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  • Опубліковано 12 січ 2025

КОМЕНТАРІ • 264

  • @hankhamner3671
    @hankhamner3671 4 роки тому +14

    Hi Alan,
    I used your approach and it works so long as the measured impedance is close to 50 ohms. However, I tried something a little simpler and compared my results to both two separate calibrated nanoVNAs and my calibrated RigExpert AA55 and my results came out within 5% of these analyzers. The two nanoVNA's were within 2% of each other and the RigExpert was a little further off.
    My circuit is simply a 1% 220 ohm 1/4 watt carbon resistor connected in series to a function generator and an HF antenna. A 200 MHz digital scope with phase measuring capability set up for 10X probing on channel 1 and 2 was used. No 50 ohm terminations were used or needed because all I was interested in was relative RMS voltage at the top and bottom of the 220 ohm resistor referenced to ground and the phase difference.
    I plugged the two measured voltages at 7.213MHz and 14.250MHz along with the phase into an Excel spreadsheet to calculate the load impedance, return loss, VSWR, both rectangular and polar coordinates and reflection coefficient. I used the scope's averaging to get the voltage to settle on the sine waves. The results I got were within 2% or better of the nanoVNAs and within 5% of the AA55 RigExpert antenna analyzer.
    I have not tested large impedances relative to the 220 ohm resistor but I suspect if the impedance is between .1 to 10 times the reference resistor (22 ohms to 2200 ohms) I should be reasonably accurate. I would appreciate your opinion on my setup and any issues you see. I may just have been lucky to get close measurements.
    I got the idea to try this simpler approach from Kenneth Kuhn's article titled "A Simple Circuit for Measuring Complex Impedance" "www.kennethkuhn.com/electronics/impedance_measurement.pdf"
    Thanks and I really appreciate you taking your valuable time to teach all of us electronics.
    Hank Hamner
    K5HHQ

    • @achernarscardozo69
      @achernarscardozo69 2 роки тому

      Gracias por responder. Creo que los valores que encuentras son más que suficientes para una estación de aficionado sobretodo cuando estos se encuentran en las proximidades de los standard y como tú dices además y es que finalmente el transmisor “ve” todo lo que haya más allá del conector. Siempre me ha interesado la medición real de la impedancia de una antena de HF y esto no es muy práctico por la dificultad a un acceso directo a la misma o al diseño de un analizador de características muy especiales. Abrazo.

  • @OctavMandru
    @OctavMandru Рік тому +4

    Dear Alan, 9y later your lectures still provide a masterclass on RF and EE. It is great to see you juggling with numbers like that. Thank you Sir
    Regards from yo4ocm

  • @bain5872
    @bain5872 11 років тому +49

    You have an amazing ability to make one of the most complicated subjects into a very straight forward and most understandable presentation! I wish you had been my lab instructor back in the day! I sit in amazment at your soft and to the point teaching style with a hint of a very understanding attitude. Absolutely fabulous knowledge and teaching style! Kudos to you Sir....! I admire your vids.

    • @w2aew
      @w2aew  11 років тому +5

      I'm glad you liked it!

    • @wa9kzy326
      @wa9kzy326 5 років тому

      100% agree with your views.

    • @rusty1187
      @rusty1187 3 роки тому

      I agree! I have had maybe two good teachers in my life, and you, sir, would be the third.Easy to understand, and you don't talk down to us all like a certain lab channel that i watch.

  • @tomsmith3045
    @tomsmith3045 Рік тому +3

    Just finding this today. This is such a handy thing! Just a simple bridge circuit, but never thought to do it to tune a circuit. I'm going to have to build one of these. For weird bands where you don't have an analyzer, or for working with 75 ohm systems, it's a great trick to have up your sleeve.

  • @jgwimmer
    @jgwimmer 10 років тому +5

    I'm a software engineer, but started out working on my EE while I was in the Air Force, 21 years in the Comm business...you've given an absolutely fantastic instructional video. Easy to follow along, easy to understand, and outside of the math for some folks, a very easy to understand way to apply theory to real life. I applaud your efforts and hope you do many more instructional videos to help those who don't quite understand.

    • @w2aew
      @w2aew  10 років тому +3

      Thank you! I've got 187 videos and counting! I hope you enjoy the rest as much as this one.

  • @wa9kzy326
    @wa9kzy326 5 років тому +3

    For a few scraps of PCB, some connectors, and resistors, this is a brilliant method to "see" the workings of an antenna/transmission-line system. The advantage of the 'scope is it's very high voltage sensitivity-10 mV/div. It will work with a favorite of amateur operators--MFJ259B as a signal source. In spite of its limitations, it's worth a try. And voila, resonance and resistive match in one fell swoop. This is an excellent candidate to sell as a kit. Your level of practicality is amazing and a badly-needed adjunct to the amateur "rags" of today. Words of thanks are barely adequate.

  • @davidlong2691
    @davidlong2691 2 роки тому +2

    So cool! I just learned today that these bridges are the foundation for how the NanoVNA version 01's work - though the oscope is replaced by low sideband mixers and a 3-channel audio ADC.

  • @skyking6989
    @skyking6989 4 місяці тому +1

    Ham radio operator and currently studying Electrical Engineering. Ham Radio and electronics has always been a hobby. Now a career

  • @w2aew
    @w2aew  9 років тому +5

    to John Brown - Yes, this is not uncommon - and is one of the things that makes analyzer like the MFJ-259B difficult to use on low-band antennas sometimes. A bandpass filter can often help, but it all depends on the frequencies of the incoming (interfering) signals.

    • @gelubotezan3917
      @gelubotezan3917 9 років тому +1

      +w2aew I couldn't find John Brown's message so I just suppose he had problems trying to measure with his analyser into the lower HF bands.
      I use a VK5JST analyser and had problems with a MW Broadcast station about 25 km away. I just connected an 1:1 choke balun between the line and the analyser and I am able to steady measure in all bands. Measurements confirmed by trcvr working with the antenna as set up with the VK5 JST analyser

  • @suriyontm
    @suriyontm 11 років тому +3

    Thank you for all the awesome tutorials on transistors. You are the only one that really explains things very well and easy to understand. Keep up the great work!

  • @6345788
    @6345788 8 років тому +2

    Very nice demonstration with the visuals of impedance. I really think the use of the scope and tuner gives a great picture of antenna matching. Great teaching skills, my friend!

  • @MarceloMoraes
    @MarceloMoraes 10 років тому +5

    An excellent explanation on how to tune an HF antenna that I ever have seen. Congratulations! Great!

  • @AppliedScience
    @AppliedScience 11 років тому +7

    That's pretty cool! I've never seen a visual antenna tuner, but that makes a lot of sense. Good idea.

  • @JimSky
    @JimSky 10 років тому +6

    W2AEW you are beginning to seriously eat into my free time with these great videos. Tonight I was working on a bridge by k6bez for an arduino based antenna analyzer. I just felt like I could count on you to have a related topic. This was perfect. Thanks -kh6sky

    • @w2aew
      @w2aew  10 років тому

      Very good! I'll have to check out the Arduino project...

  • @kendeken2868
    @kendeken2868 10 років тому +1

    Much more information than a standard SWR meter -- good explanation.

  • @Digital-Sparks
    @Digital-Sparks 4 роки тому

    This is my kinda ham radio stuff, great video, and thanks for making it, I work on radios of all types, also a General Class operator and a industrial electrician, self taught electronics tech, and I LOVE this aspect of our hobby. There is nothing more satisfying than making your own antenna's and gadgets and gizmos and being able to say when asked, were did you get "XYZ" from..... I made it!
    Although I am a "maker" I love these type videos, and I hope that it inspires others to experiment in making things for their stations.

  • @dimitriapproved
    @dimitriapproved 4 роки тому

    Just built it and it works!. It was faster to build it than finding an antenna analyzer on a Sunday night !!!

  • @nicholasbantell2520
    @nicholasbantell2520 9 років тому

    I just finished building mine. It works rather well. Thanks for the all of the videos. I really appreciate all of the free education you pass along.

    • @w2aew
      @w2aew  9 років тому

      Nicholas Bantell Excellent! This is what I always hope to hear, that these videos have inspired people to build, test, experiment, learn, think, etc.

  • @MochaboyRC
    @MochaboyRC 11 років тому

    That was fantastic...Very concise and easy to follow. I make my own high frequency antennas (433, 1.2ghz, 2.4 and 5.8) and I use a DIY SWR meter, but this fills all the holes for the other measurements I was looking for. Very handy technique - thanks for documenting.

  • @robertw1871
    @robertw1871 6 років тому

    Little bit out of date finding this.... I can see a couple ways to make it more complex, but eliminate some of the other hard to control bits. A couple of opamp instrumentation buffers could drive the scope with low Z to eliminate all of the termination and coax impedances, you’d most likely have to layout a PCB to pull that off though. Using some board edge BNC and SMD components to further reduce parasitics, would be worth while I think. Might take advantage of the opamps to invert one of the outputs and shoot for a null rather than trying to match waves. Also a great time to use that old analog scope with its infinite bit technology as 8 bits of vertical resolution is a rather limiting factor for most ‘affordable’ DSOs. I’ve been kicking around ideas to do something like this and you provided me a starting point, or rather, near end point. Thanks for the great presentation.

  • @alfbaz5248
    @alfbaz5248 11 років тому

    Brilliant and thank you! Being a self taught hack you have given me one of those moments were several loose pieces of knowledge all come together in a wonderful symphony with regards to polar, rectangular and complex notation. If you do make a video about that subject, I for one, will be very greatful

  • @g0fvt
    @g0fvt 7 років тому +4

    I just stumbled across this video, I probably have already watched it. I understand the methodology etc but nevertheless it was fascinating and very well presented. Well done once again

  • @sasines
    @sasines 7 років тому +2

    You do an outstanding job with your videos! Very clear and easy to understand. I have subscribed and look forward to seeing your future videos as well as going back and viewing your earlier ones. Thanks very much for taking the time to do this.
    73, Alan W3AL

  • @DAVET38
    @DAVET38 11 років тому

    Another very good video Alan. As usual I enjoyed your circuit analysis. It is nice to see all the complex theory I learned in my electronics courses used in a practical context.

  • @patrickbouldinkm5l143
    @patrickbouldinkm5l143 9 років тому +2

    What an awesome video, content and generosity in sharing knowledge. This is the essence of amateur radio. Good job! - Patrick KM5L

  • @RichardKCollins
    @RichardKCollins 5 років тому

    If you take the digital data from the scope curves, you can find the best match statistically. I do not know if there are digitally controlled tuners, but that matching can be done to arbitrary precision by using all the data in the signal and letting it run for a while. The statistical fluctuations will be local changes in temperature, electric and magnetic fields, internal noise in the power. Then fields from power systems, electromagnetic manmade sources, and natural sources. I am trying to get down to levels where the gravitational field can be measured, and that means identifying and adjusting to all the noise sources mentioned above - in real time, or by recording everything and doing it after the fact. Gravitational detector arrays are growing rapidly, but every instrument needs to be checked carefully for electromagnetic noise of all kinds. Since electrons have mass that "noise" will include seismic and vibrational noise, and movements. However tiny the signals, they will usually be there. Being thorough helps. Recognizing that every "noise" is a signal of something happening somewhere helps. And every signal has a group that is working on it.
    Nice video. Thank you for explaining carefully and precisely. If you record the data and apply some basic regression you learned in school it will help make sense of what is happening in gravitational engineering these days.
    Richard Collins, The Internet Foundation

  • @PeterWalkerHP16c
    @PeterWalkerHP16c 9 років тому +1

    Great video. One of the best for this subject.
    This is my meat! You could use this idea not just for antennas but for for visualising filters etc. One could also use the inv and/or add functions on the scope to to aim for a max sine-wave or flat line. XY might also give some interesting results.
    With persistence, and a good CRO (scope), HP calculator, variable network filter and LTSpice et al and you can immerse yourself at a practical level till you really, really *_know_* this stuff.

  • @Afrotechmods
    @Afrotechmods 11 років тому +4

    Brilliant!

  • @MichaelLloyd
    @MichaelLloyd 7 років тому +3

    This was exactly what I was looking for. Thanks a bunch

  • @ernestb.2377
    @ernestb.2377 Рік тому

    Interesting exercises to follow along and to play with. I am not used to the XY-mode of a scope, but could that help some to read the phase shift more accurate on the scopes that do not have automated measurements? But very good to use these measurements and calculations to exercise the complex number calculations, and the compare with different measurement devices. But as the frequency goes up we have to take more and more care about the used components and the setup in general. Thanks !

  • @BalticLab
    @BalticLab 11 років тому

    As usual, pretty darn good. Even though I am familiar with most concepts of the electronics you are explaining, the way you present information gives me nice ideas for teaching others. And on top of that I love your little creations with big effect, like your probe holder for instance.

  • @jonathanblack1416
    @jonathanblack1416 Рік тому

    This is awesome, o only know very limited knowledge of electronics from my dad growing up, he was in the military for electronics and worked on radios and the original huge night vision scopes. He was stationed in Taiwan. I built quite a few things growing up like the lie detector and an guitar distortion box I still have today somewhere that I loved the best. I found you here looking how to get to find the exact frequency of antennas or more accurately for what in doing exactly is making copper coils as a necklace pendant that I’ve been working on for 7 years now daily and I’ve always been driven crazy trying to find certain frequencies that do certain things for healing and I’ve see miracles with them but I’m in the dark what frequency I’m making because the wavelength changes when I coil the wire into a custom coil I designed of my own that’s really amazing but I’m goin insane because I do t know what length to make them to compensate for the winding so it’s pretty maddening for me, then I heard someone out here talk about finding the frequency of an antenna with the oscilloscope and I didn’t think it was possible really but I’m seeing in my head it can be. I found a cheap used one near to me to get once I get my tires put on I can go get it. Is there an easy way to see the exact frequency of a copper coil that you know so I can see what in ending up with so I can find a compensation to get what I’m wanting to make in the end after winding it up?
    I need some sanity lol.
    I’ve been working bday and night on this for 7 yrs trying to solve this mystery without the tools or skills to see what I’m getting in the end. Just want I help people feel better easily and I’m getting Somwhere good with it finally just recently the hard way but I’d like to refine it to perfection this way.
    I’m good with doing the electronic work and can solder like a robot since I was 4 or 5. But my technical knowledge of the finer parts of it all is blah 😂. Was never good in school or math. That’s why I can’t believe I’m doing this for 7 yrs mile a mad man. It’s my wanting to help people not suffer that drives me to do what I’m the worst candidate to do it. I care probably way too much and want to find easy and safe ways to stop suffering for us all and not hide it. I’m doing a good job of that already now for 35 years and it all led me to invisible light colors bam dive got down how to make any thread of any color of invisible light for some years now by El wavelength and all I need to finish this off is to find what the coil is after winding it and then I can help people way better. I’ve seen literal miracles with this I created. If I can know exactly a frequency when it done I can cure anything by people just wearing a necklace tuned to cure just about anything. I do it underground to keep my life of you understand. M
    Any help will be helping not so much just me but mostly others really.
    I do it all for free as I believe it should be.
    It’s cost me at least a quarter million over the last 33 years curing people of just about anything you can imagine at my own cost. So now I’m broke but I keep going. I’m a bit crazy as you can tell 😂 m
    It takes crazy to do stuff like this.

  • @ronaldlijs
    @ronaldlijs 11 років тому

    Excellently explained as always Alan, thanks for sharing your knowledge in a way we can all understand clearly and easily! Regards, Ronald

  • @g0fvt
    @g0fvt 11 років тому

    Another excellent video, great to see it done from fundamentals and actually it seems to pretty well vindicate the MFJ as being a useful piece of test equipment, certainly at HF.

  • @fir3w4lk3r
    @fir3w4lk3r 11 років тому

    You used an instrument to tune the antenna. After that you use the number on the dials to design a equivalent circuit to hook before the antenna?

  • @dalesmith8666
    @dalesmith8666 Рік тому

    If memory serves me right, the AD8302 would be a perfect candidate to measure the phases of the voltages. Nice video.
    I use the HP4815a, and the HP4193a, but unfortunately affected by strong RF signals, from signals received on the antenna. I should try your concept, of course using none reactive glow bar resistor, I hope! LOL!.
    For those interested in more info, about the ad8302, see, Analog Dialogue 35-05 (2001)
    73's, Dale.

  • @markbell9742
    @markbell9742 11 років тому

    WOW; Knock My Socks Off. I am not a Ham guy but, I have built a couple antennas for radio astronomy (Jupiter lightening and Crab Nebula). Great information and presentation. Cheers, Mark * * *

  • @eugengrzondziel1706
    @eugengrzondziel1706 9 років тому +1

    A great video, congratulations for the density of information! Very interesting and usefull for every ham. My very 73 and 55!
    P.S. How about UHF-antenna impedance measurings?

  • @volkerblock
    @volkerblock 7 років тому

    I like this Video. Because I am lazy, I used Freemat (it is free) for calculation.
    --> Vin=64;
    R=50;
    Vx=27.8*exp(i*13/180*pi);
    --> Zx=R*Vx/(Vin-Vx)
    Zx =
    34.2726 + 14.2773i
    -->

  • @acestudioscouk-Ace-G0ACE
    @acestudioscouk-Ace-G0ACE 3 роки тому

    Very interesting, I followed the theory and demo OK but my maths is not up to this level, so I need to put some work in! Thank for sharing this.

  • @ve6wo
    @ve6wo 8 років тому +2

    Thank you for making these videos. They are greatly appreciated :-)

  • @M6MRP
    @M6MRP 11 років тому

    Once again very informative and well presented tutorial, I have also seen this method used for tuning HF dipole traps.
    73
    Phil
    M6MRP

  • @buffplums
    @buffplums 3 роки тому

    This is such a great video. I love your demonstrations they are really helpful and inspiring

  • @kasperandersen7396
    @kasperandersen7396 11 років тому +1

    First of all. Great tutorial and really usefull. In the demonstration the freqency is about 18 MHz, but is it possible to do the same analysis with a higher freqency band, lets say 2.4 GHz? I've imagine that the paracitic effects will have a higher influence with a higher freqency?

  • @MarkBaldridge
    @MarkBaldridge 6 років тому

    So how does the MFJ "directly" measure complex impedance? Would it have a differential amplifier for for measuring the amplitude, and an electrical phase detector of some sort for measuring the time shift?

  • @KD0RC
    @KD0RC 10 років тому

    Excellent video once again Alan! Is this essentially a return loss bridge with the detector split into the two scope channels?
    WOW, You really made me learn something here... I just put my scope across the two detector inputs (top end of the RF xformer...), one channel on each side of my homebrew return loss bridge, and can see visually the peak on one channel and the null on the other... Had to put the spectrum analyzer on zero span to make the measurement. So with the xformer in the circuit, I don't see the same thing as in your video, it looks more like an swr bridge - peak on one side, null on the other.

    • @w2aew
      @w2aew  10 років тому

      It's really not a return loss bridge, but simply an impedance bridge which is used to compare the impedance at the DUT port to a fixed 50ohm resistor.

  • @flyingfrancisco
    @flyingfrancisco 11 років тому

    Hi Alan
    I knew I would enjoy this. Thanks for the wonderful explanation.
    Regards

  • @skitliv
    @skitliv 11 років тому

    I would love to see more about how to apply complex math and do calculations effectively in actual situations. Some tips/tricks maybe? I've studied theory at uni but it was presented in a very non-practical way, not easily applicable to actual circuit design. Seems to me that 99% approximations and 1% ltspice gives good enough results in less time, Maybe audio isn't considered real circuit design? :) Thank you very much for doing these videos! Highly appreciated! Greetings from Sweden

  • @EvandroBubiak
    @EvandroBubiak 10 років тому +1

    Thanks a lot! Very nice, very usefull.
    I want to measure the impedance of a wire antenna (helical connected only on one end on my PCB), can I use this method? need to change something?

  • @manideepdunna827
    @manideepdunna827 3 роки тому

    Thank you for the great videos. I am wondering on what kind of boards do you make solder your circuits? Can you provide a link to them.

  • @mastertheinternetlearningn5266
    @mastertheinternetlearningn5266 7 років тому

    Great Video. Can I use this in one of my classes? To fully master the Internet you need to master the skills you talk about, particularly the math skills. Thank you for this effort.

  • @einball
    @einball 11 років тому

    What a bummer! Didn't think about the ground reference. I seem to use too much C code and too little actual hardware. Thanks!

  • @karmyncraig7220
    @karmyncraig7220 10 років тому

    Can you use this technique to measure the input/output impedance on a transistor amplifier or a filter?

  • @anissastafford8088
    @anissastafford8088 10 років тому

    Very nice thanks. I noticed that the antenna port trace (blue) actually "leads" the reference trace. If the blue trace "lagged" the reference would the angle be considered negative?

    • @w2aew
      @w2aew  10 років тому

      Yes.

  • @syarifhidayatofficial1088
    @syarifhidayatofficial1088 11 років тому

    really a great teaching video,.. easily understood , even it is not an easy subject. thanks for sharing

  • @starlino
    @starlino 4 роки тому

    I am curious if this method can be adapted to NanoVNA, in other words use port 1 as a signal generator, and port 2 instead of osciloscope. Certainly you can measure an antenna just with port 1 using reflected voltage, still I think a comparison of various methods to measure antenna impedance with NanoVNA would make a very interesting video.

    • @w2aew
      @w2aew  4 роки тому

      This resistive bridge is exactly what is already inside of the NanoVNA to sense the forward and reflected signal.

  • @Fireman9143
    @Fireman9143 23 дні тому

    Is there a way to sample actual radio Tx for real world monitoring (without blowing up scope), or is this only effective as antenna analyzer?
    Thanks for all your videos!

    • @w2aew
      @w2aew  22 дні тому

      Yes, look for my video on RF samplers.

  • @Testequip
    @Testequip 4 роки тому

    Excellent. I'm curious, I have two HP VVM's viz 3575A and 8405A. Will the vector voltmeter be far more accurate than an oscilloscope. I used the VVM's a few times to measure resonance but notice there were differences between the scope, spectrum analyzer and vvm. Which is better?

  • @bundylovess
    @bundylovess 10 років тому

    hi alan loved the vid i just noticed that were the 10x probes clip in to, is hooked up befor the 1k resistors can you hook up the probes after the 1k resistors will this still work sorry im still learning

    • @w2aew
      @w2aew  10 років тому +1

      Yes, it will work that way too.

  • @cny02253
    @cny02253 11 років тому

    Super Alan! Great ball park double check to the Antenna Analyzer. Since some cheaper DSO's now have tracking cursors, would any improvement that may give to the delay measurement (to get phase angle) be significant? Also, if one used construction like your attenuator (symmetrical, compact, SMD, SMC jacks, etc) -do you think that would add any significant improvement, especially at higher Hz? Or is that not worth the effort due to scope error limitations.

  • @caravanken1
    @caravanken1 11 років тому

    Thank you for your videos. I am trying to setup this process but cannot find an inexpensive 50ohm through terminator. Will a BNC "T" fitting with a 50ohm end cap work the same as the device you have in the video? I am new and just need a little hand holding.

    • @w2aew
      @w2aew  11 років тому

      It will work reasonably well for lower HF frequencies, and may introduce some reflection artifacts at higher HF frequencies, but they should be fairly minor.

  • @einball
    @einball 11 років тому

    Hey! Nice video! A quick question: Why do you need to measure with 2 channels terminated to 50 Ohms? It would be easier to use one channel over the bridge: If there's a missmatch you will see a (distorted) sinus. You can then tune to 0V on the scope. That would work too, if I'm not mistaken?

  • @scottrharris
    @scottrharris 11 років тому

    Good stuff! It would have been fun to place the scope in XY mode too.

  • @DJ369-Miami
    @DJ369-Miami 10 років тому

    Instead of building this yourself, could I get an off the shelf bi-directional coupler? Any model you would recommend for HF?

  • @researchandbuild1751
    @researchandbuild1751 5 років тому

    Doesn't this also sort of depend on the antenna type as well? I know certain antennas dont show up as 50ohm impedance naturally. Is that what the tuner does basically is match say, a 75ohm antenna to 50 ohms?

  • @wk2w
    @wk2w 10 років тому

    This is an extremely interesting video (both parts). Thank you very much.
    The 50 ohm thru-terminators are interesting. Would it also be possible to use BNC Tee connectors with the input signal running through to a 50 ohm terminator on the female connectors, with the "male" connector into the scope (similar to an end-of-the-run on a coax network)? - wk2w

    • @w2aew
      @w2aew  10 років тому +1

      At HF frequencies, a BNC tee with a terminator can work acceptably when located at the scope input.

  • @coffeecuppepsi
    @coffeecuppepsi 6 років тому

    Just a query, the mismatched antenna is at the other end of a coax ... How does measuring the impedance this way affect the reading? Also after the matching network the radio might see it as 50 ohm.. but the true mismatch is again where the coax meets the antenna?

    • @w2aew
      @w2aew  6 років тому +1

      Correct, the impedance mismatch is occurring at the coax connection to the non-50 ohm antenna. The impedance measured at the transmitter end of the coax will not be the same as the antenna impedance (unless the coax is a multiple of half-wavelengths long). The impedance at the tx end of the coax can be predicted using the Smith Chart - see this video: ua-cam.com/video/ImNRca5ecF0/v-deo.html
      You can place a matching circuit at the antenna (preferred), or at the tx end of the coax. The latter doesn't "fix" the impedance mismatch or the presence of standing waves on the coax.

  • @bassdowg
    @bassdowg 4 роки тому

    Hlo excellent presentation i really enjoyed this, can i do the same with my Nanovna-f ??? Tyvm 73s

    • @w2aew
      @w2aew  4 роки тому

      A bridge like this is exactly what is used inside the NanoVNA. See my video ua-cam.com/video/xa6dqx9udcg/v-deo.html to see how to use it to help with tuning an antenna/tuner.

  • @nbesnerson
    @nbesnerson 9 років тому +3

    Nice. Very much appreciate this video.

  • @StiegeNZ
    @StiegeNZ 11 років тому

    Heya, I'm just at the end of my electronic degree (but need more RF prac!). Just a few conceptual questions I was hoping you could answer. Could you have had the lower resistor of the bridge as 100 ohm and straight paralleled it with the coax heading into the oscilloscope? This may be a bit more complicated when it comes to solving for phase? Also with the 1K res,having larger just means a smaller the signal going into the oscilloscope?
    Thanks

  • @fishyrider3528
    @fishyrider3528 7 років тому

    Hy, first of all thank you for the knoledge. You are a great techer. Second i have a request. I want to align an fm module for my radio. I do not know the impedance at the dipol antenna imput and how to connect the sig gen to it. I have a rigol sig gen with fm modulation and a rigol scope. I can not find a detailed enough video on how to determine the impedance of the input dipol antenna and to connect the sig gen to it to match the impedance. Pls help.

    • @w2aew
      @w2aew  7 років тому

      The easiest thing to do is to connect the dipole antenna, then attach a small wire (non critical) to the siggen output, and let the dipole on the radio pick up the signal. It will be much stronger than anything else around.

  • @NeilCaulfield
    @NeilCaulfield 9 років тому

    I have a CB radio I found at the dump and it powers on, but I have no idea if it transmits properly. How should I go about testing the output frequencies of the radio itself? I have a pretty nice 100 MHz oscilloscope that should be able to read the output from the RF connections. I should see an AM carrier wave but is there any kind of load that I should connect to prevent damage to the transmitter?

    • @w2aew
      @w2aew  9 років тому

      +Neil Caulfield The transmitter should be loaded with a proper 50ohm dummy load that can handle the power of the transmitter. You can monitor the RF output using an RF tap/sampler. Here's a video on that:
      ua-cam.com/video/0Kk_N_TpDeo/v-deo.html

    • @NeilCaulfield
      @NeilCaulfield 9 років тому +1

      +w2aew awesome thanks! I was able to see carrier wave, appears to transmit properly
      pretty nice find in the trash, will have to get antenna for it

  • @pu2clr
    @pu2clr 11 років тому

    Very nice video.
    This idea is very useful to build a auto-tuner.
    Thanks.
    PU2CLR,
    Ricardo.

  • @afterthought138
    @afterthought138 11 років тому

    Hi Alan. Great video as usual! What material is the board used to mount your bridge circuit made from? It looks like copper-coated perf board of some sort. It looks nice for shielding purposes while still being easy to drill holes through.

  • @tonybell1597
    @tonybell1597 11 років тому

    Great video.... Probably need to hit the text books now and work out what all the rectangular math is all about!

  • @StanleySeow
    @StanleySeow 10 років тому +2

    Hi, firstly, I would like to mentioned that you have lots of very good video with very simple and easy to understand explanations... Keep up the good work!!!! I've made SWR bridge and was feeding it with a AD9850 modules that can output 1Mhz to 30Mhz m just nice for the HF bands... I just follow all the circuit that you did and I was able to tune HF antenna using an antenna tuner. I find the AD9850 voltage is rather low at 20Mhz and above ... Can you suggest a method to amplify the output voltage of the AD9850 ?? Does the 50R/50R voltage divider causes the readings on the oscilloscope to read a low voltage ? Thanks ,,,

    • @w2aew
      @w2aew  10 років тому

      Often times a drop off in amplitude at higher frequencies is a circuit layout problem - so it is difficult to comment why you have a drop off. You may be able to improve the layout to bring the amplitude up. A simple common collector amp can be used as a buffer (if the issue is simply loading), or a common-emitter amp would give you some gain. You'd have to follow the common-emitter amp with a common-collector amp to regain the low output impedance.

    • @StanleySeow
      @StanleySeow 10 років тому

      The drop in amplitude as freq increases was stated in the AD9850 datasheets. Can you give some part number examples and sample circuits on the common collector/emitter amp as a buffer ? Could I suggest you do a video on the topic to how to increase the gains on RF signals ?

    • @w2aew
      @w2aew  10 років тому

      Stanley Seow That's a good idea for a video, but it will take me quite a while before I get to it. Each video is often weeks or more in the planning and preparation stages... You might get more prompt answers by consulting the applications engineering department at Analog Devices - the maker of the AD9850 - they may have some reference designs already prepared.

    • @StanleySeow
      @StanleySeow 10 років тому

      Ok thanks... let me do more readings and lookup their application notes...

  • @yoniziskind2115
    @yoniziskind2115 7 років тому

    Great vid! one question though, can I implement this concept in evry input impedance measurement?(such as amplifiers, mixers, etc)

    • @w2aew
      @w2aew  7 років тому

      Yes, it should work for other devices - but layout limitations means that it will likely only be accurate for HF and below.

  • @leobotler
    @leobotler 9 років тому

    Very good video!
    Could you please explain why do the oscilloscope needs 50 ohms terminations?

    • @w2aew
      @w2aew  9 років тому

      Leo Botler Yes, the terminations are added to the ends of the cable to prevent reflections of the RF signals that are coming down the line. If your scope has 50 ohm terminations built in, you can use them instead of the through terminations.

    • @leobotler
      @leobotler 9 років тому

      *****
      First I would like to thank you for your answer, but I was not clear enough in my question.
      I didn't understand why you placed a big resistor (1Kohm) in series with the oscilloscope and also a 50 ohm termination, once the input resistance of most oscilloscopes are already very big (>1Mohm). How does it avoid reflections?
      If you have a reference that can help me understand it I would appreciate!

    • @w2aew
      @w2aew  9 років тому

      Leo Botler The big resistor in series with the coax is placed there so that the 50 ohm resistors in the bridge dominate the impedance seen at the bridge nodes. Once RF signals are in a transmission line, the current/voltage waves assume a relationship of Z0, the transmission line impedance. If the transmission line is not properly terminated, then there will be a reflection will will affect the amplitude of the signal which will be frequency dependent. So, by properly terminating the lines, no reflections occur. You might find this video helpful:
      ua-cam.com/video/g_jxh0Qe_FY/v-deo.html

    • @leobotler
      @leobotler 9 років тому

      ***** Thanks! Also a great video. Isn't this reflection already avoided by the 50ohms resistor connected to the ground? I mean... The reflection you avoid in the oscilloscope input is happening on the 1kohm input... Am I wrong?
      The input impedance in the path going to the oscilloscope is much bigger than 50ohms anyway, so in my understanding you could place the oscilloscope directly on the antenna.

    • @w2aew
      @w2aew  9 років тому

      Leo Botler There are RF signals injected *into* the pair of coax cables that lead to the scope through the 1K resistors, and they travel down to the scope. When they reach the scope end of the coax, they need to see a 50 ohm termination to prevent a reflection at that point.

  • @mick2458
    @mick2458 9 років тому

    is there a simple method for checking ceramic filters....the 3 and 5pin types?

  • @raghutumati5178
    @raghutumati5178 7 років тому

    Hi Alen. I have a impedance matching question. I'm working on a hobby FM transmitter circuit on a 10/15/40m radio band. Finished designing the Clapp oscillator, LNA and output stage (PA). But Im not sure how I can connect an antenna to my output stage. Can I just connect a wire of a particular length to the output of my transistor (BJT). I would assume that there has to be some sort of matching needed here. If so, how do I go about this without an antenna tuner?
    P.S Hope your ankle is healing well!!!

    • @w2aew
      @w2aew  7 років тому

      It really depends on the output impedance of your transmitter. You'd ideally want to match that. Otherwise, just design the antenna system for resonance. However, this brings up the bigger issue of legality. In the US, these frequency bands are not license-free. Portions of them are reserved for amateur radio use, and FM is not permitted on the 15m and 40m bands, and is reserved for a portion of the 10m band.

    • @raghutumati5178
      @raghutumati5178 7 років тому

      Thanks for the reply. You mean the small signal impedance of the transmitter right? How would I determine the impedance of a wire that I'm using as an antenna. Do you have any practical references that could help me to get more info?
      Thanks for bringing up the legal issue. Ill have to re-check the bands to see where it would be legal.

    • @w2aew
      @w2aew  7 років тому

      The most accurate way to predict the input impedance of the antenna would be to use one of the NEC-based modelling programs. Lots of good information here:
      www.arrl.org/antenna-modeling

    • @raghutumati5178
      @raghutumati5178 7 років тому

      Thank you Alan!!!

  • @uiticus
    @uiticus 5 років тому

    Do you have a video explaining both polar and rectangular form calculations?

    • @w2aew
      @w2aew  5 років тому

      I don't, but here's a summary:
      www.varsitytutors.com/hotmath/hotmath_help/topics/operations-with-complex-numbers

  • @boonyang88
    @boonyang88 8 років тому

    can u do a video on smith chart and impedance matching . thanks!

  • @Kennynva
    @Kennynva 8 років тому

    HI...do they have this built into some of the high end Icoms or Kenwood transceivers of the ones...I dont know if they do..I do not have like 5k to 10k to spend on these type receivers..

    • @w2aew
      @w2aew  8 років тому

      Not this specifically, but they do have built in SWR bridges that can measure VSWR.

  • @DeeegerD
    @DeeegerD 9 років тому

    Another question if you don't mind? Do impedance matching circuits (ie: antenna tuners) create loss in power?

    • @w2aew
      @w2aew  9 років тому

      +Digger D Generally, very little, if they are made from capacitors and inductors. Since the voltage and current in a capacitor/inductor is 90 out of phase, they do not dissipate power. They store energy (in electric field or magnetic field), then return it to the system/circuit. The main losses are generally due to resistance in the wiring, inductor, switches, etc.

    • @DeeegerD
      @DeeegerD 9 років тому

      ***** I was thinking that but some hams on a video were debating it the other day. If there is no impedance... (except for normal losses as you say). Thanks again.

    • @w2aew
      @w2aew  9 років тому

      +Digger D RF currents can be high in high-Q tuned circuits which can lead to higher resistive losses in the tuner. Also, if the tuner is located in the shack, then the feedline from the tuner to the antenna will be operating with a high SWR, which can also lead to losses.

    • @DeeegerD
      @DeeegerD 9 років тому

      ***** Ok, thus the invention of the remote antenna tuner. Good to know and thanks again.

  • @Cadmandu
    @Cadmandu 9 років тому

    Hi Allen,
    This is a great experiment. I want to try this on my 40 meter dipole. I am having a hard time finding a 5% 50 ohm resistor. Can you tell me if using two 100 ohm in para will be okay? I did find 47 ohm and 50 ohm cement wire wound. I guess the wire wound are bad for RF please advise.
    Thanks Dan 73 W3DKY

    • @w2aew
      @w2aew  9 років тому

      The two 100 in parallel would work fine. Also, 51 ohm are fairly common and only 2% from the nominal desired value.

  • @StanleySeow
    @StanleySeow 7 років тому

    I had some AD8307 log amp/detector, can I hv the output, instead of going to the scope, goes into the AD8307 to detect the forward and reverse voltage similar like a directional coupler ? Thanks

    • @w2aew
      @w2aew  7 років тому +1

      You certainly could use a log amp/det to indicate the level of mismatch, but you won't get any indication of the type of mismatch (you lose the phase information).

  • @glennwoodward77
    @glennwoodward77 5 років тому

    Great video! Love all of your circuit build videos. Would this method work when trying to test and tune 2.4 or 5.8ghz antennas?

  • @fmbroadcast
    @fmbroadcast 9 років тому

    Hey, I love your video, amazing !!
    At 10.53 you speak about non linear curve about the voltage divider. How did you got this curve ? I am not sure to understand ? Because when I plot Vx=(Vin*Zx)/(Zx+50) I don't get this curve. Can you guive me more details ? Kind regards

    • @w2aew
      @w2aew  9 років тому

      fmbroadcast Are you sure? Did you change the x-axis to Log? If you spot check some numbers, they call on this curve. For example, for Zx=10, Vx calculates to 0.333, which is on the curve. For Zx=100, Vx comes out to 1.333, which also lands on the curve...

    • @fmbroadcast
      @fmbroadcast 9 років тому

      ***** Hello, thank you a lot for your reply. Ohhh yes okey you plot the x axis to Log Okey !! Yes i got the same value, Zx=10=> 0.333 and Zx=100 => 1.333.
      Frantastic !!! I love your video !!! Feel free to suscribe to my channel ;)
      Kind regards

    • @fmbroadcast
      @fmbroadcast 9 років тому

      ***** It's me again, something that tilt me. On the scope, the yellow trace represent the signal from the reference voltage divider is that correct ? we can see at 7.20 that when you match the antenna load, the yellow trace make some tilt in amplitude and phase, I guess because the signal generator impedance is of course not null but in the ideal case, is the yellow trace should have to change in amplitude and phase ? May be i miss understood something. But this is facinating me.

    • @w2aew
      @w2aew  9 років тому

      fmbroadcast Yes, the generator's output impedance is 50 ohms, so the output will vary as the applied load varies.

  • @ritmo1130
    @ritmo1130 7 років тому

    Trying to use this gizmo to tune a broadcast tower ATU, keep you posted of what I get, just wondering if someone has tried on BC towers before ??

    • @w2aew
      @w2aew  7 років тому

      I just hope that you do it at very low power!

    • @ritmo1130
      @ritmo1130 7 років тому

      :-) please don't be concerned as I will use a vintage GR oscillator. Also I found some 5 watt 50 ohm resistors just in case.

  • @3cu14rs
    @3cu14rs 11 років тому

    This was a great vid, thanks for taking the time to explain it to the rest of us :) After measuring the impedance, how would you go about designing a dedicated matching network?

    • @peterporkolab2800
      @peterporkolab2800 4 роки тому

      Watch his video about using Smith's chart, and You will know.

  • @clintonmagro
    @clintonmagro 4 роки тому

    I have a question with regards to your signal generator, in your case you configured your signal generator to 18.130Mhz. So if I wanted to fine tune an antenna for an 868Mhz tranceiver, I would need a signal generator that is capable of generating 868Mhz as well as an oscilloscope that can sample up to 1Ghz?

    • @w2aew
      @w2aew  4 роки тому +1

      Yes, but at these frequencies, the parasitics of connecting probes will alter the results. Thus, at these frequencies, a scope + signal generator are really not the best tools to do this job. A network analyzer is likely a better solution.

    • @clintonmagro
      @clintonmagro 4 роки тому

      @@w2aew Thank you Sir!

  • @SlowburnFoos
    @SlowburnFoos 10 років тому

    Impressive video! Where did you get the antenna tuner from?

    • @w2aew
      @w2aew  10 років тому

      The tuner is the ZM-2 Z-Match Transmatch kit by Emtech. Here is the link:
      emtech.steadynet.com/zm2.shtml

  • @rccar354
    @rccar354 Рік тому

    nice video
    THANKS
    forgive my ignorance but what is the difference between am Antenna Tuner and an Antenna Analyzer ?

    • @w2aew
      @w2aew  Рік тому +1

      An antenna "tuner" or transmatch is an adjustable impedance matching network that is placed between the transmitter and the antenna, and is adjusted to transform the impedance of the antenna system to something that matches the impedance desired by the transmitter (usually 50 ohms). An antenna analyzer measures the complex impedance of the antenna system, using it's own built-in RF source. It does not adjust anything, but rather can be use to examine the changes in impedance made by tuning the antenna system.

    • @rccar354
      @rccar354 Рік тому

      @@w2aew Something occurred to me while reading this... that the math does not seem to encapsulate antenna geometry. [ MAYBE I AM WRONG] I was reading a riddle of Analogy between Earth and Man and Man and Mind.
      26:17 || 25.8 + 30 : 24
      the difference between 30 and 25.8 being 4.2... some form of energy modulation perhaps
      two primes [ 13 and 17] and a "square" [ 25.8 squared is close to 666 minus 0.36 or 0.6 squared] 'move' in the system. So, what might be the relation, if there is one, of 665.64, 0.36 and 666 ?
      if my intuition is right
      one system is a 3- dimensional antenna system
      the second is a 2-dimensional antenna system [ not quite but close enough for our intents and purposes]
      If both systems pertain to transceiver systems ... we have food for thought on Energy and Angular-Spin systems that the Schrodinger equation tried to explain also.
      So, I guess one 'new' system attempts to show that there is resonance or frequency - matching between
      Earth and Mind.
      The brain has two-hemispheres as does the Earth.
      one [the brain] operates on a two-dimensional plane [ SURFACE OF THE EARTH] while the other [the Earth] operates
      on both two-dimensions and three dimensions... or maybe system X [ Man - Earth - Galaxy System] and
      {system X minus 90 degrees} [Mind - Man - Earth System]
      Hey, I am just spit-balling my intuitive ideas here to see if a snow-ball can make an avalanche.
      The difference between 3 dimensional and 2- dimensions being 90 degrees or 2xPi / 4 radians
      The Square [90-degree 'inferior' system within the parent 'superior' system] and the Compass comes to mind.
      Your video sparked by intuitive process. Thanks....
      Resistance, Capacitance, Inductance make me think about 'magnetic refraction'
      and the possibility of uni-directional energy flow similar to a laser which would theoretically extend
      transceiver range.
      My next question is ... Are there such things as 'laser' radio-transceivers ?
      SEE
      www.arrl.org/laser-communications
      some terms
      Resistance [AMPLITUDE], Reactance[ANGULAR VECTOR], IN COMPLEX Impedance SYSTEMS
      WHICH CAN BE PERCEIVED AS EITHER POLAR FORM OR RECTANGULAR FORM.
      SOME MIGHT LOOK AT ETHER - ETHERIC ANNANAS [NEGATIVE MAGNETIC FIRE] AND ANIONITES [POSITIVE MAGNETIC FIRE] AND SPECIFIC SPEED AND DYNAMIC FORCE IN TRANSFORMATION OF ENERGY SYSTEMS. IF ETHER IS LIKE A TUNING FORK THEN WE ARE QUANTIFYING AND QUALIFYING
      RESONANT ENERGY INTO AMPLITUDE AND AXIAL SPIN.

  • @achernarscardozo69
    @achernarscardozo69 2 роки тому

    Con este procedimiento no se determina la impedancia de la antena sino la impedancia del cable y la antena. Con diferentes longitudes de cable pueden obtenerse resultados diferentes.

    • @w2aew
      @w2aew  2 роки тому +1

      Yes, this is true - you're really looking at the antenna *system* impedance, including the impedance transformation/rotation that is added by the transmission line. At the end, this is OK, because this is the impedance that will be seen at the transmitter.

  • @hubercats
    @hubercats 3 роки тому

    Another great video. Thanks!

  • @ibsrensen1911
    @ibsrensen1911 3 роки тому +1

    you have a great way of explaining even the most stupid people living - walking or whatever on earth they dó, actually get- it! 😎
    I used your video to explain how an CB antenna tuner is working.
    Trying to figure out a way of making non-technical friends understand things like this is not always a easy task.😂
    Purely 👍👍👍 from me, keep it coming 😁

  • @Jjacobs1986
    @Jjacobs1986 11 років тому

    You're a mad scientist. I love it.

  • @DeeegerD
    @DeeegerD 9 років тому +1

    If you do not have pass through terminators could you use T connectors with one end terminated with 50 ohms?

    • @w2aew
      @w2aew  9 років тому +1

      +Digger D Yes, for HF that will generally work well.

    • @DeeegerD
      @DeeegerD 9 років тому +2

      ***** Great, thanks again.

  • @dyamiestudio
    @dyamiestudio 9 років тому

    hello I hope u are fine.
    can u help. please tell me how to calculate or find the values to the components to build a cristal oscillator circuit that generates 3 Mhz or 2Mhz?

    • @w2aew
      @w2aew  9 років тому

      Congo Beats ( Congo Production ) See this video on how to build a crystal oscillator, and simply use a crystal with the desired output frequency.
      ua-cam.com/video/blalAktxFoI/v-deo.html

  • @johnrowing3306
    @johnrowing3306 Рік тому

    Try switching to X Y on the scope