EFHW emissions violate FCC rules

[@martinnelson-j6u]

The various ferrite "mixes" (or types) have several highly temperature-sensitive characteristics that affect transformer linearity, most their notably permeability change. As perm changes, the magnetization curve (BH curve) tilts introducing transformer harmonic distortion. Core suppliers can provide material characteristic data sheets. I have always believed that HF and up matching transformers use for any antenna are not ideal due to their losses (heating), and best to utilize a matching circuit or ATU instead. Your work reveals something most have not previously considered. Good job.

[@Jimscoolstuff]

In this more recent video I discuss exactly what you are talking about. kzbin.info/www/bejne/o5bZZWeCZr5mq9Usi=1g-BcCHum8DPr5Vj Thanks for your nice comment.

[@BrendaBrown-iy7mj]

I love your clarity of thinking speaking and measurement design and comparison math tables of the data..

[@DonzLockz]

Excellent demo! This is certainly the first time that I have heard about this.

[@Jimscoolstuff]

Thanks for your comment.

[@Bond2025]

It is his misunderstanding, looking for something that is not there. The radio or circuit he has put together is at fault. The spurious emissions need to be measured from the radio directly using a dummy load, then through the box he has made. You will find it is the box he has made that is causing the problem. If the radio is giving spurious emissions it needs sorting out. The antenna only radiates what is put in to it. Every licenced radio amateur knows this.

[@Clark-N1NVK]

Thank you ! I appreciate your work. Now I have to go build that dummy load for my Nano-VNA.

[@Jimscoolstuff]

Thanks for your comment.

[@oobihdahboobeeboppah]

Jim, I think your title is a little misleading. Someone might read it and think that EFHW (or EF random lengths) are inherently problematic. What about dipoles with ferite baluns at the feed point? What of unun's feeding verticals? The title therefore should focus on ferite core heating and not the antenna as a potential problem. Yes, because EF antennas require an unun there could be a resulting harmonic problem, but the problem certainly isn't limited to that antenna. I suspect also the ferite material would affect the data you secured. You didn't specify that information. Type 31 vs type 43 vs type 52 vs type 61 or Txxx-2. Depending on what the material of the core is will undoubtedly affect the heating vs frequency. And 50°C seems an unrealistic starting temperature; it's hardly ambient except in the Sahara Desert and I don't think many of us live there. I used to live in Phoenix and even that's a tad bit high unless we're frying eggs on the streets (urban legend). Your conclusion about cooling seems spot on. I've thought about that quite a bit and think using a ceramic material might be a better heat sink to attach to since the ubiquitous PVC box does nothing here and mounting flush to an aluminum box might have its own issues (although DXE uses aluminum boxes in their transformers). I like your video and wonder if you could make an update to it with the considerations I mentioned? I'll even provide you with whatever cores I have on hand if you want. Glen KE7FD

[@barryrutkin6216]

Core saturation also is really great at causing distortion/spurious signals. It's not directly related to heat.

[@Jimscoolstuff]

please read the very first sentence in the description. The thumbnail it meant to attract attention which it obviously did. The 50 deg C temperature is not an ambient temperature; it is the core temperature after several minutes of operation. The core will reach 50 degrees after just 2 minutes of transmission on 10 M. It is roughly half way between ambient and the critical temperature (70 deg). Thanks for your comment. 73

[@mareksp9tkw908]

@@Jimscoolstuffcould you share some details of the transformer? Core size and number , winding details, etc... Did you measure efficiency? For the test what modulation did you use, FM, CW key down or something else? These details are important in order to understand your test. If you could post the picture of transformer that would be helpful too. I would like to repeat your tests myself and find the way to remedy undesired effects. GL 73 Marek SP9TKW.

[@Jimscoolstuff]

@@mareksp9tkw908 The core is an FT-240-43 made by Amidon. It is the standard 2 turns to 14 turns with the crossover. There is a good view of it at the 59 sec. mark into the video in the description below. The one titled "EFHW antenna power rating". The tests shown were just 50Watt carrier on or off, no modulation. Thanks for your comment. 73

[@richardwesterman5773]

This is apples to oranges obida. The EFHW is using a "transformer balun", which depends in part on magnetic flux to transfer input power to the output. This heats the Toroid. A dipole uses a 1:1 "transmission line balun" which transfers input power to the output through the transmission line; it does not use magnetic flux for the power transfer and does not heat the core like the EFHW transformer does. 73 de DJ0IP

[@christophersaid4410]

Fascinating test and results. Thanks very much for the video.

[@russ_vee_jr4199]

EEY-GADS-ZOOKS BATMAN! WHAT'S A HAM TO DO? Actually, this is very informative info and is well presented. Thank you, Sir. I'm in the process of putting together a second 56:1 transformer for my 40M EFHW ant using a better toroid, and you just threw a Monky Wrench into my soop. ARGGG I mostly operate SSB voice and don't expect to get into this problem there with my 100W 590SG, but I do intend to operate Digi/APRS/WSPR/etc on HF in the near future and also get back into CW and I should deffinatly take your information into account. I'm thinking of two stacked cores with an ALU disk, with cooling fins/tabs, sandwiched between the cores using PC-CPU type heat compound. I'd tie the cores together with TieWraps. Alternately, a single core with a tabbed ALU disk at each end should be sufficient for 100W Digi ops. Maybe, I HOPE. A few each of the 15 turns of enameled wire should fit safely between the fins, I think/I hope. I'd cut the disk out with a Dremmell and bend the fins/tabs in alternate directions, up/down. Yet Another Snot on the Door Knob of Life to Deal With. DRATS. Double DRATS Even...... 73 OM, and thanks for this info.......

[@Jimscoolstuff]

Thanks for your comment. Good luck with your experiments. Remember that heat means losses, so a lot of your RF is wasted making heat.

[@daveN2MXX]

Wow....great work. This is what amateur radio is all about!!! I hope the 100W FT8 folks pay attention.

[@StreakyP]

Thinking about it there may actually be 2 different heating rates.. the one you measured when it is reasonably efficient when it is in the cool linear region, then as it heats up and becomes non-linear and inefficient absorbing more and more power so heating up faster as it hits thermal runaway

[@fredmeier3515]

Is it the Ferrite that is at fault, or is it the transformation? Would an aircore linked transformer be a better choice?

[@MattHeere]

Part 97 specifically indicates that these measurements are to be taken at the output of the final power amplification stage. This is interesting, and in the spirit of good amateur practice it's worth continuing to look into. However it's a stretch at best to claim the emissions from an EFHW are "Illegal". So long as what comes out of the finals is legal it appears to me that you're 100% compliant with the regs. Take the reverse situation: are the import HTs that clearly generate excess emissions OK because their antennas are terrible and don't radiate those emissions? Of course not. This is why it's measured where it is.

[@briansauk6837]

You are spot on. 97.307 (e) is very clear - input to the antenna transmission line. I do appreciate his efforts, but definitely bogus to call it illegal.

[@JxH]

By that logic, back-to-back diodes installed at the antenna (designed to square-up the RF, generating endless odd harmonics) would not be illegal. Right ? Hmmm. Perhaps there are other regulations in existence than just 97.307 (e) ?

[@richardwesterman5773]

This may be legally true, Matt, but that won't help you much if you get a pink slip from the FCC.

[@moozoowizard]

​@@JxH this

[@richardwesterman5773]

Excellent. Good to know, especially that it occurs long before SWR creep begins. May not be a problem with SSB but certainly with digi-modes!

[@Bond2025]

SWR creeping up usually happens with poor quality ferrite rings. They DO heat up when you subject them to RF. If you use something too small, or use wire that is too thin, it will all heat up. Use something that is not just rated for your maximum power, but overrated by a few times.

[@buildstoys]

Jim, I'm not seeing those Ohmite in the TCH series on Mouser -- could you provide the part number you used?

[@Jimscoolstuff]

I guess I got my projects mixed up. The resistors that I used in the dummy load was a Caddock part. The Mouser part number is 684-MP9100-50. Sorry for the mix up.

[@fotografm]

I really enjoy your solid engineering approach to ham radio topics. Were you a NASA engineer in the past ?

[@storskegg]

So, just some things I got curious about while watching the video...the time to cool of 1.88C/min...is that average? Is it linear, or is there a curve? Re: the temperature increases per band, I'm interested in seeing how that matches up to the core's position on those ferrite core efficacy spreadsheets out there...the ones where green and a black line are good... (sorry, spacing). Also, do you have a part num for the Core-under-test, and what's the placement of the thermistor? I might try this with the thermal scope. Excellent video.

[@Jimscoolstuff]

The cooling rate is a function of the core temperature above ambient temperature. The core that was used is an Amidon FT-240-43. Here is a link to another video on the subject. kzbin.info/www/bejne/o5bZZWeCZr5mq9Usi=UEX0SrO7rIjK9y14 I am working on a second part of that video.

[@StreakyP]

Fascinating work thank you. It would also be interesting to conduct these tests on some of the "snake oil" commercial multi band verticals that have the heat-sinked baked bean can full of ferrites a the base.

[@gordslater]

great work there - many thanks for taking the time

[@Jimscoolstuff]

Thank you for your comment.

[@koldark]

There are plans out there to add a fan to the box to keep the core cooler. But is pretty interesting test.

[@Jimscoolstuff]

Thanks for your comment.

[@JxH]

NEWS FLASH: Ferrite has been used in the feed of many types of antennas, it's not just an EFHW thing. Baluns were a 'Very Big Thing' in the 1970s. Also, EFHW, being extremely high-Z, would have less current and thus less core saturation than other antenna types.

[@Jimscoolstuff]

First of all, the cores are fed at an impedance of about 50 ohms thru the two primary turns. This means that the full output current of your transmitter is applied to the core. Second, the problem does not appear until the core reaches a critical temperature, so depending on how you operate, you may not see the problem. Third, the folks selling this stuff don't want you to hear of this problem. For a full understanding of the issue please watch these two videos. "EFHW antenna power rating" and "EFHW spurious emissions caused by ferrite toroids" Thanks for your comment. 73

[@richardwesterman5773]

Not all baluns were created equal. Transformer Baluns tend to heat (or even overheat) whereas Transmission Line Baluns do not; at least not nearly as early. Dipoles use Transmission Line Baluns whereas EFHWs use Transformer Baluns . It is indeed a potential EFHW problem.

[@tomsherwood4650]

SO would like to see other ways to feed the EFHW that do not involve a ferrite transformer, even though I would assume these methods might only work on a single band at a time and require tuning.

[@steve1x3x]

Could one use an air-core autotransformer with more turns >> equivalent inductance to ferrite core device? would there be too much capacitance between turns.>self resonance?

[@dennyoconnor8680]

A parallel tuned tank circuit with an air variable and a coil is the gold standard.

[@GoonyMclinux]

​@@steve1x3xlook at an imax 2000 match.

[@richardwesterman5773]

There are already two good replies. The original circuit for matching this was patented by Josef Fuch, an Austrian amateur about 100 years ago. The ARRL published his design in the July 1928 issue of QST. He used a link-coupled tank circuit with air-core coils, AND a capacitor in parallel with each of the two coils. However, in practice, most just had a variable capacitor (or trimmer) on the antenna side of the tank circuit. This was a very popular antenna for many years, long before we had Toroids. Most of the documentation is in German and now days show builds with Toroids, however here is one that shows a table for a few bands and specifies how many uH the coils must have: www.baeckerei-heitmann.de/DF1BT/Fuchsantenne_30M_DF1BT.pdf You can use this design but with air-core coils.

[@Steve-GM0HUU]

Thanks for sharing this Jim. It would certainly be good for others to repeat this test to see if similar results are obtained. Of course, as you say, ARRL (or someone with proper lab environment) looking at this would be good. In addition to EFHW UNUNs, wondering how this might affect use of toroids in multitude of applications - PA stages, antenna matching circuits, filters, etc? Basically, any application where toroid cores are being used and subject to significant heating.

[@Jimscoolstuff]

Thank you for your comment. I would like someone to confirm my experiments or even confirm that the cores get hot. In other applications there should not be any problem unless the cores get hot.

[@subramanianr7206]

Ferrite cores do get hot sometimes to the extent that they get shattered in high power applications. Many have complained of the heating up of EFHWA UnUns with high power and many solutions have been suggested. In high power, solid-state power amplifier ferritr loaded output transformer designs harmonics are anticipated; so, low pass/harmonic filters become mandatory. This is the first time I have seen one is experimenting to look for harmonics in the efhwa UnUn transformer. Thanks for your efforts 👌 De VU2RZA

[@jluke6861]

What a great Channel. Thank you.

[@Jimscoolstuff]

Thanks for your nice comment.

[@hepcat67]

What core material did you use?

[@Jimscoolstuff]

I used 43 mix ferrite cores.

[@azav8raa]

Nicely done, Jim. I really enjoyed your scientific approach to the analysis and the conclusions. The ARRL labs should get their priorities figured out and move this higher on their list. Especially considering the popularity of the EFHW and high duty cycle modes like FT8, ETC… de KB7ZUT

[@skepticwest9628]

The ARRL is selling single core EFHW kits for $79 as a fund raiser.

[@subramanianr7206]

So, naturally, they may not be interested 😅 De VU2RZA

[@BusDriverRFI]

Believe me. They don't want this looked at.

[@rickbattle5706]

There is one large question. Did you apply a constant signal to the transformer? IE key down CW or FM? That will heat up the toroids for sure, but is that what happens in the real world? No, certainly not. The duty cycle of an average CW signal is way below 100% and no one runs FM on 40m. Therefore, the toroids would experience one 50% cooing cycle for each 50% heating cycle. I think if you apply real world applications and real world uses by everyday hams the results would be very different.

[@Jimscoolstuff]

I usually run FT8 which transmits PSK for 13 seconds, is idle for 2 seconds, and listens for 15 seconds continuously. That is a 43% duty cycle. When the core heats up faster than it cools down, the core temperature will steadily increase over time. You are correct, CW and SSB are much lower duty cycles. Thanks for your comment.

[@tomsherwood4650]

How long to heat up if used at say 100W PEP SSB with the typical duty cycle of a ham QSO, with nothing like a constant signal. Talk for 30 seconds and off for a minute. It is good to know this issue but makes me think of things such as tube ratings, like how they rated tubes for intermittent ham radio apps versus the lower power ratings for continious output like broadcast.

[@Jimscoolstuff]

Be sure to watch the video on power rating. there is a link in the description. In that video I compare the duty cycle of SSB, CW, and data. thanks for your comment.

[@snakezdewiggle6084]

Good job Jim, thank you sir.

[@Jimscoolstuff]

Thanks for your comment.

[@Aimsport-video]

Not specific to EFHW… Thermally induced core harmonics don’t care what wire topology comes after it.

[@Jimscoolstuff]

You are correct, but I don't know of any other type of antenna being fed from a ferrite core. Ferrites used as chokes do not even get warm. Thanks for your comment.

[@n0vty873]

I do not show these emissions from my efhw, mine must be broken.

[@ssnerd583]

It would seem that a small 5v fan from an old computer could be used to help cool the cores

[@tomsherwood4650]

Usually the cores are well away from any convenient location that a fan would be practical, like someplace high up outdoors.

[@ssnerd583]

@@tomsherwood4650 ...how about a Peltier cooler on a thermo switch

[@ik04]

I have considered mounting the toroids in a finned metal box filled with oil to dissipate the heat. Has anyone successfully done that?

[@Jimscoolstuff]

Thanks for your comment. Several people have made the same suggestion, but I don't know of anyone actually doing it. Good luck.

[@ploegmma]

Well done! And thank you 🙏

[@Jimscoolstuff]

Thanks for your comment.

[@birddog1148]

Can you try it with multiple cores?

[@Jimscoolstuff]

Hopefully others will work on this problem. I have other projects that I want to work on now.

[@BusDriverRFI]

This is probably going on with most all toroids. These are very lossy devices and cause excessive harmonics. The ARRL wants to sweep this under the rug since they make so much money derived from these products. Yet we have many KZbinrs touting their harmonic generating toroidal devices while slamming other devices that have too many harmonics. It's a rip-off industry.

[@Jimscoolstuff]

The problems occur when the ferrites get hot. The temperature depends a lot on your operating methods. Casual contacts or contesting is very different. Thanks for your comment.

[@BusDriverRFI]

@@Jimscoolstuff this is true with your experiment. The reason the toroid increases harmonics is that there's too little permeability for the RF peaks and they clip. With your mix, there's enough at first but the heat decreased the permeability. Hams lose a lot of power in these toroids. Otherwise they wouldn't heat up at all. The correct solution is to find other solutions. The efficiency is very low. Can you tell me what the unloaded input XL is on the transformer? Disconnect the output from the transformer and measure the inductive reactance of the input turns is how you can measure that.

[@75ohmHAM]

New Hams, Pro Tip; whenever another ham uses the word 'illegal, walk away.

[@Jimscoolstuff]

Is it illegal to transmit in an amateur band without a license? Is it illegal for a licensed amateur to transmit outside of an amateur band. When harmonics that are generated by faulty equipment fall outside of amateur bands, is this illegal?

[@AE5X]

Power levels are measured in dBm, not dB. You are incorrectly expressing them both in dB. It matters and might be confusing to newbies who want to learn the correct nomenclature.

[@Jimscoolstuff]

You are correct when talking about absolute power. When comparing ratios of power (relative power) dBm is not used.

[@AE5X]

@Jimscoolstuff i refer you to what's written on your chart early in the video.

[@Jimscoolstuff]

Sorry, but I can not figure out what you are referring to. Please tell me the time in the video where you see the problem.@@AE5X

[@AE5X]

@@Jimscoolstuff 09:35

[@Jimscoolstuff]

Technically you are correct about the measurement of the magnitude of the fundamental. In talking about the magnitude of the harmonics I am speaking about them relative to the fundamental "dB down". Thanks for your comment and best regards.@@AE5X

[@jonathancotner7040]

If your cores aren't rated for the power you're using, then yes they'll heat up. The fact that they're heating up tells me you're not using the right core, or you're exceeding the power rating for the core.

[@Jimscoolstuff]

Please tell me the power rating of the FT-240-43 core. Thanks for your comment.

[@DanielHallmark]

​@Jimscoolstuff Check out the videos put out by MM0OPX on the impact of various core mixes and designs at different frequencies. He is looking specifically at efficiency and loss in the cores with different windings, stacking, etc. In particular, 10m has really low efficiency as you have observed.

[@evertwenderpirt6328]

very good!!

[@Jimscoolstuff]

Thank you for your comment. 73

[@johnarcher9480]

So, starting at over 120 degrees and keying up on FM for a minute heats the cores enough for spurious emissions? Ok, what if we start at 60 degrees? Also, the FCC rule is measure that the transmitter. You are breaking no rule with the EFHW even at over 150 degrees. This seems rather misleading.

[@Jimscoolstuff]

I show the rate of temperature rise in the video. It does not matter where you start. Ask yourself; what is the intent of the FCC rule? Is it bad when a transmitter causes interference, but OK when an antenna matching device generates interference? Was the FCC rule written before non-linear devices were being used in this way. If someone hears your out-of-band signal does how it was caused really matter?

[@johnarcher9480]

@@Jimscoolstuff EFHW antennas aren’t really new. Yes, the rate matters. Versions are made for different power levels. They stay cooler under power. Getting to the Currie point is not something you want to do. Getting a transformer that suits your station is the important part. A working transformer doesn’t put out spurious emissions…as you showed. Abusing a transformer isn’t the goal of people who use these antennas. Whether it’s the spirit of the law isn’t really relevant. The rule is the rule as written. That said, EFHW antennas are not putting out “illegal” spurious emissions. That is simply click bait.

[@Jimscoolstuff]

Please look at the FCC definitions of "antenna" and "transmitter". An antenna is a device that converts RF from a transmitter to radiated energy. This means that the ferrites are part of the transmitter. A transmitter is a device that delivers RF energy to an antenna. As with all legal definitions they may be subject to interpretation by an individual. @@johnarcher9480

[@johnarcher9480]

@@Jimscoolstuff I think it would be a stretch to call a transformer a part of the transmitter instead of part of the antenna. By that definition, any SWR meter or tuner would now be transmitters. As would any coax in the system. And again, when you tested it, it showed NO spurious emissions. Only when the ferrites were abused, did you start to see some spurious emissions.

[@Jimscoolstuff]

SWR meters and tuners are often built into transmitters. Are they then part of the transmitter? The same for a power amplifier. Is the output from a power amplifier exempt from the emission rules? We could go on and on like this. I think that we should agree to disagree and stay friends. 73 Jim KQ8E@@johnarcher9480

[@paulwyleciol3459]

cool! 😅

[@Jimscoolstuff]

Thanks for your comment.

[@Bond2025]

This video is absolute nonsense. Do the following - Measure the spurious emissions from the radio going in to a proper 50ohm dummy load Measure the spurious emissions from a signal generator to a proper 50ohm dummy load for comparison. Connect up a EFHW antenna to the radio directly and test SWR. Use the nanoVNA to look at spurious emissions using a small antenna so as not to overload it. Connect a RF signal generator to the EFHW and repeat measurement of spurious emissions. The transformer you are using and/or the wire are TOO SMALL, you need to use better quality and bigger ones to handle continuous not just bursts of peak power. The antenna *ONLY* radiates the RF put in, so if you have a radio giving off spurious emissions you will see problems. The antenna *DOES NOT CREATE* spurious emissions all by itself, which is what you see to be incorrectly suggesting. You appear to have a complete lack of knowledge of RF, how to construct RF circuits, antennas, radio and test equipment from the demonstration you give. The false results you are seeing are caused by the circuit YOU have put inline, nothing else.

[@Jimscoolstuff]

Thanks for your comment.