RF Chokes And Why You Might Need Them
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- čas přidán 21. 07. 2024
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Due to the skin effect RF only flows on the surface of a conductor. A typical coax feed line is effectively 3 wires: the center conductor, the inside of the shield, and the outside of the shield. An unbalanced coax fed dipole without a choke is effectively a tripole. The outside of the shield sends RF back down the coax into the shack and also interferes with the radiation pattern of the antenna. A common mode choke at the feed point greatly reduces or eliminates this. However, the outside of the shield still acts as a receive antenna picking up radiation from the antenna and noise from nearby electronics in the house like the cheap switching power supplies used in wall warts. A 2nd RF choke at the radio helps eliminate this. So adding a choke at the feed point and just before the radio can lower the receive noise floor depending on the source of the RFI. Some consider this one of the best kept secrets in amateur radio.
In most cases the source of receive RFI is actually coming from inside the house. A good technique is to turn off the power for the entire house while running your receiver from a battery to see if it lowers the noise level. Once you've determined the noise is coming from inside the house, you can turn off individual breakers to isolate the circuit and test individual devices including LED lights.
Every situation is different but if you are experiencing RFI it's worth running the experiment. 73, K1AV
I just added some of the in line chokes from ABR Industries at my radio last night for each of the antenna inputs. Unfortunately my noise floor is so high due to power line noise it didn't do much at all. But, I did sort out the noise coming from my speakers. I put a big ferrite clamp on the 3.5mm audio cable coming from the computer and wrapped it a few times. Knocked out the RF completely when I TX with FT8. So I got that going for me.
The “ground bracket” is for lightning safety, and the choke is for common mode current impedance. If he uses a choke at the right before the coax enters the shack it won’t hurt anything. It will just suppress any stray CMC.
A ground bar or better term “Earthing bar” is only for safety, and will allow static charges and lightning events a path to earth and NOT THROUGH YOUR HOUSE. Single point earth “grounds” is an entirely different subject and consulting a licensed electrical engineer or electrician would be wise. N0AX has an excellent grounding and bonding book which is sold by ARRL and would be a good starting point for proper safety techniques for the ham shack.
Very informative. Thanks.
If the antenna requires a return to ground, like a 1/4 wave vertical, then a grounding block before entering the shack will help with stray RF, station safety ( National Electric Code ) and lightning protection. If the antenna doesn't require a return to ground, for example, 1/2 wave dipole, endfed, etc, then you need the common mode choke on the feedline. That is to say, the station ground is a must for safety, lightning and stray RF, but depending on the antenna, like examples above, it's probably not enough. WP4AOH ARRL Technical Coordinator P.R. Section.
FALSE. THAT ISA GROSS VIOLATUON OF NATIONAL ELECTRUCAL CODE 2011 ART 250.24(a)(5)
Code FORBIDS you to ground that coax AND connect it to a radio.
Thanks for another very informative video
A choke at your radio and at your antenna is best practice. Keep your transmit power inside the shielded coax. Not on the outside.
loved that question and answer at the 8 min mark oh wise one.
To answer the third question of grounding the outer shield is…yes. I have 3 EFHW, antennas at my QTH, and every one of the runs of coax goes to a polyphaser that connects to a ground rod outside of the shack, then another run of coax into my shack, took care of my RF no problem without using any chokes. I bet it would help you out with your RF mike. Thanks for another great video. And Ham on !
thank you for that answer. I like your conclusion. It fit's my world view!😉😆😁
@@AlvinMcManus not sure what you mean by that last part. but it’s simple ,it works and it’s part of the NEC
When in doubt Choke it . Grounding your coax before it goes into the shack Is always a good idea, but common mode current on your coax will make the coax part of your antenna You're antenna is not designed to be that way And you need to get a choke Where the signal leaves tthe coax to the antenna Remember guys Balance antennas And unbalanced coaxial Won't work properly together without Some means stopping the flow on the outside of the coax Coax is a 3 conductor, Rf flowing on the outside of the coax Will Radiare signals and transmit Vertically Off that coax This will destroy the radiation Pattern Of your antenna So placing a choke at the antenna Is always the best move .
I'm sure that grounding the coax shield will help with both common mode current and RFI. It's also a very good idea to also incorporate a lightning arrestor into the system.
Have to wait another three hours...but I am looking forward to this one!
Those band pass filters look nice!
On your DX commander, I would put the choke at the entry panel, rather than the feed point. The outside of the shield between the feed point and the choke will just act as another radial. With the choke at the feed point, the shield is in the near field of the antenna, and your transmitted power will induce current on the shield, so you can still get RF coming into the shack. I put mine just inside the entry panel, protecting them from the weather, the deer and the turkeys.
Meow!
Love them band-pass filters. with the end fed half wave question, yes the ground rod with surge protectors will also bring shield RF to the ground rod. like in picture. this goes out side at the point where the coax comes in. also out side connect #6 stranded bare copper wire to the house electric ground rod and burry the wire. now in your shack make a single point ground. ether a copper pipe or buss bar . mount eater on wall or desk what ever works best. get some ground strap from ABR or DX engineering. tined copper braid. put a piece from ground rod to the singe point ground behind shack. now run a ground braid from each piece of equipment to the single point ground . like radio, power supply ,the amp, what ever you have. this also will may help Mike K8MRD with the RFI problem he getting. if you add choke on coax that is ok. wont hurt . radio or amp side. after the ground rod. hope this helps. that pic of ground rod with protectors is what to use. . hope this helps .! it helps me with my snow static problem I get in Boston NY. 73's
Hey Mike... great video, I killed my subwoofer amp in the living room because I had an EFHW too close to that part of the house.
I was working some 10 meter ssb and my wife said she was hearing me in the subwoofer and it sounded spooky but then it went away haha no doubt when it got smoked!
I have chokes on all my antennas...dipoles, DXCommander, and hexbeam. Not sure if they really help but I figure it can't hurt. Even with the chokes, still have problems with computer speakers and touch lamp when using the hexbeam, which is about 3 ft. above the roof, and 600 watts with my amp. Solved the problem with the touch lamp by unplugging it and found that better quality computer speakers really help.
Had a tuner in line dealing with high VSWR. One day I was cranking the inductor with a metal handle and noticed my thumb was smoking. Callus so no pain. Yeah...common mode problem.
I was advised to run speaker wire as a ground wire up through the house from my cold water pipe to all my radios to help ground
Yes, grounding the shield before coming into the shack will help with keeping RF out of the shack. Also can help with noise.
Do it.
Steve, k7ofg.
I use a choke at the Antenna feed point and a Alpha Delta TT3G50 at the ground rod before entering the house....
As to the question at 7:30 min... The choke is like a cork in the bottle.... The ground rod is like a drain hole to let the wigglies fall out before coming into the house. Essential for lightning protection, but some RF can still sneak in.
As far as lowering a noise floor, couldn’t you use a lightning arrestor with a ground lug and use that to lower the noise down a bit.
I have lightening arresters on my EFHW, and need the common mode choke after the arrester. That's different than the grounding block. I'm too far away from the ground to use a ground block like that. The fear is my ground wire is close to 1/4 wave to the HF bands, so it would cause more noise. If he's getting RFI when he transmits on the EFHW, the block isn't working...
My mobile setup is choked fairly well. BUT my computer mouse misbehaves when I run FT8 on 20m only. I have no weird noises... just a tiny mouse glitch. I've since choked my computer's power and data cables. I think all is good now, but more chokes is never a bad thing. I need to add more chokes... more chokes! HAHA! Scott, KE4WMF
The grounding with a EFHW and a choke, meh, try it and find out. I run a 9:1 with a 29ft piece of wire for a 40-10 antenna and I don't have it grounded, LMR400 right through the window and into the radio, not even using a CMC at the radio like one would, but I do have a 11ft counterpoise on the UNUN.
Remember if you're choking be sure to know the heimlich maneuver HEHE ;)
A definition of "common mode current" would be helpful. It's simple. It's all the current on feedline that isn't signal you're putting there from the transmitter (on transmit) or the antenna (on receive). For example, It can happen at the antenna end of a dipole from an imbalance between the halves of the dipole (slightly unequal lengths, coupling with house siding on one side and not the other, etc.) so the alternation +/- in the feedline is not perfect. The difference shows up as common mode current.
It can be some kind of RFI from power lines. Feedline is a perfectly good antenna for that kind of stuff. So a choke at the RX end *can* help. The feedline can easily be an antenna for all sorts of random electromagnetic crap and will happily pour it into your RX. A choke at the radio end will help block that extraneous crap and actually help make a quieter RF environment for you.
Is common mode actually radiated by the feed line? Is it important to have the choke outside the house/shack? Or is it only running on the feed line so an inline choke at the radio with the antenna coming into it is sufficient to keep it from entering the radio and any attached equipment?
@@scotch8 Common mode current flows along the outside of the feedline. A choke at the shack end will prevent it from coming back into the radio. At the antenna end it will prevent common mode current produced by an imbalance in the radiators to flow back. It won't help with garbage RFI picked up by the feedline at the RX end. In short, it's not a bad idea to have both.
Loop on the ground for a receive antenna is the way to go my InFeD halfway Vantana S9 noise from the floor loop on the ground an S3
Shouldn't need choke with grounding setup outside. But if you go mobile you would want one then.
The problem is : endfed antenna.
This kind of antenna simply doesnt work.
How to feed a bulb filament only by one end???
Altough the filament is shining ! In orher words you make contacts with this antenna....
Ask yourself where is the current return path of your filament... your antenna...
Off center Fd4 antennas are probably beter...
73´s ON5MZ
What is the best CMC Choke to protect a SDRplay RSPdx? I have been told to use the DXE-RG-5000HD from DX Engineering, But looking at the specs. It states its for 500kHz to 150MHz but the RSPdx will cover 1kHZ to 2GHz. Is this still my best choice or is there something out there that will cover more spectrum?
Can you use a yagi 2.4ghz 25dbi antenna for uhf ? And if so what do i need to set it up
Mike.... have you ever seen a low pass filter that is supposed to cover all bands in one unit? I have a Drake TV-3300-LP. It says it is good for 1k watts max below 30mhz, and 80db atten above 41mhz. 52 ohms. Thoughts on this one???
This filter is for stopping RFI to Television reception. It Passes all HF ham frequencies below 30Mhz and severely attenuates those above 30Mhz
so i dont have any issues in my shack, or in my home... is this something i should run anyway??? @@andrewwilliss6500
I like picking up the wiggles! 73!
Good afternoon Mike, a ground rod with your SO 239 connectors grounded will help with overall noise. Dave Kasler has a great video on this problem.
Always trust a guy willing to say, “I don’t know.”
I don't know about that lol!
those are NOT CHOKES.
a Choke us defined as a very high reactance to be an OPEN CIRCUIT to RF.
Those cores are toroids with ONE TURN of very large gauge wire, very little reactance.
73
Us "nerds" look at that "stuff" so that A. We purchase the product that will meet our requirements. B. We aren't disappointed with the product when we use it, unless it doesn't meet published specifications. C. We don't go on social media asking questions that we can find the answers to ourselves. Not offended, just sayin'. Countless times, we all see questions that could be answered by doing a simple search, reading a spec sheet or, heaven forbid, read the manual! Sorry for the rant, it's a pet peeve of mine. 😊
So nerds outside of the U.S. don't look at that stuff? Interesting...
@@hamradiotube Damn autocorrect! 😵💫
@@thebnbaldwin Lol, get's you every time!
The Beatles suck
I know you need some fresh material for your next mean comments video
Sassy comment factory. NICE.
Yeah seriously. Reminds me of what us prepubescent teen boys said when the Beatles first appeared. I am that old. @@jamess1787
Do you actually have a Ham Radio License ?
How do you Not Know this most fundamental information ?
If your transmission interferes with any device, it means you are operating out of spec', illegally even.
But I guess you blame the other equipment, and its never your fault...
I actually have a license to do that. An EXTRA CLASS license! Oooohhhh.
@hamradiotube
To do what ! Be ignorant !
Ignorance is bliss they say, but I guess you'd be an expert on that also...
why not share your knowledge on the subject instead of your vitriol? I have an FT-991a (100W) & a Comet CHA-250HD vertical antenna and was wondering if i should put an LDG 1:1 at the feed point as the antenna is mounted on a 24 foot metal conduit next to my house and have heard so many opinions on the subject that my head is spinning. I ask because i have electrical wires about 30 feet away, not too far from the antenna and my radio is adjacent to the wall where my thermo-pump is (on the other side of the wall)... so be nice and do share what you know, if you do know. 73
@joearcuri3377
Hi Joe, I'm happy you asked.
I went to school and learned to read books. Then, I went to a big school, and learned to read big books.
Then, with that learning and knowledge, I made all kinds of electric things.
So read a book Joe, you'll be glad that you did.
I can't diagnose your issues just from your description.
You are the best tech / engineer to fix your issues.
@@snakezdewiggle6084 You're a real people person, aren't you? I'm almost sorry i asked, but couldn't help it, you seemed so nice. I was genuinely interested in picking your brain on the matter to see what you could share with a brother looking for some insight, and the community at large. What could've easily been a friendly exchange and an off the wall opinion on the matter, being that you read books and made things, you chose sarcasm and arrogance instead... Thanks for the advise snake, I hope you have a great day.