EFHW Spurious Emissions Caused by Ferrite Toroids
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- Опубліковано 15 жов 2024
- In this video we explore the possibility that the non-linearity of ferrite cores that are used to construct EFHW antennas are causing harmonic out of band emissions. These emissions my violate FCC rules and regulations.
Here is a link to my video about the power rating of EFHW antennas.
• EFHW Antenna Power Rating
Here is a link to my video about transformers.
• Transformer Secrets
Here is a link to my videos about Inductors and magnetism.
• Inductors and Capacito...
• Inductors and Capacito...
• Inductors and Capacito...
• Magnets, Electromagnet...
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Brilliant explanation, I never understood how the magnetic hysteresis affected transmission
Thank you for your comment.
Thanks for sharing this good insight Jim. Have nice upcoming week. /br, from Norway
Thank You For your comment.
Nice catch! Looking forward to arrl's response.
Very interesting and very concerning. I'd like to learn more.👍🤠
I have a second video on this subject. Thanks for your comment.
Fascinating, and you explain it so understandably, will look out your other videos, thankyou
Thanks for your comment.
I found those SDR dongles to be pretty good at acting as spectrum analyzers (and dirt cheap, and now with much higher bandwidth & better SNR -> RTL-SDRv4) and better still, SDR# and other programs allow you do do everything from saving "waterfalls", to making a pretty nice scanner, to decoding air traffic transponder signals, weather satellite data, and more (even SSTV with the right plug ins).
I found a ton of harmonics in the AM band from an LED bulb (a cheap Walmart generic one) that I'm surprised is even allowed to be sold.
Thanks for sharing this information.
I'm not a radio guy, but I'd like to be. Subscribed.
Hi Jim, very interesting question/topic. There are often so many other non linear devices nearby that care must be taken when trying to evaluate the harmonics radiated directly by the antenna system versus by other nearby non linear devices but with care you should be able to do a pretty decent job, and looks like you have more room than the average ham.
After watching your video I immediately grabbed my Tiny SA Ultra spectrum analyzer, transmitted on 7 MHz running 100 watts into my homebrew 40 meter EFHW using my old Kenwood TS-180s and walked around my backyard viewing my spectrum analyzer. Using the supplied 12 inch whip on the Tiny SA Ultra my strongest viewed harmonic was on 15 meters and it was 50 dB below the 7 MHz fundamental frequency. This was a very unscientific experiment and really baseless because the RX antenna on the spectrum analyzer response to the fundamental frequency versus the harmonic bands is a big unknown and also the antenna pattern on the harmonics is not the same as on the fundamental (and I also was not necessarily in the "far" field). Also the transmitter itself generates harmonics.
I then repeated the above test using an attic dipole that's actually longer than a 40 meter half wave dipole and it's fed with open wire feedline connected to the balanced output on my old Heathkit SA-2040 Antenna Tuner and the worst viewed harmonic was again on 21 MHz and it was now only 35 to 40 dB down from the 7 MHz fundamental signal. Note that magnetic material also exists on the balanced output on the antenna tuner in the "balun coil", and there are likely lots of other non linear devices in my house that could have generated the strong harmonic content (very complicated topic), and I was not standing very far from my house during the tests.
Since there are so many variables probably the best "semi scientific" test would be to compare a true 40 meter half wave dipole versus a 40 meter EFHW antenna using the same transmitter as well as same spectrum analyzer setup and in that case the TinySA Ultra with its 12 inch whip antenna would be a reasonable device to use as you would just be doing relative measurements between the dipole and the EFHW antenna. Regardless of what spectrum analyzer you use you also need to make sure the fundamental signal is low enough into the Spectrum Analyzer to avoid generating harmonics within the Spectrum Analyzers mixer which would once again skew the results (I made sure the received signal on the fundamental was minus 30 dBm or lower into the spectrum analyzer in the above tests). The entire test setup should be in an open field.
P.S. I'm an Engineer in the rare earth permanent magnetic materials industry (for the last 37 years), and enjoyed seeing your use of Webers. During my University days we used units of Webers all the time for magnetic flux but that all changed when I entered the manufacturing world in 1986 where we used CGS units and we used CGS units for many years and never saw units of Webers, but then at some point the industry did make the switch over to SI units.
73,
Don (wd8dsb)
Thanks for your very detailed comment. The permeability of type 43 ferrite increases with temperature. As temperature increases the flux density increases for a constant volt-second area of the applied signal. My set up did not go excessively nonlinear until the core temperature reached about 70 degrees C. The variable gain of antennas vs frequency is why I used dummy loads for my tests.
73, Jim, KQ8E
@@Jimscoolstuff Hi Jim, thanks for the reply and I just stumbled upon your other video where you did the thermal test which was an excellent video. Thanks, and 73. Don wd8dsb
73 Don.@@wd8dsb
Very nice video, but since linear operation is the exception rather than the rule, it seems like any magnetic elements placed after the transmitter's output filters would have the same issues. I'm currently working on using QAM at VHF over an EFHW antenna for a military application, so I'm very interested in the work you are doing!
Note that between 30MHz and 225MHz the FCC rules are even more stringent. The power of any harmonic must be 60db below the power of the fundamental frequency. I have ordered a spectrum analyzer so I can get more accurate readings. I will make another video soon.
The FCC rules are for the output of a transformer or amplifier. When these rules were adopted, I don't think anyone anticipated a non-linear antenna. In my mind, an antenna is part of a transmitter, unless you are transmitting into a dummy load. Thanks for your comment.
@ats89117 Hysteresis is dependent on core material, distance from return conductor, frequency, etc. An air core would behave very differently than ferrite, for example.
@@jeremiahbullfrog9288 True enough, the air core wouldn't be subject to hysteresis or saturation, so it would be much more linear. But many systems use baluns and other transformer variants which are usually based on ferrite, and these also produce non-linear behavior...
@@ats89117 Yep i would agree
@@Jimscoolstuff Many antennas are using ferrite based chokes or transformers between the power amplifier and the antenna and I suspect these are all adding some degree of non-linearity. Maybe when you do your testing you can show that the EFHW antenna is worse than other antennas that include magnetics between the amplifier and the antenna.
Just goes to show why a lot of the ham bands are harmonically related, it means we to pee in our own backyards.
If he were transmitting in the SSB section of 40M (7.2 MHz) the second harmonic would be at 14.4 MHz. The top end of 20M is 14.35. The third harmonic would be at 21.6 MHz. The top end of 15M is 21.450. These harmonics would be out of band emissions.
@@skepticwest9628 I'm not saying it perfect but the bands where chosen for a reason and it was not to allow us to get more bands from one antenna. if you want to allow people to build their own kit it's better if for most of the time any harmonic issues don't affect other uses other than hams.
@@TheEmbeddedHobbyist I agree.