DIY RF Probe: cheap, quick, effective. Clamp-on antenna current/CMC meter.

[@DrHWO]

I made one a year ago using a 1950's milli ammeter which I used to measure the efficiency (or in those days, the inefficiency) of my home-brewed chokes. Its a useful piece of kit which I still use to this day. My Elmer used it as a teaching aid to get some concepts into my ageing brain, the XYL uses it it to encourage me to get off the greyline and the daughter uses it as a doorstop.

[@martinblain6200]

I will have a go at making a smaller version. thank you.

[@DL1GKC]

Dear Linas. Thank you very much for this again great video. Your content is so informative and practical. You show a lot of ham spirit when you share all your knowledge with us. I really enjoy your videos and have repeated a lot of your projects successfully. The next one will be a capacity hat for my vertical whip. Your videos are inspiring. Best 73 from Chris DL1GKC

[@Linas_LY2H]

Thanks a lot Chris! Sharing of our experiences among us hams is a second nature of Ham Radio, I think.73! HNY! Linas LY2H

[@kariolavi]

Thanks Linas! You have great and informative videos. The RF Probe should belong to every ham´s tool box. 73 and Merry X-mas de Kari OH2BCY

[@Linas_LY2H]

Thanks Kari! Merry X-mas and HNY! 73! Linas LY2H

[@kao354]

Linas, thank you for the video! This field meter is useful and simple tool.

[@vaamorais]

Great video. I am new to the hobby and still learning what some components do. Thanks. for sharing

[@2e0txe]

Linas! THANKYOU so much for making this video! Much respect, have a fantastic Christmas my friend!

[@Linas_LY2H]

Merry Xmas to you too OM!

[@dovpauzner5093]

Thanks for video !

[@K6TJO]

this is very cool. thanks for sharing this info!

[@dxdoctr1]

Thank you for the video. I'm not much of a builder. Do you know anything about the MFJ-854 meter? And, are there videos about how to find common mode current?

[@Linas_LY2H]

Hello, thanks for the comment! The MFJ-854 looks nice, except the price :) I don’t have one, so I can tell nothing about its work or the schematic diagram and design. If it’s based on the same one-diode-detector principal, there is nothing in it not to work :). Regarding the CMC detection, I’m afraid I don’t have a specific video on this issue. Search in the KZbin search engine should produce some certain amount of videos on the topic. Normally, if you have a CMC problem, you feel it immediately. Erratic behaviour of your radio, computer, CW keyer, burning feeling on your finger (at higher power levels) touching metal parts of the transceiver, microphone etc. Simple probs like the one in my video help to quickly detect common mode current on the antenna cable. HTH, 73! Linas LY2H

[@dxdoctr1]

@@Linas_LY2H Hi Linas. The common mode current shows up when I operate 20 meters. The symptom is USB COM ports dropping out. The MFJ meter picked up the CMC on the coax from that antenna and also on my earphone cord. Commercial choke (not from MFJ), to be installed at the antenna, is in the mail. 73 de Peter, AE1T

[@Linas_LY2H]

@@dxdoctr1 Hi Peter, sorry to hear about CMC attacking you , but good news is you have means to detect and fight it now! The RF choke at the transceiver's antenna connector will certainly help, at some extent, at least. It could be that to effectively eliminate the CMC from your computer USB cable you need to put some (3-6) clamp-on ferrites on each end of the USB cable, or wind as many turns as it can take around the toroid ferrite of FT-43 material size 140 or bigger at the computer side. Probably it would also be a good idea to investigate your antenna and try to understand why and where does the CMC come from and try to eliminate the cause, not only the consequences. Good luck and have no CMC! 73! Linas LY2H

[@fotografm]

I am going to build on of those tomorrow. Where did you get that huge snap on ferrite from ?

[@Linas_LY2H]

@@fotografm Hello, congratulations on your decision! My snap-on ferrite came from my junk-box and I most probably bought it at some ham -event :) But it is a standard snap-on ferrite and should be easily available at most internet trade platforms. HTH, have fun building! 73! Linas LY2H

[@samgrieg]

Thank you Linas for making this video. Wonderful channel to follow. I think, an old CB rf strength meter could be modified to measure common mode current by replacing its antenna with a toroid transformer?

[@Linas_LY2H]

Thanks Sam! Unfortunately, I failed to find such an old meter in my junk-box :) It would be just great if you make a mod to an old CB RF field meter and let us know! I think it should be possible, in one way or the other. Merry X'mas ! 73! Linas LY2H

[@yowsa52]

@@Linas_LY2H I have an old Radio Shack CB RF field meter., Im going to check it out.

[@wojciechb7896]

Hi good man;) When measuring, is the knob (potentiometer) set to 0? How to possibly correctly set? That's what I built from your project :) With a 10K potentiometer and a 100 uA ammeter. Regards Wojtek SP9DLK

[@Linas_LY2H]

Dzienki Wojtek! I'm so glad you took my idea for your own project! As it comes to the potentiometer, well, it depends on the meter you use and the strength of the RFcurrent you measure. In no way this RF probe is a precise measuring instrument, it's just an instrument to detect the RF current and get the orientational meaning of this current. But if you wish, you can do kinda' "calibration", like applying the probe to , for example, an antenna wire at the max current point, put some 5W into the antenna and adjust the potentiometer to the full scale on the meter. Then put 2.5W, then 1W into the antenna and notice the meter indications, and here you have a more or less meaningfull meter values! If you clamp this 5W calibrated meter onto the cable shield and see the needle at say 1W level, you will know that you lose ~1W of your transmitted power to the common mode current. Being creative , you can make many more different experiments! Good luck! 73! Linas LY2H

[@wojciechb7896]

@@Linas_LY2H Thank you very much :) Good job Regards and see you on the bands;) Pozdrawiam ;) 73

[@K6TJO]

Can you comment on the exact ferrite mix recommend (and perhaps part numbers for all the components from Mouser or some other supplier?) for this design?

[@Linas_LY2H]

Hi, thanks for showing interest in this design! I was ordering absolutely nothing from Mouser ( or anyone else, actually :)) for this simple project, everything came out of my junk-box. It is really does not matter so much the make or the size of a resistor, or a capacitor, the values are also orientational. As it comes to the ferrite clamp-on bead, it is only clear this is a high-permeability ferrite. As these ferrites are marketed as clamp-on filter beads, the impedance at a certain frequency specs is put in the first place in most data sheets. The metal oxide ( most often, I think, manganese zinc or nickel zinc) material is normally, the same type as in ferrite rings - 31, 43, 46, 61. As everything else, the type of the ferrite snap-it core is not so terribly important for this specific project, as it is always possible, and desirable to make some adjustment in turns of the transformer secondary winding. So, nothing being critical at all, you should easily select your favourite or available components at Mouser's or anywhere else, I hope. 73! HNY! Linas LY2H

[@crazyham]

Excellent. Can you tell me if this design varies a lot with differing frequencies ? Does it have similar sensitivity at 7 MHz as with 146 MHz ? I am pondering a design to cover 1.5 MHz to 150 MHz & Would like to know your experience with frequency response . Thanks for a wonderful video my Friend. 73 de VK3VKe ⚡🙏⚡ Just became a new Sub too ⚡🙏⚡

[@Linas_LY2H]

Thanks for watching and subscribing! I'm glad the video was of use for you. The device is a RF Probe, not the Meter :) This means, it can only indicates the presence of RF in the wide range of frequencies but it is not a precise meter which you could calibrate under different sensitivity levels :). It is surely possible though, to put marks on the micrometer's scale corresponding to the certain power levels after measuring the known power levels at known frequencies. It was not my goal though, as I mostly use it to detect presence of the Common mode current on the cable. As it is seen in the video, the probe easily detects RF presence from HF well into above 400MHz. The sensitivity is easily adjustable by rotating the variable resistor. The margins are very large for adjustable sensitivity in this way. HTH , 73! Linas LY2H

[@crazyham]

@@Linas_LY2H Excellent my Friend and ThankYou so Much for your speedy and accurate reply. One I am working on at the moment has a noticeable difference in sensitivity across the bands. When I have low Resistance on the POT it will show even small currents at as low 100 KHz but I noticed with my build that it was much more sensitive from 3MHz upwards. I hope and plan to upload a video on my own design and hopefully you will find it beneficial too. I am yet to proof, but I think I have came up with a more sensitive version with a more personal schematic and coil design. I Love what you are doing & Love that Hams continue to Share and Explore .. 73 OM, de VK3VKe ⚡🙏⚡

[@Linas_LY2H]

@@crazyham Excellent! Looking fwd to your own design! 73! Linas LY2H

[@crazyham]

@@Linas_LY2H Thank You My Friend. ⚡🙏⚡

[@ardilla8651]

Good videos and FB Channel. Suscribed. 73 EA3BV

[@rodw7zrc22]

Thank you for this reference ! 73, Rod/w7zrc