EFHW power rating myths

You can determine the power rating for yourself. Don't rely on myths and exaggerations.
Watch these videos to fully understand this problem.
This video gives you background information on power rating.
• EFHW Antenna Power Rating
This video explains how the non-linearity of ferrites generate illegal spurious emissions.
• EFHW Spurious Emission...
This video shows how to measure illegal harmonics with a spectrum analyzer.
• EFHW emissions violate...
This video explains how thermocouples work.
• Thermocouples, how the...
This video demonstrates a low cost thermocouple meter and demonstrates why infra red (IR) temperature measurement depends on the emissivity of the object.
• Thermocouple Meter Rev...
Here is a link to part 2 of this video:
• EFHW Power Rating Myth...

[@norbertstepien9185]

excellent video. As a builder I was concerned about the unanswered questions that you address in your video. Thank you.

[@Jimscoolstuff]

Thank you for your comment.

[@xtogarcia1463]

Muy interesante.Este tipo de experimentos explican muchas paradojas y mitos extraños de la radioafición. Gracias por su tiempo, compartir e interés.

[@neilbchilton]

Thanks Jim, this is really useful information. I think you're the only person covering it in this level of detail. I'm looking forward to the next video where we see the actual temperature increase in the ferrite... and dummy load I guess. I've often thought it strange that none of the commercial transformer designs consider cooling or passive heat transfer. I only use QRP right now , but still very interesting! 73s

[@Jimscoolstuff]

Thanks for your comment. 73

[@mareksp9tkw908]

Thank you Jim for detailed explanation and crush reminder course is basic thermo-physics. Looking forward to part 2.

[@Jimscoolstuff]

Thanks for your comment.

[@jbammi]

Thanks Jim, Very interesting topic like most of your videos and really marvel at the innovations you come up for the jigs for the metrics you are trying to measure. Curious about one thing: When you measured the ferrite code temperatures you ran the rig key down 100% duty cycle. Wouldn't a more realistic model use the duty cycle of say a digital mode - FT8 15s on / 15s off, or for FT4 shorter on/off cycles? Also, as you point out most transformers come in a enclosed box for weather/dust protection, or the QRP ones shrink wrapped around some sort of support like a winder (yes there are some unprotected ones wire wrap tied to a support. Keep them coming and we'll keep on learning. Thanks again 73 de k1jbd, bammi

[@Jimscoolstuff]

In part 2 of this video ua-cam.com/video/I1ePw6PQ0io/v-deo.htmlsi=lN4rnKtSCqU7Hxg-
I use FT8 to show temperature rise and the SWR heading toward infinity. Thank you for your comment

[@revbikerbigd8664]

Thx Jim, eye opening !

[@Jimscoolstuff]

Thanks for your comment.

[@yannkitson116]

Very interesting, thanks for sharing.

[@Jimscoolstuff]

Thanks for your comment.

[@youtubeaccount931]

Great experiment.

[@Jimscoolstuff]

Thanks for your comment.

[@oobihdahboobeeboppah]

Thank you, thank you, thank you!

[@Jimscoolstuff]

Thanks for your comment.

[@subramanianr7206]

You are a good teacher and experimenter. Thank you.
VU2RZA

[@Jimscoolstuff]

Thank you for your nice comment. 73, KQ8E

[@terryandersonart9007]

Good info video Jim!

[@Jimscoolstuff]

Hi Terry, thanks for your comment.

[@PeteCorp-zd1ih]

Great info. Thank you so much Jim.
Pete, wa2jmg

[@Jimscoolstuff]

Thanks for your comment. 73

[@mikesmith5139]

Hi Jim, Thank you for your extensive experimentation, testing and analysis. I really like the EFHW antenna idea as it can work several / multiple bands, it avoids the potental ground losses of a ground mounted 1/4 wave vertical antenna / Marconi antenna, it is stealthy, easy to install with minimal visual impact, and when a EFHW is installed at an Inverted L or vertical it gets the current point high in the air. I like all these things, but I have always suspected that too much power (20 to 30%) is lost in core heating. I therefore use 2 stacked FT-240-43 cores as an absolute minimum for 100 watts SSB, and would never use more than 20 watts for digital modes. But my question is this: Jim, is there there a better method - avoiding the use of ferrite ununs - to feed a 20 metre long End Fed Half Wave antenna wire for operation on 40m / 20m / 15m / 10m ?? Thanks, Mike, M0MTJ

[@Jimscoolstuff]

I also like the EFHW antenna. The losses in the ferrite core are no problem from a communications standpoint. When the cores get hot they generate illegal harmonic radiation. When they get even hotter, your SWR will increase and you may not notice it. The problem gets worse when the UNUN is sealed inside a box or covered with shrink wrap. Most amateurs listen much more of the time than they spend transmitting so the cores have time to cool.
I don't know of a way to make a 49:1 UNUN without using ferrite cores. The commercially made units are over hyped from a power standpoint and sealed up in a box so you can't feel the core temperature. They also mention nothing about core temperature and harmonic radiation.
Thanks for your comment. 73, Jim, KQ8E

[@mikesmith5139]

​@@Jimscoolstuff Hi Jim, Thank you for your follow up - Much appreciated and very helpful. 73, Mike, M0MTJ

[@thedabbler2753]

Thank you, Jim :)

[@Jimscoolstuff]

Thanks for your comment.