G4NSJ - Common Mode Chokes NanoVNA Coax
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- čas přidán 7. 04. 2021
- In this video, I check out Common Mode Chokes with my NanoVNA. I also reveal some interesting facts about coax and the so-called flowerpot antenna. Plus, checking quartz crystal frequencies with the VNA.
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www.radio-workshop.co.uk/g4ns... - Věda a technologie
Thankyou, fantastic demonstration. I've gained a bit more knowledge which helps in my current project.
Ignore those who complain about rambling. My understanding of what happens when you cross the winding over on the core so the output is 180 degrees opposite the input end is that it's exactly the same as a continuous winding where both the input and output ends are next to each other. If you think of the toroid as a solenoid ferrite rod so you effectively cut it and bend it straight and think of the common mode currents from a DC perspective it makes it much easier to visualise what's going on. If you have a straight ferrite bar and wind a coil around it from top to bottom and pass a DC current through it you create a magnet with north at one end and south at the other. You can change the North / South pole orientation by either flipping the direction of the current or by winding the wire in the opposite direction which are really the same thing anyway. Now think of that crossed over toroid bent straight. The turns still go in the same direction except rather than the ends being at either end of the rod there's one at one end and one in the middle. Say we wind up to half way from the bottom then go right to the top and wind back down to the middle in the same direction that's exactly what you have if you straighten that crossed over toroid out. The turns still go in the same direction around the core and at DC the north / south orientation is the same. In the AC world the north/south orientation within the toroid is trying to flip back and fourth but the hysteresis of the core soaks up that common mode energy as it tries to flip the magnetic direction within the core. Maybe I should make a video on it one day with some visual demonstrations. A lot of people seem to get hung up on how crossing over the windings on the core affects the action of the choke and it takes a lot to visualise what's going on but it really doesn't make any difference.
Thanks, Ben. Great explanation. Cheers, Ray.
Thank you for the lesson. Just bought a Nano VNA-H 4, looking forward to the next lesson.
Regards and thanks
Great stuff, Ray. Fascinating topic, really well presented. Many thanks! 73s, Charlie
Thanks!
Great video Ray. You did a great job explaining common mode current chokes. :) 73 Joe P.S. Don't forget to water your flower pot antenna!
Thanks Joe. I water the flowerpot every morning! Cheers, Ray.
The right hand rule gives the direction of the flux in the core. He reverses the direction of the turns in order to make the coax come out the opposite side of the core. The cross over allows both sides of the core to contribute to the amount of inductance.
Great video. You always come up with something interesting to talk about and answer questions I've had for years. Since subscribing, your channel has become part of my CZcams play list and I look forward to learning something new every day. 73 DE KG2RU
Thank you, Bob. That’s very nice of you. Cheers, Ray.
Very informative ramblings!!! Love the videos
Thanks!
Thanks, Ray, I really enjoyed a couple of your workshops. And I will be listening in the future, too! Take Care my friend. Be Safe. Sincerely, Howie C.
Thanks, Howie. All the best, Ray.
Since i've only just bought myself a NanoVNA, i'm looking forward to the next video.
Very interesting.
I believe that not only the number of turns is of great importance, but also the polarity of the magnet ring. Electromagnetic fields are arranged in a specific way. Therefore, further tests would be interesting, when the ring is set in reverse polarity and when the coils are wound in one case and in the other case in the opposite direction.
The toroids are not magnetic, interestingly they have a very high electrical resistance and are almost insulators. Only -31, and -43 (or direct equivalents) should be used for HF chokes.
Really enjoy your content and the presentation. Thank you.
Thanks, Susan. That’s very nice of you. All the best, Ray.
Thank you for the explanation ray great stuff. Gary
Thanks!
Excellent video. Thanks.
Great job explaining! Really enjoyed the video.
Thanks!
Fully understood what you told us, Ray...more blackboard theory..he-he...do enjoy it when you get the blackboard out...( Mike, Ruislip.UK )
So, I think you explained it very well.
Thanks Ray!
73
Thanks!
Thanks Ray, another example of how to present radio related techniques to "most of us" "Exemplary". 73 Tony G3RJ
Thanks Tony.
Hi Ray. If you're waffling, then you just keep right on waffling along my son! - Let me tell you Ray, I've learned so much from your chats and descriptions of how things work, much more than I learned along the way on my amateur radio courses to get my license. Many thanks Ray for making these videos, and the clear easy to understand way you have of explaining things.
If that fool that doesn't like your style of presentation, what's wrong him, is his finger paralysed and he can't click away? Then it may be his brain that's paralysed! It's not hard, if you don't like something then don't watch it!
Also, by the way, I also enjoy you stories too. Liked hearing all about the ghostly voice on the CB, about that time you found that pirate radio transmitter and the time transmitting from a boat just of the shore, with the DTI blokes looking for the transmitter on the beach.
Regards, David (M0XQZ)
Hi David, thanks for your kind comments. It's nice to get positive feedback. I hope all is well with you. Cheers, Ray.
G3TXQ's work was excellent, sadly he is SK now, common mode chokes are wonderful things nice to be able to run QRO without RFI...fwiw I got a "peak" of about 35dB at best, very close to your results. I used a teflon insulated coax, but now using a total of 6 cores. One thing you can try to gauge the effectiveness when you have yours boxed up is to part pull the PL259 out of the socket on the radio side so that only the centre pin is making contact, it should go very deaf, receive will of course come back when you screw the collar back on.
Thanks for the info.
Great explanation of how the RF "spills" out of the unterminated end of the shield back down the outer part of the shield and then terminate with the choke to provide the other half of the dipole. Never thought of it that way, As for how you wound your core with turns one way and the same number of turns the other say, that is the way a company here in Texas called, Balun Designs, winds their chokes that I buy and use that work great. Good video. 73 WA4QGA
Thanks, glad you liked the video. Cheers, Ray.
Good demonstration,
I understand that stacking toroidal and using a high temperature coax it will allow you to increase the wattage without damaging the coax. I normally use RG400 coax.
Yes, I believe that’s right.
Nice video Ray with some good technical tips and a pleasant fireside manner. 73, Jamie VK2YCJ
Hi Jamie, I’m glad you liked the video. Thanks for letting me know. Cheers, Ray.
Great video my man! Thank you for the explanation! I now know how to easily make a balun
Excellent!
Cheers Ray, gonna have to get myself a nanovna to play about with !!
You won’t regret it!
Hey Ray, enjoyed the video. The fact that you actually marked your dark box as such had me in stitches. While I enjoyed the video, it has me a bit perplexed. I was under the impression that this sort of measurement is supposed to be done as a THRU measurement, yet I see that you measured as an S1 reflection measurement. And even if that were acceptable, wouldn't you then need to cut your measurements in HALF because with a reflection measurement, wouldn't the signal be attenuated twice, once on the way out, and once on the way back? An illustration of your test setup and explanation of your methodology would have been helpful. In any case, cheers from Los Angeles.
I see what you mean. I'll have to look into that as it's some time since I made the video. I'll watch it and have a think.
Excellent explanation Ray full Marks Mate Ian VK2IJ.
Thanks!
Great stuff .
Good stuff! Enjoyable.
Thanks!
Good info to know. 👍🏻
That has increased my understanding of the choke. The measurement of the size of a toroid is in1/100 of an inch in diameter (I think).
Thanks!
flowerpot antennas probably have square roots lol great dad joke love it mate
Haha, love it!
Thank you thank you thank you! Subscribed :)
The difference between AF engineering and RF engineering:
At audio frequencies, what happens at one end of a piece of wire is much the same at the other end.
At radio frequencies, all bets are off.
Nice video Ray. 73 de M1GWZ
Thanks!
love your videos :)
g
i started laughing at the flower pot square roots joke and thought to myself christ there's no hope for me now, thanks for the demo EI6IKB
Happy days!
Staking the cores increases the power capability, not the inductance.
Glad you called them clip ons and not strap ons. 😂
Haha, indeed!
Mix 31 is good from 1 MHz to 300 MHz.
Excellent video, new subscriber!
73, N1WOM
Thanks John.
Nice...👍.
Thanks!
hello ray did you hear about more medium wave closures this is saddening as i don't wanna go online to listen to radio
Yes, I’ve heard of more closing down. It’s a great shame. Such a loss.
What is strange about the currents are split between inside and outside of the braid is that this fact is constantly discussed but who cares if it's right or not. If the currents combined or stayed separate, it makes no discernible difference. I also have never seen a proof that the currents stay separated with some kind of tests. Never seen it.
Ok I take a choke found at radio shack® and make a quick short wave radio. One end goes to earth the other to antenna. The I ground one end and throw about ten turn with a 365 variable cap to a diode to a lm 386 af amp cheep short wave yes chokes can do tricks tks
Great idea!
🤜🏻👍🤛🏻♡♡♡
Like Ape says: Toe-roids ;)
......Yes, skin effect is a fact, but, its also frequency dependent.... as a military trained telecomms engineer, we were taught 'skin effect' was not really important, below a Gig, or so......
.....Oh, & if you want a waterproof box for your FT240-43, check with your local electrical supplier, you can get waterproof junction boxes for a quid, or so!!!!
Thats interesting, because the benefit of Litz wire is lost above 2Mhz due to skin effect...Turn that around, skin effect is exceptionally important above 1 Gig, so probably an issue of context, rather than fact.