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- Опубликовано: 19 май 2024
- This video shows how to setup your NanoVNA to measure coax loss using an S21 measurement on a VNA. I show the setup and calibration process, as well as some actual measurements of a few lengths of RG-174 and RG-316 coax that I use for my portable (POTA) HF operating. More info on the custom NanoVNA stand here:
forums.qrz.com/index.php?thre...
00:00 Introduction
00:18 Credit and Inspiration for the video
00:54 Coax samples to be measured
01:24 Hardware setup for calibration and measurements
02:55 Setting up the frequency range
03:23 Running the Calibration
05:03 Setting up the Traces and Markers
06:54 Making the loss measurements on the samples of coax
09:28 Summary
10:39 Thanks given for the NanoVNA stand 
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Alan, Thank you for the shout-out, I appreciate it. You have given so much to the Ham Radio/Electronics community that when I saw that you had a NanoVNA I thought I would send you one of my stands as a way to give back slightly. I'm glad that you're using it and finding it useful. 73, and keep up the great work!
The stand you designed and made is fantastic. I'll order one soon for my birthday!
Great video - as usual. The importance of including any necessary connection adaptors when calibrating VNAs is generally not properly appreciated. While it's OK to ignore them at HF, failing to do this at VHF and upwards, especially if trying to measure phase, can be very misleading.
Thank you for your very concise tutorial.
When checking cables it is a good idea to leave S11 enabled. This is the best way to spot any problems. At these frequencies, anything over -30dB should arouse suspicions,
I just want to say without people like you sharing what you know is a gift thank you.
Love the nano VNA. Your demonstration was excellent.
I'm getting a Nano VNA soon so I'm glad you put this. Great little stand also. Have a great Christmas and New Year!
Great Vid, Very clear explanation and very useful , Thanks
Awesome, really a cool VNA stand.
Compliments ❤ This is the best channel for Electronics Enthousiasts... Thank you!
I've watched quite a few videos on the NanoVNA (and H4 in particular), and setting it up, what it can do, measuring loss, SWR, etc. but none of them showed the process from start to finish like you have. And markers!!! - Thank you, that's really really useful for a quick check on both loss and SWR for specific frequencies within the range. Really appreciated and subscription added.
Excellent training video, thanks for sharing your experience.
Many thanks for your in depth video. Very grateful you are sharing you knowledge with a hobbyist such as me. Have a great Christmas and a Happy New Year.
Very informative Alan, thank you for sharing. I always enjoy your videos
Best video so far on testing coax.
Lots of thanks Alan. Your video is very informative and useful.
Spot on info, very well explained thanks.
Great video! I like the 3d printed stand too. Thank you for sharing.
Very cool! I recall looking at the frequency-dependent loss effects on rise time for some 25' and 50' RG-58 (and Bil Herd mentioning pre-emphasis to counter that in high-speed PCB-based applications). Now I'm inspired to go measure those same cables on a VNA. It looks like the insertion loss directly shows you the frequency effects. :)
That was a good point during the calibration, to zero out the adapters
Thanks for another quality video!
i like those nanovna instructions, thanks
Thank you for the tutorial it's a great video.👍
Thank you, Alan.
It's good to know those thin cables ain't that bad. :-)
Hey Alan!!
Just worked you ground wave on 20 meter CW from my QTH in Montague to your POTA station at Jenny Jump State Forest!😀👍
Fantastic when I’m able to work ground wave close by!
73 de N1XV
Montague, NJ
thanks fir working me! This was my first time at K-4995. I was near the observatory, nice 1000’ elevation there.
Thanks for yet another informative video! Additionally, we can look up the corresponding data sheet for the expected typical numbers. Those of course don't include the losses in the connectors. About the nanoVNA standard. I was also thinking about something similar, but rather to take the stress of the device connectors and use some chassis mount for the "outside world". Until that time am just very careful with it, as I also see you too, especially when the adapter is getting longer!
Merry Christmas, Alan.
Hello, thank you, I will check my cables with your instructions!
brilliant! spot on and very informative..
Great video Alan! This makes measuring coax loss much less intimidating to me. Merry Christmas! KF4LMZ
Merry Christmas and Happy Holidays to you.
So glad ... Thank you alan
Good job! I like all your videos
Very informative Alan, thanks. I'll have to go test some of my Amazon-purchased RG-316 cables. I also frequently join a pair of 25' cables with a BNC barrel, so curious to see what the total loss is and if it is better to just use a single 50' cable for example.
Good stuff!Thanks.
I usually use a wattmeter and dummy load on the end of the coax. Have to admit the vna looks like more fun.
Thank you! This is just what I wanted to do. I had some RG174 but recent got some RG316 this past year. I was curious what the losses are between the different cables and some different lengths. I'll try measuring mine this week.
Appreciated.
great!
👍Thank you sir.
Good luck!
To accommodate for connectors, pigtails etc. which I have to use during calibration and not using after the calibration I use option "electric delay". As far I remember this option is available in Dislord's version of nanoVNA firmware.
Merry Christmas! 73!
The electrical delay will ONLY account for the additional phase/delay by moving the reference plane. It will NOT account for the LOSS or impedance discontinuities in the adapters, pigtails, etc. as electrical length adjustment assumes a perfect lossless 50 impedance along the length that is added/removed with the electrical length adjustment.
@@w2aew Good point - thank You.
This is timely as I want to measure my RG58 coax loss.
They shouldn't be too bad with three about 20' to 25' for five attic dipoles for 20m to 10m and one at about 60' for 60m. Coax data shows they should be around 0.6 dB so It'll be interesting to see.
If I buy coax now I want to see the braid as I bought one length which is very poorly screened, I don't want any more of that. Perhaps the best thing for that would be strip out the braid and bury it for an earth.
G4GHB.
Thank you for the tutorial it's a great video.
What would be the disadvantage of just doing a thru cal only with your known good shorting cable?
Could be also need to push the frequency up and see where the cable links drop a 3db loss.
When measuring very low loss devices like this, every little thing (such as the source match) matters, so it makes sense to do the OSL calibrations also.
Thanks! 👍 And Merry Christmas!
Thanks for yet another piece of good info.
I have a question: Does it make sense to measure coax signal attenuation as 1/2 of return loss with single port and the length of coax shorted/open at the end. How bad would it be compared to S21 measurement you have shown?
You can, but.... ...you won't be able to tell if the cable has a break or short somewhere along its length, or a bad connector at the far end.
@@w2aew Merry Christmas and thanks for the reply. The use case would be: a "found in the attic/cheap on a hamfest" roll of coax with no connectors and me be willing to sacrifice one good connector. A short/break could be detected using TDR.
@@Piotr_P_MSounds like a plan. Also, check out my video on measuring the impedance of unknown coax...
I was going to ask you about that stand, and then you threw it in at the end there. :-)
See the link in the video description.
Got it...
Hi Alan , big fan, any chance of you doing a video on testing dynamic and power microphones with a CRT oscilloscope ? Or even better your procedure for testing microphones.
Peacen73FromOZ 🇦🇺
Love it! I wonder why yhe Nano VNA comes with an OSL cal kit, when the $30k Field Fox at work doesn't.
Because the NanoVNA cal kit is FAR from being a high quality "standard" - albeit sufficient for hobby use.
@@w2aew @w2aew I understand your point; however, if a low-quality VNA can come packaged with a low-quality standard, a high-quality VNA could easily include a high-quality cal kit. We'd pay to avoid worrying about what else we need to purchase. I reckon I could be oversimplifying with that logic, but it becomes tiresome getting nickled and dimed for an item necessary to perform functions that are installed options on the instrument.
@@ernieschatz3783 The other problem is that the type and gender of the connectors on the cal kit in professional applications are typically purchased to match the DUT - and given the wide variety of DUT types and connections, it wouldn't be practical to include a kit with the instrument - and thus it is left to the user to select the cal kit that best suits their needs.
But let's face it, the main reason is that companies like Keysight want to make as much profit as possible. A decent quality manual cal kit probably costs them a couple hundred bucks. They know they can sell that to you for much more as a separate item. They mainly sell to "big business" where this sort of practice is considered the norm so they get away with it. Until purchasing managers start demanding better value for money they'll keep on doing it. Sad but true.
@@Chris-hy6jy Yeah, in all fairness, I think if I was employed by a test equipment maker this would just be an accepted norm that's had decades to normalize, but offering a packaged deal with perhaps the most common form of OSL would be a very helpful improvement.
Very nice, the "through" adds some delay though, it should have been in the loop for calibration of ch0 or ch1 shouldnt it.
Yes, but since I wasn't measuring (and didn't care about) phase or prop delay, I wasn't concerned about it. It only needs to be part of cal when you want an accurate phase or group delay on the thru measurement (or need to establish the calibration reference plane at some DUT interface).
@@w2aewis there a book you can recommend on such accurate measurements? Thanks and merry Christmas!
@@keylanoslokj1806 There are probably good books that I am not aware of. but there is good information here:
coppermountaintech.com/introduction-to-the-metrology-of-vna-measurement/
and
www.mwrf.com/technologies/test-measurement/article/21849791/copper-mountain-technologies-make-accurate-impedance-measurements-using-a-vna
Thanks for the video. It’s as well done and informative as always. On the subject of coax, I’ve come across a few videos that preach building coax cables to quarter wavelengths of the frequencies that it will be used . How critical is this? Some of the videos make it sound like if this practice isn’t followed, the signal will be so degraded that it’s pointless to use the coax.
Your video seems to prove the opposite without even trying. I defer to wisdom .
Also, is the stand your vna is in self printed or retail?? If you’re selling them, where do I sign up?
Also, I purchased an RF field strength meter that is less than advertised. Is there anyway I can email you a picture of the innards of it ? I’d like a more experienced opinion. Thanks.
Cutting coax to one quarter wavelength does nothing special other than invert the load impedance around the coax impedance. It makes a high impedance load look like a low impedance and vice versa. For a well matched load, the length does not matter. When the coax becomes part of the antenna, particularly part of the counterpoise, then a quarter wave line will form a tuned counterpoise.
C.B.'ers seem obsessed with trimming coax inch by inch to ½λ. They don't back down when I say why not the jumper lead from the tx to SWR meter too? They say it must be 3', 6', 9' or multiples of 3' but not carefully trimmed. Or that both coax cables are connected together by the SWR meter to form one cable so all their trimming is wasted.
I agree with W2AEV, if the aerial is not tuned properly the coax acts like a counterpoise earth. I think this is where the myth of trimming coax came from, they say the ½λ coax is the same impedance and has to match the tx and aerial for the least loss. No coax manufacturer states that.
I've only seen one video where an amateur says it does matter.
G4GHB.
👍❤
Alan amca harikasın yarın nasipse ilk isim 7mhz de koaksiyel kablomun. Kayıp oranına bakacağım inşallah düşük db çıkar sonuç ❤
I like how you built a stand for your nano VNA. How can I can get the stand you have for my nano VNA to do testing on Common Mode Chokes.
Did you watch the video to the end? I put some details on the source of this at the end of the video, as well as a link in the video description.
@@w2aew I missed it and thank you.
Any chance the STL files for the end pieces for your Nanovna are available on line someplace if someone wanted to 3d print their own set?
Could be. I didn't design it. Check the link in the video description.
Great video, is it possible to print out a hard copy on a computer / printer? Thank
There is a PC application for the NanoVNA which can be used for that.
Thank you
Why didn't you use the Measure/Cable option? S11 is enough, by which we can measure the attenuation of a coax whose other end is distant. There we also have information about the length of the coax, and its impedance.
That is an option (if the firmware supports it). Of course, a break in the cable would only be detected if the measured length differs from the actual length (if known). You'd also have to check from both ends to be sure that both connectors are good.
Hi Alan, have you tried using LibreVNA?
No, I never used one.
Whether it is possible to measure the velicity factor
by NanoVna?
Sure - ratio of measured length to the actual length.
Is it possible to measure the loss on an installed cable in which case you don't have access to both sides of it?
Alan, may I ask you to talk about OpAmp "double T" ressonator? I am not sure if "double T" is the right way to say it in English...
I made a search and found about Twin T resonator. Is it a good subject for a video? Thanks anyway.
That looks like it might be an interesting topic - I'll add it to my list.
@@w2aew amazing!!!! Thank you for considering it. Have fun.
Isn’t the open the same as nothing on the connector? I gladly give up that minimal loss for the compactness of the coax both size and weight.
At HF frequencies, yes, because the wavelength is relatively long compared to the adapter dimensions. But, the "open" cap does help to prevent stray signals from coupling into the port. As frequencies get higher where the wavelength becomes shorter, it is important for the physical/electrical location of the open, short and load to *match* so that the phase lines up, which is why there is an "open" standard.
Where can I find the file for the 3D printed stand? Thanks
I don’t know. Try Google.
shouldn't you be doing the calibration with the standards on the far end of the co-ax you are testing?
No, because then the loss of the cable will be removed from the measurement.
2db is 37% power loss, right? Is that acceptable? I guess it depends on what you are doing and what you are willing to accept. Personally, I think that's pretty high.
Correct. It depends on the application whether 37% power loss is ok. In typical amateur radio applications, 2dB would not even be noticeable.
what is an s unit please ?
On most ham radio receivers and many shortwave radios, there is a received signal strength meter. Most are calibrated to show a -73dBm signal at S9, and each S-unit on the meter corresponds to roughly 6dB signal strength change.
@@w2aew nice to know, thank you so much. does it have any specific meaning, does one S unit represent something special or is it for convenience ?
@@AboubakrA Just a convenience. S9 = ~ -73dBm, S8 = ~ -79dBm, etc. Just a way of "grading" the strength of the received signal.
some ............... use fiber optic cable instead of coax Sir so no ................. measurement
Pat W5WTH. Warp speed, man. Thanks Alan for teaching me something new. I was able to check the coax I repaired after the dog ate it. Come to find out my repair was a good one!
Video making two new ones…
The dog ate my coax! RG-316 BNC with ferrite beads. Make two for the cost of one!
ruclips.net/video/N8Fb6DMuwIU/видео.html