using the same method and doing my own research as well. You have saved me a lot of time. One question, you mentioned stacking the toroids is the new thing to do. Is that due to the ability to push more power and not necessarily loss or both? Thanks again! '73
Ham radio is great for connecting again as you say! So so running stacked cores does allow you to run more power but because you change the geometry of the cores (as its seen as one piece) you change the efficiency too. On the 1002 core it improves the low frequencies but the higher ones fall off a cliff. The 240 cores stack well however.
Hello, and that you for all your video also for the time you take to share your work.
I have a question I build an end fed using the new toroid and the winding method you use. My problem is that I have a good vswr on 40 and 20 but on 10 meters it at 5:2 very high on 10 meters. Any suggestions that would help bring 10 meters lower on loss
NanoVNA-H and H4 can have an error in s21 logmag measurements of up to 1.7dB. The s21 error increases when the SWR on s11 increases. An efficiency of 99.4% is unrealistic. Perhaps there was a high SWR in this band, hence the measurement error increased and as a result such a unrealistic result.
I agree its unrealistic. As Jan suggested, sweep the resistor as its response wont be the same across the frequency range then adjust for that.
@@MM0OPXFieldRadio In the latest beta firmware for H and H4 1.2.33, the enhanced response function was added, which corrects the measurement error I mentioned. More on this topic on the owenduffy blog in the article titled "An experiment with NanoVNA and series through impedance measurement… a fix"
It doesn't take long to look at Owen Duffy's notes to see he's clueless about antennas.
It makes zero difference . I will continue to do back to back testing. Thanks for sharing !
Agreed, keep doing what you have always done and keep the continuity and relativity whatever method you have started with.
Why would anyone want write access 😂
No idea 🤦♂️, had quite a few requests for it.
Because they don't know how to use a computer and they think the document should be editable by them.
...
I think there's a way to save a Google document so that you can play with it, but it's not saveable. Just don't recall how to do it.
@@jamess1787save to drive, save as something different then you can edit it. It's best to save as something else because if they don't know how to do this they will most likely balls the original up and then forget they had done this, then moan at the author that it's wrong.
@@ifell3 💯 couldn't have said it better myself!
Surround your functions with single ticks ' and that'll allow it to not compute the function. Don't ask me know I know 🤐
Excel is not my speciality, I know enough to get by.
@@MM0OPXFieldRadio you aren't alone. You do an awesome job, just wanted to give you a tip 🙂.
Excellent presentation! DE WA1KLI
Thanks John.