I can’t find an actual online calculator that will come up with the numbers. He does the math and shows screenshots of calculations but I can’t find where he provides an actual online calculator.
One pointer I can take away from Duffy’s site is that a single FT82-43 core may be insufficent to handle 12W cw from my KX2. He states that “max continuous average power” for a single FT82-43 EFHW xfmr in free air is 2.7W, but not exactly sure how to translate that for cw and xfmr in an enclosure but it would seem to be dangerously low for running 12W cw.
A loss of 1.5db has no noticeable effect on the efficiency of the antenna. Most qrp antenna tuners suffer similar losses, especially at random long wires.
It should be indifferent in most cases, whether you heard with S5 or S4 3/4.
The decisive advantage for me, especially for Sota, is that I’m qrv without tuning and without changing over on several bands with a feeding point near by the ground.
I just made a test with a HAM about 5 km from my home.
On 40 m the endfed with the 43 material transformer was 1 S-unit less at the receiving station than with the material 61 transformer! On 20m there was no difference in signal strengh although the power measurement results yesterday showed a higher loss on 20 m.
Endfed with 61 material transformer showed the same S-meter reading compared to my linked dipol.
The performance of my transformer construction is ok from 7 MHz to 14 MHz. Currently I only have FT 114-61 available but for 10 W it should be ok. I am using 3:27 turns and 330 pf…
My endfed is a trap-version for 7/10/14 MHz, halfwave length on each band, no harmonic operation.
Results for me: for the moment I will carry my 61 material modified endfed along for my upcoming activations.
Tanks for the links, there is a lot to read and still a lot to learn about.
The QRP EFHW xfmr that Owen Duffy recommends is wound on a round cable core (type 43), not a toroid. A crucial parameter for power handling is a parameter related to cross sectional area and path length and this is superior for the cable core versus the toroid. This is the core he used in his recommended xfmr. I suspect it might be challenging winding many turns on it.
yes, thanks for you comments. EFHW is very good antenna for SOTA, I use it myself also.
What I wanted to know is that has some one measured these transformers and now I can see they have. Thanks for their efforts.
quote “Just wondering if anyone else has measured these famous efhw transformers with diffirent core materials? Oh yes, I know it is only one dB, but thats not the point here.”
Your conclusion regarding the efficiency of the ferrite mixes 43 and 61 seems to me a bit daring and too generalized (not taking into account the frequency range of operation). The main reason is because not both of the compared Ununs have an optimal design which can falsify the results.
It would be interesting to see if/how the core efficiency (along Owen Duffy) plays in your comparision using a rewound FT-140-43 3t primary and 21t secondary?
Note: The value of the compensation capacitor may need to be adjusted.
Here are efficiency figures for 14MHz per Owen Duffy calculation method for type 43 ferrite and 3T primary. First figure is for single core and second figure is for stacked dual cores:
That is what I measured yesterday. At 14 MHz FT 140-43 (2 T primary) single core loss 1.75 W, that results in an efficiency of about 83 % or am I wrong?
Ferrite materials can vary considerably depending on the manufacturer and even the batch. Tolerance for AL is typically +/- 20% so it’s possible that this is just a particularly efficient core. The core could be anywhere from ~60% to ~74% efficient with 2 primary turns and still be within tolerance.
Peter, if you’d like a better idea of what the AL of that core is you can do a quick test by putting a bunch of turns (Fair Rite uses 5) through the toroid, measure the inductance in uH, then do a bit of algebra and work out the final value: uH=(AL*Turns^2)/1000.
As a not so well qualified layman, it is not so clear to me what is being implied here. Are we talking about insertion loss or blocking impedance, or neither? Doesn’t the importance of one over the other depend on what kind of antenna you are building!
Cheers Matt
I believe the efficiency numbers are losses incurred in the transformer material. Another consideration is SWR losses introduced by too low inductive reactance of the primary winding (which is effectively in parallel with the transformed impedance of the antenna, which should be 50 ohms by design). A primary inductive reactance of 100 ohms results in an SWR of 1.5:1 if the antenna is optimally matched. So you really want at least 100 ohms and hopefully a bit more. This is what makes type 61 ferrite a challenge - for the primary winding you need 4T@14MHz and 5T@7MHz to get this much due to its lower permeability. 3T with type 43 gives far more than 100 ohms (i.e., 200-400 ohms at these freqs) so it’s easy to get low SWR and reasonable number of windings.
