Test your feedline for common mode noise and shorts
HTML-код
- Опубликовано: 24 ноя 2019
- Test your feedline for common mode noise and shorts
5 PCB's for about $22 in about a week: www.pcbway.com
Yes!! I now have merch: teespring.com/stores/learnele... Electronics themed T-Shirts!
HEY YOU ABOUT TO POST SOMETHING STUPID:
Yes, I know my hands are large/fat. It's because of a heart condition I suffer from called Congestive Heart Failure. Here's a link to some information about CHF: cle.clinic/2TdS2Ux
One of the symptoms is that is causes fluid retention, mostly in the hands, feet/ankles, and face.
It will kill me one day. I'm doing ok right now, but someday...
--------------------------------------------------------------------------------------------------------------------
If you are shopping for electronic components, test gear or consumables please consider visiting my Amazon shop @ amazon.com/shop/learnelectronics
Please check out www.patreon.com/learnelectronics and pledge a dollar if you can. It will go a long way to keeping the channel alive. It costs a bit of money to buy all the items and produce these videos. You help is appreciated.
---------------------------------------------------------------------------------------------------------------------
Or....if you'd like to send a one-time donation you can use this link: paypal.me/learnelectronics
----------------------------------------------------------------------------------------------------------------------
Here is all the gear I currently use:
Oscilloscope 1: Hantek DSO4102C amzn.to/35cVK71
Oscilloscope 2: Siglent SDS1202X-E amzn.to/31Kk1yH
Power Supply 1: TekPower TP3005N amzn.to/2TeQnxI
Power Supply 2: RUIDENG DP50V5A amzn.to/2sNicSe
Signal Generator: JS2800 ban.ggood.vip/d9vk
DMM1: Owon18B amzn.to/2SbIGLs
DMM2: Aneng 8008 amzn.to/2sNQncI
DMM3: Aneng 8009 amzn.to/2S5qeEp
DMM4: Uni-T UT801 amzn.to/2S89SuL
Soldering Station1: Zeny (Yihua)862D+ amzn.to/2S49z4e
Soldering Station2: KSGR T12 amzn.to/2Wk7Dn9
Light Meter Smart Sensor AS803 amzn.to/2B2gyRg 
Наука
The male plug is a PL-259, the female socket is the SO-239. The error doesn't take away from your great lecture.
The ugly balun only gives RF choking over a very narrow bandwidth and in some cases can actually increase common mode. Go with coax coiled thru a FT240 ferrite toroid core option
The connector is incorrectly referred to as an SO-239. The correct description is PL-259. The antenna socket mounted on the rear panel of radio is an SO-239.
I never thought of testing with just the center conductor without the shield. Such a simple but effective idea to check for common mode noise. Now I need to figure out how to apply this technique to a BNC or SMA connector. Thanks Paul, another great and informative video!
C'mon....
SO239 is on the back of the radio.
PL259 is on the end of the feed line (coax)..
Dude - that was one of the most valuable and clearly explained lessons I've heard. So many people too deep into the reasons behind the problems that they don't bother providing simple step by step processes like you did. You just got a new follower! Thank you!
+1 !!!
Pretty interesting, dude! Thanks for all the tips! 😃
Hi Nick here from Portugal, love your videos, thanks man
Half of my dipole antenna is connected to the shield so it makes sense to me that the signal strength along with noise would increase with the shield connected. Repeat the same test on a busy frequency and see if their signal strength also increases.
Useful information. Thank-you.
thank you for this material
Nice. I'll try that when I get home. I thought one should short the center conductor to ground when checking internal amplifier noise, else you might still pick up noise from the surrounding environment. Thanks Paul and Have a Happy Thanksgiving.
Very useful stuff!
Good video.
Just a minor nit, but since you named the channel learnelectronics, you want it correct.
PL stands for plug and SO stands for socket.
SO-239 Is a SOcket. That is the antenna socket on you radio.
PL-259 is the PLug that goes into your SO-239.
If you buy the SO-239to put on your coax, you will get the wrong part.
Thank you! Im gonna do it.
Thanks,… very helpful my friend
Thankyou very much for video I am also getting QRM S-9
That's a PL259.
Great video Paul, but shouldn't you be using a 50 ohm dummy load for the receiver-without-coax test? I don't know what type of coax ur using but I found by using a quality coax like LM 400 (double shielded) coax with the chokes placed at the antenna feed point will help a lot. Also, using the receiver's internal or an external (audio) active noise filter helps with that atmospheric noise. And lastly, make sure you stay alive long enough for the next solar cycle max, at which time the wanted signals will far exceed your QRN level.
Have a relaxing Happy Thanksgiving day.
I love Mexican radio! Thanks for the video
Nice tricks to get rid of common mode noise, I am not playing with a Ham but it’s always nice to know ways to cut down on noise when you has a signal trying to get through. If you ever have problems getting a good signal through a cheap 10’ usb cord ferrites may help with that too. Great video Paul.
10-foot ferrites?
Differential mode current doesn't travel on the center pin alone. The is an equal and opposite amount of current on the *inside* of the shield. Due to the skin effect, the inside and outside surfaces of the shield along the coax can be seen a two theoretical conductors. Any current on the *outside* of the shield will be travelling in the same direction as the center pin and is considered common mode.
Not really sure what happens when the shield reaches the chassis of the radio. But it's the equal and opposite current between the center conductor and inside surface of the braid that cancel each other out and prevent the feed line from becoming part of the antenna system.
Great video. I was reading about this test on Palomar, but the video really helped! Palomar's instructions said to "remove the coax connector". That made me think that cutting off the connector was necessary, which I didn't feel like doing with my brand new pricey ABR coax. Thanks so much for simplifying this!
Glad it helped!
Thumbs up, and another test from long ago:
Short out your antenna input and turn up the AUDIO gain, and turn off the squelch. If you hear noise then, the audio circuits in the radio are noisy, and may need some work. Bang lightly on the side of the radio, and listen for harmonics too.
Additionally, you can install a 50 ohm terminator into the antenna connector. If you can still receive signals, even broadcast stations, your radio may be lacking sufficient shielding or grounding.
73
For sure guys/gals this works. I made an ugly balun years ago, but it is better suited for being outdoors as close as possible to the antenna feed point. It’s a little large for in the shack and hard to get real close as possible to the SO-239 antenna connector on the back of your rig where it needs to be. Because the closer to the radio, the better. For in the shack you can make your own common mode choke that has a much smaller footprint. A 2 inch ferrite ring and about 6ft. (or even a little less) of RG8 coax with the PL-259 connectors already on it. Around 10-12 loops around and through the ferrite ring (many examples here on youtube). Make sure your PL-259’s don’t end up next to each other (again watch youtube tutorials on this). Make one side have only about 2 or 3 inches of coax hanging (this will directly connect to the SO-239 on the radio) and the rest will end up being about a foot left over after the windings. You’ll need a barrel connector to connect your new choke to the regular coax that goes out to your antenna. Like he says, you can mix/match or use same types of chokes in series with barrel connectors. Yes the presenter incorrectly calls the SO-239 (socket) on the back of his transceiver a PL-259 (plug) numerous times, but I think we all know what he meant. We’ve all made the same mistake at one time or another. Not a big deal. Installing a choke(s) and grounding your coax shield is the good 411 here.
Very helpful
At or around 5:28 where you state that when you connect the coax shield back to the radio, if the static or noise stops you know your antenna is shorted-out, there is another side to this. I can agree that if the receiver goes silent, then a short somewhere in the antenna system may be the case but if you are tuned to a weak signal and you hear all the static/noise with the shield disconnected and then when you connect the shield back to the radio, the S meter should actually show a lower level and the static/noise will be reduced and you will actually hear weak signals much better - this is assuming your antenna system is in good order. Without the coax shield in good order and connected properly at both ends, and any splices along the coax, the coax becomes part of the receiving and radiating antenna system and you don't want that. To make it clear, the antenna "system" includes everything from the radio to and including the actual antenna itself. The "antenna" is the only part that should be receiving and radiating signals. A lot of QRM was caused years ago by most all of us ham radio operators simply connecting our coax directly to dipoles without a matching device located at the antenna - up in the air within a few inches of the physical antenna itself. Of course everything was analog back then especially TV and it was easy to cause trouble to the neighbors, including the telephone, making the garage door fly up and down, getting on the stereo and so much more. Digital technology is our friend nowadays and most of us make much better antenna "systems" today than we did 60 years ago. Good quality coax (for example, LMR-400) with a true balun connected right at the antenna for any balanced antenna, like a dipole, or a hexbeam, the yagi is an exception with a gamma match, is the best way to do it. 73 WA4QGA
And learn how to solder you PL-259's onto the coax for a good solid electrical and mechanic connection instead of crimping and using heat shrink to hold it on. And I have never seen a good shield connection on the cables with the molded rubber boot on the connector - it's basically just stuck it the back and the rubber injected around it to hold it ! And wondering about the fact that you unscrewed one coax but then used another for the demo ?
Thank You
I know It might sound like a bit of silly advice please disconnect your microphone from the radio before you unplug the pl259 plug from the back of your radio. If you accidentally key up without an antenna connection you know what will happen, you will damage your pa stage it’s better to be safe than sorry.
i think u forgot all about the ADC , anyways i still enjoy your videos , thanks man
Thanks!
I learned a lot. I live in a condo which has a LOT of noise . This is where I will start. Thank you for your time and help. N4KBM
@ 2:50, not all cables have the ability to completely unscrew the barrel, notably premade molded cables.
Where is the other half of the video???? This good video would have been GREAT had you shown us you installing the different RFI suppressors and the differance they made.
Thanks
Very cool tip cool.
I'd love to be able to see what the RF noise level was 500 years ago. Where I live there's almost always a high noise level.
Or 10 million years ago
Good video, but I have some questions:
1) Shouldn't you be measuring the no-antenna case with a 50 ohm load at the input?
2) The common mode noise explanation at 4:30 doesn't seem right. The differential return from your feed line should be on the inside of the shield. Because of skin effect, this is actually a separate conductor than the outside of the shield. If 100% of the return isn't on the inside of the shield, some of the return will be via the ground, which indicates a common mode component in your signal. When you don't hook up the shield, 100% of the signal is forced to return via the ground of course.
As an aside, I watch and enjoy and give thumbs up to nearly all of your videos, but I don't remember you testing your antenna's VSWR using the NanoVNA. Apologies in advance if you've already made this video and I've forgotten about it...
Well, I agree, lots of problems with these methods. If he has noise in the room, the noise would go way up with just the pin of the coax plugged in. The method I would use would be one test without a common mode 1 to 1 well made common mode choke. 2 using that choke, what do you get. All of the common mode noise would go away. Most who use these chokes say nearly all systems have this problem. It would be cool to switch the common mode completely in and out of the circuit with a switch or relay, That would be a great demonstration.
Center coming in, shield out, outside of insulation is rf comes back in.
"Ground your feedline." How would you do that on an upper storey?
Wished you would show before and after video...
At the end of step 3 you reminded me of this old Russian anecdote...
-- "Excuse me, can you give me directions to the library, please?"
-- "Sure. Go down this street for 200 meters, turn right; go about 300 meters and you will see a bus stop. Take bus number 46; the 7th stop is yours; cross the street and walk towards the park; when you see a church, turn left. Soon you will see a metro station; take Red Line to station Mir, get out, turn right, walk for a few minutes, you will see a huge 3-story building on left. That building is NOT a library!!! Turn around, go straight for 2 blocks,..........."))
what does it mean if as you showed, the noise is on the center conductor and not common mode? My noise floor is usually between S6 and S8 even with a Palomar engineers common mode feedline toroid. thank you much!
Very informative, but one question, I was dealing with a radio that wasn't receiving a signal all of a sudden. If I only connect the center of the coax, I could hear a signal in the speaker, connect the outer shield, the signal went away, any ideas? Would be interested to know your thoughts. Thanks.
sounds like a short in your antenna system
I have an issue in my neighborhood somewhere I get 9db of noise and I believe its on a timer I notice it when it gets dark and once sunrise hits its gone The closest lighting is at least 150ft from me . Any suggestions to decrease my noise level
But you have a ground wire. So there is still potential noise coming not from the antenna!
Balanced antenna's like a dipole direct fed with coax and no balun are notorious for picking up common mode noise. Coax cable is an unbalanced feedline and loops and dipoles are balanced antennas. Although many hams hate baluns, if you don't want your coax radiating instead of the antenna, a proper 1:1balun at the feed point of a dipole ensures that the coax won't radiate and the antenna will. You cannot properly feed a balanced antenna like a loop or a dipole with coax and no balun, the coax WILL radiate RF before it reaches the antenna. Many hams insist on doing it that way because "It always worked for them" but that doesn't mean it's the right way.
By unscrewing the barrel of the " PL259 " you are causing the coax to behave as an antenna , So if this coax runs past , Lets say a switchmode power supply from say a laptop it will pick up the radiated hash generated by this power supply , This isnt an ideal way to find noise on your coax.
This is a standard method taught to RF engineers for the last 30 years. But if you dont like it, by no means should you follow my instructions.
@@learnelectronics in your defence this technique works very well. It may not be perfect under all conditions but it definitely works.
Thank you for the information! I am new and will be getting my first HF radio soon! This will help me.
I enjoyed your clip very much , but for an ugly balun what diameter does it needs to be? 👍
He indicated 4 inches.
what if you have a lot of noise when you disconnect the antenna?
What if your common mode noise is generated by your own tranmitter during transmitting. Other than it biting you as an rf shock.
Oh ya ,…. Watching from Kentucky “The Bluegrass State “. !
What would have completed this video is to connect all those suggestions and connect them to your transceiver and then show the "dramatic" reduction of the noise! if any!
Ty
So when i get to step 3, I re screw the threaded barrel on my noise level drops from S3 to S1 ? What does this indicate ?
It indicates that your QTH is great for ham radio!
What is the model of that Palomar box thingy?
surely pl259?
so what does it mean if the noise goes down when i connect the ground but only on higher bands, on lower bands 20 and below the noise stays the same?
You probably don't have enough inductance on your common mode choke, see my other post. I have played a LOT with common mode chokes.
This made a lot of sense - I just couldn't make heads or tails of the technical papers. Now to find a Mexican radio station! ;) 73
Plug = PL259
Socket = SO239
i get lost myself with 39 n 59 lol
@@XPFTP The clue is hidden in the name ;-)
PL (ug) 259
SO (cket) 239
@@nlo114 ya know dumbazz me lol sometimes the simplest things are over looked lol .. ty for in .. i learned me sumffin new.. but ill probley still forget lol hahahhaha
Until, you actually put Power to the antenna you have no idea what the CMC is, what you just showed is the shield acting as a receive antenna. That is only a fraction of what you are hearing.
What would you if you here static when your furnace starts
I would go back to school and learn to write proper English.... 🥴
Check to wiring and condition of the voltage transformer of the furnace.
Thanks for that video. If you’re looking for more video ideas, how about one on grounding? My “shack” is on the 2nd floor and I’m puzzling a bit on how to properly ground my rig. I have an 8 ft rod in my garage, but that’s as far as i have progressed.
Do a research on "artificial grounding systems". Take a look at the MFJ-931 from MFJ Electronics.
@@MrVosh-nj2lc Thanks, that's interesting. I had never heard of such a thing.
@@karllaun2427 You're welcome, best of luck & 73's
what if it gets quite a bit louder when you screw the connector on?
Then you have common current noise
@@learnelectronics that is not necessarily true, if you have an effective common mode choke you will receive very little at all with just the centre pin connected..
Yeah.. "Who doesn't love a little Mexican Radio"... right in the middle of 40 meters... 73!
And now you have Cuban jamming all OVER 40 meters ...
How do you have common mode noise on receive ?
It can massively increase noise levels in some situations. and it does exist.
Did you ever address your s8-s9 noise?
U just help me out thanks
Short out the Receiver input insuring noise is not internal to the receiver. Injecting a known Signal in the beginning of the coax (Antenna End ) thru the path provides a base line on your line noise levels. Line Loss. If available a Freq Selective Volt meter Terminated in 50 Ohms does this job most well.
A good video but you do have tons of common mode noise, if you use an EFFECTIVE common mode choke the rig will barely receive anything with just the centre conductor attached. If you doubt me try a short patch lead passing through an FT240-31 perhaps 10 turns. The "UGLY BALUN" often makes things worse, and the ferrites need more turns, they should also be the right mix ferrite.
You mean pl259. So, how much do you know?
I should also ground my rigs , correct? 😎
Now we know...
Thanks for the nice movie 73s LB7VI
You switched connectors. The first one was molded.
yes, because it didnt unscrew
Something that has been slowly rising to the top of my personal "pet peeve" list is what people have been calling the UHF coax connectors lately. I understand getting confused in the nervousness of the recording too.
The connector on your coax is a PL-259 plug (the center pin is a male "plug"). The mating chassis connector is an S0-239 (the center pin is a female "socket").
I am not faulting your general content and you definitely are not the only or first one to use incorrect nomenclature in their videos.
One other technical point, the item you described making at the end is a coaxial choke and while the PVC can make it look neater, just coiling the coax up for 5 or more turns and securing with tape or ties will do, but these do more to help with transmitting issues. BALUN indicates a device to convert BALanced to UNbalanced which this configuration does not do.
Good luck 73 & keep up the work WB8FEQ since 1969
Pl259 connected to radio
I would super-emphasise putting more than one turn of coax through the ferrite clamps, rather than just extra clamps. To see why, check out 'The Effectiveness of Ferrites' on qrm.guru/the-effectiveness-of-ferrites/
Hey bro great video. Im having super issues with my CB install in my Jeep Wrangler Running a Cobra 29 mounted above my rear view mirror, antenna on the back steel bumper on an antenna mount where I used a flat braided ground line bolted to the frame of the jeep to the antenna mount. connections both to the antenna mount and frame of jeep were cleared of any paint - so its direct contact to bare metal. When I turn on the cb im getting great signal receiving with no issues. the second i try to use the mic and key in - my dash goes crazy lighting up everything, making the wipers go off and tachometer bounce around. Do you think this is a common mode issue? im running out of things to try lol any help would be great bro
Have you connected the radio directly to the battery, on both wires ?
@@howardhiggins9641 yes both wires are connected directly to the battery. Im really running out of options lol
@@johnnyalonso You might also try a coax cable with better shielding.. Are you getting a good VSWR ?
I have read other posts that SOME jeeps, in particular, have mobile radio problems. Have you asked Jeep about service bulletins on the issue ?
@@howardhiggins9641 thanks for the reply. I'm going to have to swap out my coax for one wirh better shielding I just don't know which ones have a better shield lol ant recommendations? Ans yes I've called a couple jeep after market shops and both have only come across this problem with newer jeeps. If you know of any good shielded coax or if there's something I can wrap the coax with let me know. Thanks man
@@johnnyalonso Whatever you do, go with a BRAND NAME coax, not some junk off Amazon.
If we absolutely knew this was the problem, I'd say to use RG-400, which is a double shielded construction.
All coax is sold by the foot, and the best price you'll probably find type for this is $3.75/foot.
A heavier coax would be difficult to install. You should read up on installing coax before you spend any money. They all have a different minimum bend radius' If possible, and you can still route it without problems, I suggest you buy the cable precut (with only a slight amount, say 1/2 foot ) of extra slack, with the connectors professionally installed..
Good luck.
And uh, who doesn't like a little Mexican radio?...
Check what you said again,,,,,,,SO 239 is not a PL259 Which is what you reversed iI saying...
BULL SHIT - WITHOUT THE SHIELD YOU HAVE A LONG WIRE ANTENNA.
No. Wrong. Try again.
Show your work.
Even a long wire needs a ground
wanna trade a 756p3 for the 7300? hahhahaha oooo to bad u didnt have one.. so i could learn how to do the backlite the rite way ..
It would have been nice if you would have connected all those solutions to your radio and showed how it worked in reducing the noise. A before and after thing.
5:15 i dont think your right about having a short if static goes away after connecting shield. Static Noise is Depending on your squelch setting after full connection. Correct me if wrong.
Just put a short verticle up as far from noise sources as poss. running the co-ax along the ground, with earth stakes at bottom of verticle. But dont run wires from them back under verticle. Experiment with dissconnecting/re-connecting earth to back of rig. Ugly baluns work well, also reducing SWR on Xmit!
I see this was a year ago. This was actually a lot of wrong information. I hope you realized by now that you had a ton of RFI and the ferrites are meant to help RFI and not common mode noise. You could have also mentioned shortening your feed line, using a 1:1 choke and grounding the antenna as additional ways to stop common mode noise.
No, this is wrong. The use of ferrites is to choke or impede the flow of common mode current. For instance, on the outside of the shield of your coaxial feed line. Having this CMC makes your station susceptible to receiving RFI, and in reverse when you transmit, you're more likely to cause RFI.
So I don't know what you're talking about. This is concerning considering you're trying to correct this individual when another may read it and buy into your story.
I see this was two years ago but.......
I'm sorry but this is a "faulty" test . Basically you plugged the inner of the coax so what should be 50 Ohm now is 450 Ohm wich is nothing less and nothing more than a "long wire" but the un un 9:1 AND not tuned at all. Of course your receiver gets kinda saturated because the antenna, wich act as a random wire, is receiving everything . This won't tell you anything at all : you get exactly the same with ALL aerials and theyr coax if yo plug the inner by every receiver of your choice . You only have to test putting a common mode 1:1 rf choke on the antenna side, or back of the radio or both . There's no magic and no other way . Oh and i'm sorry but you have LOADS of noise due to the common mode current...it's more than clear just listening the "sound" of the noise . Last but not least you should use the Ipo or a attenuator when listening on low bands : this makes the receiver front end more happy (but you may did that because the video and to show a reasonable signal) .