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- čas přidán 4. 07. 2024
- This video describes the basic properties and specifications for directional couplers, and shows their basic operation on an oscilloscope. Typical applications are discussed, along with a practical example showing how to sweep the VSWR, or Return Loss, of an antenna using a directional coupler and a spectrum analyzer with a tracking generator. The resulting return loss measurement is compared to the SWR measured on an MFJ-259B antenna analyzer.
Datasheet for the directional coupler used in this video:
www.minicircuits.com/pdfs/ZFDC...
My video on the basics of Tracking Generators:
• #62: Basics of Trackin... - Věda a technologie
I just got a directional coupler, because of this video and tried it out with a lot of success. I am a big fan and watched a lot of your videos. They are extremely good, not trivial, but very understandable. In my youth I was a ham operator. In these days the frequencies and the budgets were much lower than now. I enjoy the revival of my "RF hobby" (also with my first spectrum analyzer), now paired with microcontrollers.
Thank you very much for your effort to put your knowledge online!
...and it is a pleasure for me to meet the two youtubers favorite by me on the same page !!! Great!
@@picwiz2 same to me ;-)
A suggestion for a video might be the difference between a directional coupler and a return loss bridge... The insertion loss for a bridge seems to be much higher... Enjoy your videos, very very informative...
Alan, can't thank you enough for all your videos and expertise. You inspire many to dig deeper into the technical aspects of radio and electronics. Thanks again!
I could watch these many times over as they have great density of. Information. Ty for taking time to do these clear tutorials as always .
Alan, This is the first video of yours I watched and you are an amazing instructor. I sincerely thank you for taking the time to explain directional couplers to me!
Thank you so much Alan for teaching us this. I used a directional coupler tonight to look at a chinese fpv antenna and found out it wasn't exactly what I thought it was. All thanks to you! Mike K8MB.
this is most professional channel about electronics in educational aspect on yt. Thank you Alan
Thank you, I'm glad you enjoy it!
I'm glad you did this video. I recently purchased a spectrum analyzer with a tracking generator. I wanted to look at S11 and VSWR with it and there is a directional coupler made for this analyzer that cost around $700.00. However, that Mini Circuits directional coupler does the same thing for under $100.00 fantastic! I really enjoy your video's lots of good information. Thanks!
Have been home brewing some amateur osc/amps and an antenna for 1.269 GHz. I have the same type coupler. Your video is a great help. I am using attenuators and crystal detector to get my measurements. Great video!
I learn something new every time I watch this video and I’ve watched it many times 🤓 thank you
thanks for the video - it's the best description of the operation of a directional coupler I've found.
I am impressed and this helped me greatly figure out how to measure the VSWR on one of my antennas at work.
Dip the plate, lower the current. Efficiency of a tube with a directional coupler used as a sample port. Used them with gridded traveling wave tubes as well. Great channel you have!!
Thanks for your informative and educational videos. It's good to know how and why something works, and not just what it does.
Good stuff!
At my former job I always had access to a network analyzer for these type of measurements. It is funny that I didn't know there was a such thing as a tracking generator for a spectrum analyzer as a 'lower tech' way to measure a coupler's response. Very nice tutorial, I enjoy watching them.
Really good video, I was about to ask you to make a video about directional coupler and boom here is it. Thank you very much.
Wow! Just the explication I've been looking for for a very long time. Thanks!!
Glad it helped you out!
I'm learning so many things from your channel.. Thank you very much... 👍👍👍
Terrific video - that was _exactly_ what I wanted to know, very clearly demonstrated. Many thanks.
That was very educational and professionally presented sir. Thank you.
Thank you for taking your time to make this video! I learned so
Much. I recently purchased a Rigol DSA815 TG and a ZFDC 20-4 coupler. I was confused on using the coupler till you cleared it up! 73's David. K8KEM
Wonderful tutorial! Thanks for posting.
Great video! Thanks for providing this good (and well presented) info. Cleared up a few things for me. 73s!
Great explanations !! I just learned something from you sir.Thanks.
this was very clear. thanks. I will give this a go building my new antenna
Excellent work and execution done
Excellent video. Thank you very much for sharing it. Truly useful information.
Your video helped me a lot today. Thank you.
Cannot thank you enough for this explanation.
Finally I understand how a coupler works. Thanks
Absolutely great video sir!
Great video. Thank you so much
Very interesting, great video. Thanks!
Thanks, It was great, specially when you learned all of this just in the book
Keep going ;)
Thank you very much for taking your time to make this video! It's appreciated 73's David. K8KEM
Very well explained as usual Thanks!
very clearly explain for a directional coupler
thanks
Thank you!!!! This was fun to watch. 73!
Thanks, very helpful video well presented.
Very interesting, thank you.
Thank you by this clear explanation !
Thanks for this video, I recently got a Rigol DSA-815TG and also a directional coupler, but I have a lot of problems with ripples in my return loss plots. I tried to connect a 6dB or 10dB pad between the TG and the SWR bridge, but the ripples keep persisting. I've tried using my 10 meter long coax for HF, and also a good quality 1 meter long SMA cable, but the ripples are still noticeable. However, when using a short piece of SMA cable (15cm or so) the ripples are almost completely gone. Would connecting an attenuator between the SWR bridge and the spectrum analyzer input achieve anything? I'm waiting for some N to SMA adapters so those should come in tomorrow, I can't try it out yet. Thanks again!
Thank your for this video... as a junior RF engineer this was informative. Maybe some one has already asked but can the coupled port be used to inject a sample signal? How would that work?
Amazing! Many thanks!
Very understandable. Thank you!
Excellent tutorial thank you
Great video! This is the second time I watched it, and can't tell you how much I appreciate the work you do in producing these. Very helpful to us folks returning to the hobby! I do have a question. Rigol sells a "SWR Measuring Kit" for their spec analyzer that pretty much looks like one of these couplers and a few fittings stuffed into a fancy box (with matching price). Is that all it is? It looks like there might be software also, but I'm guessing that it's just minor stuff - say, calibration data and a few automation procedures - for whatever coupler they used. What do you think? Thanks again!
It is likely a directional coupler and software.
I have the same mini circuits directionaql coupler that you have there and an eagle return loss bridge. I bought one of those el cheapo green directional couplers off ebay and I was very surprised at how well it performs
A good video. Interesting is that the waveform voltage on channel 1 increased when the load was increased from 50 ohm to 1 meg ohm. And the power transferred was then less than with the 50 ohm load even though the waveform voltage increased. If you known what the increased voltage was across the 1 Mohm load, you could compare the transferred power to when the load was 50ohm.
Awesome! Thank you.
Great video!!!!
“Hope you learned something”. You bet. Thanks Alan, Cheers, Mark
Hi Allen ... great info. Could you perhaps do a video on the MFJ analyser as to how to properly calibrate it?
Thank you & 73,
Neil,
K7WK
I ran this experiment on a 1.27 GHz antenna using a signal generator, spectrum analzyer and compared 2 directional couplers. 1 Mini-Circuits like in the video and a Chinese model. The results were significantly different. Mini-Circuits return loss was 18.51 dB Chinese model was 42.41 dB with a much narrower trough. The frequency also shifted 84MHz. Since I don't have a tracking gen, I sweep the frequency range and use "Max Hold" until the screen fills in and use that as the '0' reference. I have repeated this experiment multiple times in different frequency ranges with similar results. Any Idea why the results would be this different between 2 couplers?
Great great great .. thank you sir .
Great video thanks
Excellent.
gave it a try on a 2M Jpole type antenna, worked great. I'm confused about return loss bridges and when and why to use them over a directional coupler.
+Mark Butterworth Return loss bridges output a DC voltage in proportion to an impedance mismatch, while directional couplers output a sample of the RF energy flowing in a chosen direction. Either one can be used to characterize the mismatch of an antenna system - it all depends on how you want to process/measure the reflected signal.
Yep, coupled ports are used to monitor antennas along the path. Basically the load is coupled pre and post wherever it goes next.
Excellent video. I have a question... if I use a basic and inexpensive antenna tuner like RigExpert AA-600 to observe the tuning dip, will that be as good as the spectrum analyzer method you have used?
+Debamalya Banerjee Yes, an analyzer like this can illustrate the return loss just as well as the spectrum analyzer.
wow great video thank you!
Thank you, sir, I have 2 questions.
1. Can I connect an RF signal generator instead of an Antenna at 9:37 to measure the output impedance of the RF signal generator?
2. Can you explain the difference between VWSR Bridges & Directional Couplers?
If you have a chance, could you explain them to me?
Thanks for the sensational tutorial. I'm a bit lost @ 6:20 however. @ 5:30 you reversed the input and output; i.e., you put the signal into the output port of the device, and connected o-scope channel 1 to the input port of the device, deliberately, to prove a point that the coupled port is profoundly isolated from signals that ENTER (generally inappropriately) at the output port. Then you start another discussion @ 6:20 without clarifying whether or not you restored the original connections; or if you left intact the reversal.
OK OK... I get it. @ 10 (when you're using the spectrum analyzer) it's obvious you're still using the directional coupler backwards.
Hey, I learn something every day.
This was really cool. Thanks again.
These devices are easily faked at production, I should know having 20 years RF inspection background, a magnet put on the unit will simulate max or min testing, production route card dating can be faked for endurance testing, good xrays swapped for bad, vibration testing done by running off plots only without vibrating the device, I could go on & on. I earned a wage for 20 years by thinking up random numbers in a range every day for microwave devices. lol just watching that video it reminded me of when we had to demonstate isolators & circulators working on an analyser , one customer took one look at the settings & took off all the offsets which were programmed into it to make it look like the devices were compliant (facepalm)
Glad you "got it". Sorry if it was a confusing road...
I have been 'standardized' by using a 1dB pad for the impedance leveling.
So could this be used with an rf probe on the reflected side to isolate an impedance mismatch in a circuit?
Very very useful vedeo .thanks keep it up
Than you. In Algeria, this informations is confidential and monopolistic
I have a directional coupler with no data sheet. What test can I perform to determine its frequency range. I have a 1-4ghz sweep generator and a 2.4-2.5ghz spectrum analyzer. Ports are in, out, -30db, and ISO? Made by RF Power. SDC-182-202-R1-30
Thank you sir!
Hi,
I didn't know for directional couplers. I'm learning basic of RF and transmission lines...
I tried to create directional coupler of piece of cable. Terminated output, give me 0 on coupled output. When output is open, coupled signal and signal from source are in phase, which is expected, but when I short output, signals are about 90 degrees out of phase. Why 90? I expected 180. Is it my setup problem or I didn't understood.
Thanks
great video :D
very nice video!
Awesome Thank you 😊
Thanks a lot for this video w2aew. Learnt a lot from it. Directional coupler is a neat device. Very nicely explained. The only thing a little unclear @10:00 is that we are viewing the coupled port correct?
Yes, the analyzer is measuring the coupled port which is sampling the signal being returned from the antenna.
why you don't using MDO3104 spectrum analyzer ?
Noise function will not work for this measurement ?
Yes, I could've used the noise generator and spectrum analyzer in the MDO and it would've worked fine. However, I showed this technique to show the filter responses in the SDR radios and figured that viewers like yourself would recognize that this would be an alternative way to "sweep" the antenna.
Nice video. I'm a new HAM and I'd like to characterize the 20m half-wave dipole antenna I recently installed in my attic. Can I use this technique without generating RF interference from my antenna?
+jimhollister50 Sure - any method that uses a very small amount of power would be acceptable.
I got an EE degree 50 years ago and at some point the prof zipped through how a directional coupler works. I didn't understand it but I still managed to use couplers and hybrids through a career. NOW I'm retired and I don't need the devices but I want to learn how they actually work. Can't seem to find an explanation. I guess everybody just uses them. But if you look at a coupler logically, it's like a bumblebee-- bumblebees are not supposed to be able to fly. Likewise for the directional coupler--can't fly and shouldn't divide out the forward and backward signals. They are too small. If you stick a stake in a creek or river, it can tell you the level of the water -- analogous to showing the vector sum of the voltage at a point on a transmission line. You have no way of knowing the direction in which the water is flowing. The same should be true of a "directional" coupler. At microwave frequencies maybe there is room for more "direction finding" components. But a classical directional coupler for a 7 MHz sine wave is usually less than 6 inches wide--at 7 MHz a quarter wavelength is about 40 feet---CAN'T WORK. It's a bumblebee. I'm still searching for an explanation. For now, I treat directional couplers like UFOs--some people say they've seem them--personally I haven't. Don't believe in them myself.
Firstly, you are a great instructor. Being licensed in 1953 as W5WTN, a lot has changed. I wonder if you are familiar with the Rogol SA. I have the 2 Ghz version and when I try to use the normalization function, the soft key is grayed out. The instructions state to change the settings to Dbm, which I did. No cigar. If you have any suggestions, please let me know.
Keep up the good work.
Best 73's Eddy W5WTN
Can’t say how many times ive watched this video. Can i add that at the moment you are seeing reflected signals that they may also be out of phase at 7:39 ?
Thanks for video Alan, great as always... I am new to RF stuff and recently have bought a spectrum analyzer with a TG, also built home brew directional coupler and trying to figure out how it works.
My question is what steps should i take in order to determent what is capable for ?
In other words if you have an unknown directional coupler how would you determent its characteristics or verify with a datasheet if happens to know the part number? What would you look for to verify that it is performing as stated or it is defective, also its frequency range, all by using a spectrum analyzer with TG ?
You can start by checking the forward and reverse coupling characteristics. Connect the TG to the RF input, connect known good broadband 50 ohm terminations to the RF output and the REV port on the coupler, and then connect the FWD port to the SA and sweep it. You should see a relatively flat response at the rated coupling ratio (10dB down, 20dB down, etc.). Then, reverse the FWD and REV connections and sweep again. With a good termination on the RF out, you should have very little reflected power so the REV output should be very low. Then, remove the 50 ohm termination from the RF output, and sweep the REV again, this time you should see a response similar to the FWD you saw earlier.
Alan, great video.
Question, how accurate do you find the MFJ to be? I see it being used by most hams, including my dad, but I am aware that numbers on an LCD don't always reflect the truth. On the other hand, if it is a tool used by most it can be considered as a standard no matter the downsides. Would it be valuable for you to make a video on the MFJ pointing out how to correctly interpret the values displayed by it? Regards, CX6BT
I've found the MJF to be accurate enough to be effective. One thing you have to be careful with is that when testing antennas, signals that are picked up by the antenna may couple into the bridge and upset the readings. I'll think about doing a few vids on the 259B in the future.
What a Both great and useful Video, congrats!!
I just have one question what could i say between use Directinal Coupler and a Bridge to measure SWR for an antenna?
Thanks
You can leave a directional coupler in place when operating, but you can't do that with a bridge.
@@w2aew Now, I got it
Thanks a lot!!
Hey I really like this video. I am considering in buying a spectrum analyzer for tuning antennas on a PCB (chip antennas). But they can be so damn expensive! So I was wondering, would a MFJ-259B do the trick? Thanks in advance!
What power rating on an attenuator would you recommend so that an antenna as a DUT doesn't drive the tracking generator by picking up arbitrary rf signals from the air?
The MFJ-259B only goes up to 470MHz, which seems a little low for PCB chip antennas. But, if this is within your frequency range, this unit works pretty well. It will give you VSWR as well as impedance and phase - it just can't distinguish between positive or negative phase angle.
It would be difficult for me to recommend an attenuation value because I don't know you're situation (how tightly coupled your antenna will be to the off-air signal, what kind of power levels you're dealing with, etc.).
Great video. Very helpful. I'm interested in monitoring the SWR and forward power off of a 1000W linear amplifier. How would the design change for something like that? Or to ask this differently. Can you put the swr meter and coupler between the transmitter and the linear amp and be fairly confident that the reverse signal will not be changed appreciably by going through the Linear amp?
The reflected signal will NOT be transferred backwards through the amp. You'll have to put the directional coupler between the amp and the tuner/antenna. Here's a good application note on this: www.analog.com/en/technical-articles/log-amps-and-directional-couplers-enable-vswr-detection.html
@@w2aew Thanks for the link. Very helpful.
@@w2aew This brings me to another question, have you ever done a video on using test equipment, especially a scope, to test a receiver for dB gain or losd, notch configuration, Selectivity, etc? This may be too broad of a subject, but there doesn't seem to be a lot of information on basic testing of receiver health using a scope, for example. Thanks again for all of the great videos.
At 4:23 you refer to 20 dB being "1/10th the power", but isn't it 1/10th the voltage, and 1/100th the power?
I found this video very informative, and a great explanation. If the mood comes to you, I would like a video that explains a few of the ways couplers work.
Ack! I hate when that happens! Of course, you're right. I've added an annotation to correct my mis-spoken narration.
gets tricky when you speak volts and dbm
@@w2aew 20 db down on power is 1/10 of voltage since "P-dbm = 20 * log(V-mpvv) - 56". so 1/10 of voltage is 20 db down. I did this calculation on my video: czcams.com/video/_1R9fDVkjwk/video.html
20 db down on power is 1/10 of voltage since "P-dbm = 20 * log(V-mpvv) - 56". so 1/10 of voltage is 20 db down. I did this calculation on my video: czcams.com/video/_1R9fDVkjwk/video.html
Hi,
I have a question. When you are testing the antenna, the signal from the tracking generator to the antenna is reflected back to it for the non-resonating frequencies. Won't this interfere with the subsequent signals sent from the tracking generator?
+Shalini Srinivasan It can, which is why an attenuator is often included in series with the TG output. However, if the end goal is to achieve a good match (no reflection), then the point is moot because there will be no reflection at the desired point.
get a dual directional coupler to measure reflected power. I have always been taught to terminate at the load, not at the source. have you heard this or think it makes a difference?
Yes, of course you want the load to properly terminate the line to minimize reflections.
Hey,
Is the output seen in the spectrum analyzer the actual s11 curve, as the output is obtained from a different port than the input? It seems to contradict the common definition of s11.
+Pranjal Paliwal A network analyzer uses a directional coupler to measure the output and reflected power at each port - so there's basically a coupler behind each port of a network analyzer.
Hello, I thoroughly enjoyed this video! I own a Tektronix 494p and would like to test SWR on my homemade antennas in the 5.8g frequency. My analyzer doesn’t have a tracking generator. What form of signal generator would you recommend if my only intent for use is swr on my antennas? Thanks for the great content!
You need an RF sweep generator that will sweep the range you want to test. Set the sweep rate high and the scan rate of the analyzer very slow. You will get an envelope of the response using the setup as in the video. I do this for my drone antennas.
glasslinger thank you, I managed to get a very cheap sweep generator development board ranging from 35mhz-4400mhz and use a frequency multiplier to get me up to the 5.8ghz if testing that band. Works great! Thanks for the reply
Hi Alen. I cannot find what is mix power, that this direction coupler can handle? I mean, can I use this for monitor 40 or 50dBm with spectrum analyzer. I will connect radio -> direction coupler -> antenna, and coupling port -> 2W 30dB attenuator -> SA? I cannot find this information on minicircuits site (I have ZFDC-20-4 20db 1GHz coupler). Thanks for great videos
The maximum input power is listed in the datasheet. For 1-10MHz, the maximum input power is 0.5W (27dBm), and for 10-1000MHz, the maximum input power is 2W (33dBm). So, unfortunately this coupler is not suitable for 40-50dBm input. For that kind of power level, you're much better off using an RF sampler.
@@w2aew Thank you
Is it possibile, when antenna is matched to 50ohm (checked using resistors bridge, antenna tunner and oscilloscope), that there is standing wave in antenna's feedline? (Asuming that coax is also 50ohm). I think that should not because whole system is matched so should be no reflectuons, but I am not sure if coax dimensions can introduce some reflections.
Ideally, if the 50 ohm coax is terminated in a 50 ohm load, there will be no standing waves. However, depending on the coax, small impedance discontinuities can be introduced by bending the coax, which can result in small reflections and small standing waves.
Hi Allen! Thank you for taking your time to make this excellent video! I have some questions. If I may! I now have a ZFDC 20-4 (which works for me and no -5 on eBay!) I am using a Rigol DSA815 w/Tracking Gen. From the D.C. I have the OUT going to the TG, the CPL to the SA and then with 0db i "Normalize" the TG. "Then" I attach a precision 50 ohm load to the "IN" port. I believe that this is the correct procedure to measure Return Loss. In this scenario, it appears I am seeing the R/L of the 50 ohm load. The freq start 1 MHz Stop Freq 1Ghz. Please correct my procedure if I am in error. Final question, what is the procedure for checking Directivity for the D.C. ? Thanks In advance Allen. 73's David K8KEM
In your procedure, you're using the "open" on the IN of hte D.C. to provide a 100% reflection in order to normalize the coupling factor of the D.C. This should work well enough. Then, connecting your 50 ohm load, you should see a very low (large negative number) return loss. To measure the directivity - connect the TG to the IN, SA to the CPL and 50 ohm to the OUT. You should get something that is about 20dB down (the coupling factor). You can "normalize" this trace, then swap the IN and OUT connections on the D.C., and what you see should be the directivity (about 27dB down). Directivity is the difference of the CPL response for forward and reverse signals.
w2aew again Thank you so very much Allen! I have learned so much from you! What makes your videos so great is that you speak clearly and quite distinctly and at a pace that is very good! 73's David K8KEM
Thnx ... very useful. I just received my reflection bridge and want to check my antenna's using the VNA. My reflection bridge has IN OUT and a DUT .... i should connect the antenna to DUT and the signal output of the tracking to IN. I don't quite understand your setup.
If you have a VNA, it would already have the bridge or directional coupler built in. There shouldn't be a need for an external reflection bridge (unless it is an older VNA that specifically used external bridges/couplers).
@@w2aew Interesting answer ... i have a HP 4195A .... how should i connect an antenna in that case?
@@egbertgroot2737 OK, that's an older analyzer that uses an external transmission/reflection test set. A directional coupler will sample the signal going thru the coupler from IN to OUT. Since the signal you want to measure is the reflection coming back from the antenna, you would want to connect the antenna to IN and the signal source to OUT. The manual for the HP4195A can be found here: literature.cdn.keysight.com/litweb/pdf/5950-2942.pdf?id=619880
@@w2aew Ah i understand! Very useful answer. I only have old equipment ;-) ..... thanks for your quick reply! Greetings from the Netherlands. Pe1JKU
Thank you for another great video. At about 6:40, you switch the load from 50ohm to 1M ohm and comment that almost all the power is now reflected. On the scope, indeed I see both the yellow voltage trace and the yellow rms voltage readout go from around 225V to 407mV, the result of the two signals adding together. FB. And I can see the blue trace showing the coupled reflected signal.
My questions: Why is the coupled signal phase shifted (about 45degrees), why isn’t the main line voltage shifted some too?
The main line isn't shifted, because the scope is triggering on that line (so it always lines up in the same place on the screen). The phase shift of the reflected signal in this case is simply due to the propagation delay back and forth through the coax.
question ,i have zfdc 20-2000mhz, with 0dbm connected to output and in open, cpl line=-20 all good, total reflection,with perfect termination
when i terminate with dummy load i get -45dbm thats. 25 down on an open, very good. Thing is when i connect and tune my antenna i get -55dbm, how can the antenna be better than a perfect load. cable and generator all 50 ohm
Alan,
A very informative video per usual but -- and forgive me if I sound grumpy -- it would be great if you could do more stuff for us proles who limp along with a test equipment budget several magnitudes less than yours. For example, your time domain refectometry stuff was a tour de force and scintillating because it had "everyham" written all over it.
Most of us are lucky if we have An old 465 and an AN/URM-25D and some grotty RG-8X.
Respectfully,
Willie, the Grouch.
Understood Will. Of course you could manually sweep the return loss with a directional coupler and a scope and signal generator. But, I wanted to focus more on the coupler rather than the manual process with this video. So some videos will involve more extensive equipment, some won't. Thanks for watching, and for your comments.
*****
I completely understand. Thank you for your response. I think I need to get a grip and realize that you are doing this on your own time, out of the kindness of your heart, and I am essentially getting this content for free.
Was having a bad hair day. Please keep up the good work!
William Phinizy No problem Will! I am lucky that I have access to some really cool tools due to my job. Hopefully I'm striking a good balance between my hobbyist and professional viewers. Thanks again for watching!
automatic power control loop for Automatic gain control ??
Interesting,
Brilliant....i think .if anyone can explain it you can