Why And How To Build An Easy RF Choke.
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- Опубликовано: 22 июл 2024
- For just a few Dollars to boot... An RF choke can save the day for field radio operations where you do not necessarily control all aspects of your antenna system and common-mode currents can wreck havoc on electronics, and even your fingers! Use an FT-114-31 with six turns of RG-174 or RG-316. You can also use eight turns with an FT-140-43. For more power handling you can use an FT-240-31 or FT-240-43 but I do not know the number of turns (RG-402). Do not ask me about other types of toroids, I don't know, and those are the best suited for the task. The choke is to be placed near the radio... Help this site: / radioprepper DISCLAIMER: The Radio Prepper logo (depicting a microphone) is indeed inspired from a famous flag created in 1775. It is NOTHING BUT a symbol of freedom and independence. It does NOT imply support to any political group. It does NOT imply, represent nor support any ideology with an intent on harming anyone. Freedom means freedom from persecution based on any human trait or belief such as, non exhaustively, race, gender, religion, sexual orientation or nationality. The Radio Prepper channel is a technology and science channel with a focus on preparedness and use of radio technology for disaster relief and small group communications in times of need. It is apolitical and open to anyone sharing the same interests. .
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Thanks for this Gil, I'm shack building at present so the timing was perfect!
Good project Gil, thank you. I think it is definitely a good idea to have one of these.
I was working a 200w station at a friends house he had a vertical and didnt believe in grounding. The heli mic touched my lip wile transmitting and man that hurt had me jumping out of my chair.
I love videos on RF suppression. Big fan of RF chokes. Good work Gil!
Thanks Josh, it's a really simple choke, aren't they all, and I just hope it will work well..
Well, you were right 👍 It's a good first project! Thanks for the information
Nice simple stay at home project, thanks Gil!
Can i use this on fm transmitter?
I see it. I see the inside of the box.
Always remember what my school teacher told us when doing homework or taking a test.
Neatness counts.
😄
The doctor is doing fine, too. Many thanks!
Good demonstration, many thanks for sharing.
Thank you for another great video showing us how to make an compact RF choke. Your awesome Mr Gil!
Another good practical video Gil.... Cheers
Such a good learning video, I watched it again.
Nice job! 👍🏻
I will never forget the feeling when common mode current at 100W on 40m into a short Vertical has hit my fist while started keying 🤯...learning by pain
Ouch! I never want to feel that!
@@RadioPrepper 1981, using an FT101ZD and a long wire....Ouch! is the correct term, I can confirm. Luckily, it has never happened since. Great vid Gil. 73 Keith
Always a good idea to test a new antenna on low power first. That way, you only get a little shock.
Oh yeah,the mighty random/longwire.
I've been using one as my main antenna for 5years now,I couldn't even count how many ridiculous anomalies I've experienced with it :D
I will definitely try a choke in the future
LOL, indeed. I wonder how many radios went back to the manufacturers that way..?!
That was very informative and useful.
Great videos Gil.
I used FT240 cores with 14 turns of RG58 for my home brew chokes. I have no problem with 100w, and could probably go much higher. --de N3TS
Why the heck would anyone give this video a thumbs down!? Good coin Gil. Thanks for sharing.
Thanks Julian. Some people disagree with that design. Some aren't gonna be happy if it can't handle a KW..
Great information!!👍
Vidéo fantastique! La réponse à mes problèmes! Merci beaucoup!
You can also wind the toroid bifilar with regular wire. Nice video gil.
Indeed.
Wonderful...Gil...
I really learned something. .thank you
Great stuff 👍👍
But did anyone else laugh at his RF choking his chicken picture in the video thumbnail?
Hilarious! Thumbs up for great information and some fun too!
Toujours chouette. Merci! :)
Thanks again. Very informative video. I have
an endfed antenna. Was getting RF feed back so bad that it blew my GFI in another room. Come to find out my coax was bad.
Thanks again. Clark KG7LOI.
Well done, nice project 👍
For a RF shoke it's simple. Independent of the both materials that you recommend put as much turns around as you can. For QRP power RG174 or RG316 is perfect as you can put a lot more around. It's simple as that. Despite a choke I prefer a 1:1 wired BALUN directly connected to the feedpoint of the antenna. If using balanced ladder line for feeding the dipole I place it on the junction between ladderline and coax feed. Every time as close to the antenna feedpoint to avoid coax loss and detuning of the antenna due to the coax feed. Also the ATU, directly behind the choke (1:1BALUN) to have low coax loss and best impedance matching between antenna and the 50 ohm coax.
Very good thanks!
Nice project Gil! If you're stuck with rf on the outside of your coax, I just use a 110mm diameter waste pipe to form a coil of 8 to 10 turns in the feed line. It forms a simple choke & I then either tape it up or use 4 zip ties to hold its shape. Take the waste pipe former out & you stop nearly all of the return current. I usually put it about 1/4wave, on the lowest freq band you are going to use, down the feed line from the antenna. It's cheap, it's nasty but, it works. Not as small as your one but does the same job. I usually do it on RG 213, 1/2" coax.
Certainly, but it isn't called an ugly balun for nothing ;-)
Radio Prepper true! I’m using 200W or 600W so it needs to be a bit clunky though. If I used a toroid, it would need to be quite a bit bigger & much heavier than the coiled feed line. Horses for courses. I still like your one though neat & has its place. I gave an FT817 too so I can use it.
Good point for QRO...
Thank You!
Use 21 winding with RG316 to make a good CMC. Toroid used is FT240-31. Handle easy 500 watt !
Thanks. FT-240 is too big for me. That's a lot of turns!
I made a 4:1 balun, didn't know what I was doing and it works,hi hi
Thank you.
Hello!. Im new to HF and was recommended to purchase this antenna. If you have time, what do you think of this. (I got the 155-foot with a 100-foot coax and instructed to choke at 95ft from antenna connection. Supposed to be good from 160m-6m..Thank you!
I wonder if it would make winding the toroid easier if you hot glued the first wire wrap to the toroid. Thanks for the videos. I'm always learning something new from them.
Maybe a tie-wrap temporarily...
"I'll be amazed if I don't burn myself" ....me, every time the soldering iron comes out lol
LOL yup.
You what a common mode choke on every antenna because no antenna is perfectly balanced. Yes some antennas have much more unbalanced than other but there is always some stray currents. So use a good common mode choke and you will happy that everything works.
I only use mine when needed...
Great vlog Gil, can you post a link for your electrical boxes you are using for your kits, please. Thanks for sharing.
Hi, they are Hammond cases..
@@RadioPrepper Thanks for the reply Gil. Excellent.
Hi Gil, do you have a video about that magnetic loop behind you? I would like to build one for my balcony, mainly for 20m.
Yes, search in my videos..
Thank you for the nice video. I want to make some RF chokes for 'listening' on the VLF and LF bands. How can I determine which toroid I need, and especially, how many windings are the right amount? -Thanks.
There is a document floating around with all that info... Not sure where it is though. I think it was posted on one of my videos..
Tnx. 73.
After watching your videos on the Minion I got to wondering if some of the problems I experience with my homebrew radio and random wire are due to common-mode currents. That made me wonder what you use as a choke. Then you do this video to explain! Merci beaucoup Gil!!! (are you a mind reader as well as a radio prepper?)
If only I could read mine sometimes ;-)
Great video - thanks! So - if I have my FT-891, I'm outside (not trying to operate QRP in a hotel room as I often am) and want to go full 100 watts, what has to change? The toroid? The coax? Both? I love the idea of the small size and I can both pack in a bag for travel on in my saddlebags when on my motorcycle. Thanks in advance for the help. 73
The toroid, FT-240-31, bigger...
Hi, thanks for the video!
Curious why you chose coax and not bifilar?
And also, is 140 size good for QRP only? I use 240 size rings for 100 watt chokes.
73!
It's just simpler and bifilar is more finicky, requiring more attention to detail..
Tnx👍🏻
Great video. Thanks.
73 de Kevin, VK4KK
Thank's
Salut Gil, as tu une idée des performances de ton choke comparé à ces graphs (trouvés via DX commander)?
Non, je sais juste que ça marche. Il y a certainement moyen de faire mieux.
Gil you have convinced me to put up a half wave antenna for 20 meter cw. I need your advice. My shack is on the 2nd floor of my house. I have access to a water pipe earth ground. Do you think I need a counterpoise? If yes, where should it start ? Thanks for your videos.
No.
Good morning, is this worth using when shortwave listening? Thank you. Stay well, 73 Lee
Yes, absolutely, though the tuning button is a bit small, but great using CAT control with a computer.
What's the model of the CW paddle shown in 3:35 and where I can buy it?
www.americanmorse.com/dcp.htm
Hi Gil, Can I use the same principal and turns for the 11 meter band 27/81 FM ?
Bonjour, oui.
Gil, how about a video on using a nano-vna for antenna analysis? (Please)
I would but I can't really afford one right now..
Sir great video! I am new into HF. I got one of those Sigma Euro-Comm Vertical antennas that don't use radials. Do you recommend I use an RF choke with this?
Only if you notice problems...
Is it correct to wind coax cables at radius smaller than datasheet explained ? I mean bending radius.
Not the best...
Is a choke/1:1 balun necessary for a random wire antenna with a 9:1 unun for 80-10 meter 'receive' only?
No.
Maybe you can help please. How many turns have a RFC coil for FM tube radio with ECC81 and what is the diameter of wire in mm and the diametere of the core? i have found that i use 37 turns of 0,8mm wire and 8mm core bat i think its not right. Have any one an idea?
Sorry no idea.
where can you order the FT-114-31 core? I tried ali-express but could not find. any hints?
Ebay, but the FT-140-43 is easier to find..
can you just wrap a sma cable around a toroid, no soldering? also how does this suppress DC? Wouldnt you want a 1:1 isolation transformer?
Hi, sure. It does not suppress DC, just Comm9n mode currents. Not sure which of the two works best..
I have 240-43, can I wind one that will cover 160 to 6 meters using that 240-43 and RG58? How many turns would I need? Thank you for the information. 73 de W4DES
I would try a dozen... I have seen sites online with netter information though, worth a bit of a search...
what would be the max power on this, I would imagine the smaller coax couldn't handle 100w.
No, definitely not..
Hi! I have a question for you. When using an End Fed Half Wave antenna with a 1:49 unun, do I need a choke balun, or is it not necessary in this case?
Generally not necessary. You would need one for a 9:1 with a random wire though..
@@RadioPrepper Ok, thanks. 73!
Hi Gil, I love your videos. How you did you determine that you need 6 turns?
Hi, I must have read it somewhere. It might not be enough...
@@RadioPrepper I guess if it works then it's all good. I only ask because I am studying for Extra in the US and trying to get deeper into theory. Thanks again for the amazing content, sir!
Are these types of filters ONLY for unbalanced antennas or will they remove rf noise picked up from power lines also?
Not from powerlines. You'd need a specific filter for that, not sure what kind...
Gil, nice info! Congrats! Can a FT-114-43 be used as a choke? How many turns? I've made a 49:1 with 2 x 140-43 and like to know which choke fits better. 73 de PT2YW
I would say yes. I would actually use a few more turns, say, eight to twelve, experiment...
A sign of RF issued would be when TXing on HF your computer speakers start buzzing? (Using a 20m EFHW antenna)
Put your tongue on the coax shield?
@@RadioPrepper not sure thats a good idea :-)
Hello Gil I've used epoxy to glue toroids down into boxes for chokes and EFHW transformers but just enough to hold it in place rather than potting the whole thing however what I do is wrap the core in loads of PTFE plumbing tape first that way if you want to take it all apart later you can just cut the tape off and the toroid is free. I've often found hot glue doesn't stand up very well when when you throw it in your kit bag. A few knocks and things just tend to break loose again. I built one just like this however I put the connectors on the same end of the box so it packs away a little easier.
Great, yes, that works!
Bonjour gil de radio prepper.
Est-il possible d'accorder l'impedance d'une antenne dipole "pour le 11m "de 71 ohms au centre avec un coax 50 ohms en utilisant un balun à air.ou la desadaptation mineure ne nécessite pas vraiment ce genre de montage.
En effet pas besoin, c'est assez proche..
Just ordered my toroid on Ebay, curiously from a french seller...
And I order from the UK!
Where can you find the FT-114-31? Cant seem to find it anywhere.
Apparently I got a non-standard Chinese-made one.. Get the 140 size..
Nice. What antenna analyzer is in the video ?
EU1KY model.
I leave my portable connected to my random wire antenna and today I noticed none of the buttons worked. I took out the batteries and it worked for a few seconds and locked up again. I unhooked the antenna and now its fine.
I wonder if this was an rf issue or because it's a cheap radio?
It is stormy out today if that'd matter.
Hi, that sure sounds like it... Try with a choke, you'll know right away..
I think I can do that if I slow down the video and spend an afternoon studying. One question I have is where o you get those neat little boxes? Who knows, I may build one of these. I have hand tremors and had an awful time with Anderson connectors, an awful time. Thank you for your video. Looks like there were a lot of people who needed this information. It was kind of you to help so many. N4KBM
Hi, I get them on Ebay for the cheap stuff, and the good ones, the Hammond brand.
@@RadioPrepper What size is the box?
Can't find an FT-114-31, google shows nothing, any sources?
FT-140-43 are easier to find..
Hi Gil, can you advise on an EFHW transformer using 140-43 cores? What size wire did you use and was the turn ratio still 14:2? And did you use the standard 100 pF capacitor?
14/2:for upper HF, 21/3 or even 24/3 (64:1) for lower bands. 100pf 3KV.
Wire: 1mm.
@@RadioPrepper TNX ES 73!
Thanks for your videos they are some of the most useful on U tube for the Ham types especially beginners like me. Your English is great thank you again. KI7RJS
Thank you Don, much appreciated!
shouldnt the test check for the S21 attenuation? SWR doesnt say much
S21?
Must one use coax? Is there any reason one cannot use, say, twin speaker wire, or a manually closely coupled bifilar winding?
Coax is just simpler and bifilar is more finicky, requiring more attention to detail..
@@RadioPrepper A perfectly reasonable reason :-) I just don't have any thin coax like that, but I have some flat, four-conductor single copper stuff from Radio Shack; I'll split some of that of into two pairs: it'll probably wind easier and flatter anyway.
Keep 'em comin', Gil, I look forward to seeing notifications of your new posts in my inbox.
Anecdote: I miss France, too: an ex-pat Brit in the US now for 36 years, I used to travel around western Europe for my job back in the late 70's, back in my machine tool controls days. The inside of a French tool & die shop is the same as any other, but the surrounding countryside was beautiful. Do you guys still have yellow headlamps? I always though that was smart... (priority to entry onto a roundabout not so much ... ;-) )
This must be for a qrp transmitter ? I've seen more and more recommend the 31 material.
Hi, yes, and yes :-)
Is the number of turn very significative ?
some poeple are sujesting 14 turns.
Is there a way to measure it with a VNA ?
73 et merci d'avance
I think more would indeed work better. You can measure its impedance yes.
Bonjour Gil! Where do you buy your toroids from?
Kind regards, Simon
Ebay..
Gil, you rock. Question, is that toroid providing enough resistive impedance for 80 meters, without the inductive impedance? I just finished a 240/31 w/17 turns, but always looking to save ounces. This choke is now the heaviest thing in my kit except for the radio. 🙂
I think around 900KOhm...
Oops, 900 Ohms sorry.
Thanks. How do you know/calculate the correct number of turns, or is this purely trial and error?
There is a calculation but I just got the info from a few different sources...
One source, I have used and think is very good is G3TXQ's findings on common-mode chokes. It can be found here:
karinya.net/g3txq/chokes/
@@RadioPrepper - and those sources are dead wrong. You should remove this video, because a.) wrong number of turns and b.) such a core 'FT-114-31' does not exist. So, what you show in your video is just 'believe'. ;-)
is these better than 4-5 ferrite beads?
I haven't tested...
Thanks for the video. I just build an 9:1 UNUN - inspired by your videos. ;)
But I have a small question: Would a FT 114-77 also work?
I don't believe so, but not sure.
Hello! Can you please tell me if the FT 114-43 can be used?
Yes, but given its size I would use 3 turns primary, 21 total, even 24 total for 30m and below.
I even use the FT-82-43!
Chameleon makes a coax cable with a choke built in to one end. Does it matter which end of cable is connected to the radio for HF or VHF/UHF?
Better locate the choke closer to the radio.
It just depends whether you want the shield of the coax to radiate or not.. With a randon-wire end-fed you would. With a dipole, not.
OK, and with the Mil 2.0 Vertical, I would suppose you would want as much energy out on the antenna itself. I initially kept the choke out by the antenna, but now have the choke at the radio, mostly to keep the RF away from myself.
That's the way I use it...
I was wondering, after winding a choke yesterday, can you put the choke in the same casing as the balun (or unun) or will that have unwanted side effects ?
I thought about that issue and am guessing that a bit of separation, at least a few inches is better. Maybe just using a longer box and putting the toroids at opposite ends might work.
I was thinking the samething.
While placing the choke in the same box as the balun at the feed point should do no harm and should help, typical practice is to place the choke away from the antenna. The idea of the choke is attenuation of common-mode current. One theory is to put the choke one quarter wavelength back from the antenna feed point. Just as an example, if you had, say, a doublet with a 9:1 balun at the centre feed point and it was fed with RG-58U co-ax. If you were operating on 20m band, you can calculate the wavelength as 300/14.1 = 21.28m. The quarter wavelength is the 21.28/4 = 5.32m. However, you have to take the co-ax velocity factor into account. This is usually 0.66. So, 5.32x0.66 = 3.51m. You would put the choke 3.51m back from the feed point.
Simplify the above by using one formula for RG-58U:
(75 x 0.66)/(frequency in MHz) = quarter wave distance in metres.
If you have a different type of co-ax, just replace 0.66 with whatever it's velocity factor is.
For longer runs of co-ax, you can place the choke at odd multiples of a quarter wavelength (one, three, five, etc.).
@@Steve-GM0HUU
I'm not sure why you wouldn't want to place it as close to the transmitter as possible? Isn't the feed line considered part of the antenna if it's some fraction of the wave length you're using? I've got EFLW's on the brain, so I'm pretty sure what ever I say my be wrong here.
@@Steve-GM0HUU In certain cases you may be correct Steve but in most cases I would suggest that people use common mode chokes to stop ANY part of the coaxial cable becoming part of the antenna. Allowing your coax to radiate for any multiple of a wavelength will only serve to alter your radiation pattern. That's why common mode chokes are placed at the antenna feedpoint, to stop RF currents coming back down the outside of the coax and effectively becoming part of the antenna.
How could epoxy disturb the magnetic field... unless you used filled epoxy like JB Weld.
I wish I knew... I tried twice...
Nice and simple project, but is the hot glue necessary?
You have to secure the toroid one way or another...
@@RadioPrepper Thad makes sense. Thanks.
How many turns for 30 - 10 meters for FT114 31?
No idea...
@@RadioPrepper thanks
Nice job! Just ordered toroids from eBay, 140-43 2pcs. I was planning to make 1:1 balun for my dipole and
maybe 49:1 for end-fed, what you think?
Where did you get those little plastic boxes?
Tnx, 73!
Sounds like an excellent plan. Boxes are from Ebay: www.ebay.co.uk/itm/264683896396 but the Hammond 1594BSBK is much better...
Do you think you still need an RF Choke when using a End Fed Random Length wire with a 49:1 balun? I haven't seen RF Current, however, I can't say that I'd know what I'm looking for since currently all my work is SSB or FT-8.
49:1 is for half-wave wires. 9:1 is for random. You never use a random wire with a 49:1. A half-wave wire should not require a choke.
@@RadioPrepper
Interesting, I'm making and using 49:1 for EFRW antennas and getting really good SWR's across all the Ham Bands from 30Mhz down. Normally I get SWR's in the low 2's
@@TheDgdimick Curious. What cores are you using? for a 49:1 I've found -43 to be pretty good however -2 (powdered iron) is very lossy and you might see a decent SWR but all your energy is just heating up the core. Build two identical transformers and hook them back to back. Transmit into one end and connect the other to a 50 ohm dummy load via a power meter. Measure the power at the far end versus the power you put in. If you put 10w in and get 5w out like i did with -43 cores then each transformer is losing about 25% of your power as heat. I did this with -2 cores and could barely measure any power at the far end they were so lossy.
I should mention I use -2 cores for chokes because unlike an autotransformer you actually want the core to burn off any common mode energy as heat
@@binky_bun
Thanks for your reply, and bare with me here:
I'm using 240-43, for the 1.5Kw (3 of them) 49:1 baluns, and 140-43 (1 of them) for the 100w or lower baluns. Now, I'm not disagreeing that there is some lose, I just have an issue/question about your test when using a dummy load. Most dummy loads are 50ohms, when you use a 49:1 balun your only going to be seeing an input of 1.0 ohms = 50/49 = 1.02 ohms, and a 9:1 balun will see 5.56ohms, into the transmitter. The BAD SWR you're feeding into the transmitter should/will cause the transmitter to decrease the power the transmitter outputs. I see your test as not really being valid. If I was going to run your suggested test, I would need to build a 3300 ohm dummy load, however I don't have 10watt resistors to do this. If I'm wrong here, please correct me.
Did you have power meters on both the Transmitter output as well as on the output on the balun? Just because you dial in 10watts out on the transmitter doesn't mean your going to really get that 10watts out.
Just a little bigger box, little bigger and a ton of hot glue. Lol
Tu es sûr que c'est ft114-31 et pas ft114-43? Je ne trouve rien sinon...
Ou 140-31, pas sûr, le miens est un "made in China," pas standard..
9:1 unu. Work on non-restence freq. Bc u want this bc u don't want Short of open . Bc mine has 55 135 141 203 are lenght it dose 10 to 160m.....
I didn't quite get that sorry...
Salutation gilles.c est bien ce le tu fais -ancien f-60194 hugues
Merci. Gil.
Jai rien compris, mais j'ai regardé comme même.
Hot glue is great but I try never to span a live to an earth with the stuff (i.e to use it as an insulator). I have seen too many cases in the workshop where glue has browned over time and become conductive.
Good to know thanks!
@@RadioPrepper Good man, great channel and wonderful videos.. Thank you.
What would happen if I hooked this up to a 2m radio?
Not sure but why would you?
@@RadioPrepper say if I threw a random wire up a tree and got heavy swr???
You never use a random wire for 2m and it would not help SWR anyway. Look into a coax colinear.
@@RadioPrepper was just thinking of a hypothetical where you may try it to get an emergency call out
It might work but I would guess no better than the rubber ducky the radio came with. A ladder line Slim Jim would also work much better...
I can't find a FT-114-31 anywhere. de W4WLC
Apparently it's non-standard, probably Chinese-made. Better use the next size over, like 140 maybe..
@@RadioPrepper Thanks for the fast reply. Think I will go with the FT-140-43...
That'll work :-)