How Long Is Your Coax? Testing with NanoVNA

[@kensejkora4424]

Great video, Hayden. On many of the newer firmware versions (latest for the SAA-2N is v1.3.31 dated ~18-Jun-2024) there is actually a feature to directly measure the cable length. After you turn on the NanoVNA, invoke the menu, select 'Back' (if necessary), then select 'Measure', and then select 'Cable (S11)'. After you enter the velocity factor in percent, the display will show the cable information such as the characteristic impedance, length in meters, and return loss. Also, you can select more sampling points to improve resolution, such as 401 points vs 101 points. This is accessible under the 'Stimulus' menu as 'Sweep Points'. Again, great video. 73 Ken -- WBØOCV

[@HamRadioDX]

Thanks mate! Sounds like the next video will be - updating a NanoVNA firmware :) Cheers I'll give it a go!

[@HamRadioDX]

I did the firmware update tonight, that's fantastic mate! Works well 👍

[@HamRadioDX]

One question though is that if I measure the Cable length and enter the VF, such as 86% it shows the length as 617mm... (for a 6m length of cable) if I enter 860% on the VF, then it comes up as 6.17m. Perhaps I have something strange happening in my calibration or something

[@HamRadioDX]

Ah I had it on an old frequency range for another test I was doing... when changing the range it changes the length calculations. For the direct cable measurement do you need to do a calibration first over the selected range?

[@kensejkora4424]

@@HamRadioDX Great point, Hayden. From what I've heard, read, and experienced, the best results are obtained if the calibration used covers a frequency range where the approximate lenght of coax corresponds to a wavelength of between 1/4 and 1 wavelength. Thus if you think your coax is somewhere in the range of 10 to 30 meters in length, you might set your stiumulus range from 10 MHz (~ 1 full wavelength at 30 meters) to 100 MHz (~1/4 wavelength at 10 meters). For a shorter cable of a few meters, you might want to set the stimulus bounds from something like 30 MHz to 300 MHz. If the display shows at least one phase shift on the S11 phase trace as indicated by a vertical line on the trace indicating a 180° shift, but less than 3 or 4, you are covering the correct frequency span. Also, I think I read somewhere that you don't need to have a valid SOLT (Short, Open, Load, Through) calibration to measure cable length, as long as the stimulus range overlaps at least one phase change in the S11 phase trace.

[@mandytuning]

Best 5min of any nanovna video. Simple and straight to the point without crazy formulas.

[@jez4491]

Always nice to see ways to use the nanoVNA.

[@HamRadioDX]

I haven't used mine nearly enough - but it was great to be able to use it for a few projects recently

[@FEPLabsRadio]

I knew it could do that, I've never done it on the nano though. Good work mate!

[@HamRadioDX]

Thanks Jim!

[@mikeb2737]

Hayden, this is great stuff. I actually use an Anritsu S412E at work. I am also S412E certified and ETA line and antenna sweep certified. I use my VNA and S4401A quite a bit but don’t know all of its capabilities. Thanks again. Mike. AF4AY

[@HamRadioDX]

That Anritsu looks like a nice piece of kit! Thanks mate

[@wespurdy1437]

This is really helpful. I recently installed a cable through my roof from a large roll and cut off the end and installed a plug. But I have no idea how much cable I used. I will now use this to find out, thanks 👍

[@HamRadioDX]

Nice work! Glad it helped

[@yv6eda]

Great info Hayden! Thanks!

[@yetiradiovk4yt]

Excellent video mate. I have a VNA but don’t fully understand its many features.

[@HamRadioDX]

Me neither! I'm still learning!

[@newYorkStories]

Amazing tutorial. Thank you!

[@HamRadioDX]

Glad it was helpful!

[@Davidm-M0TPT]

You can also use the numbers on the jacked of the coax and subtract one from the other :)

[@HamRadioDX]

Some cables don't have the distance markings on them. Others are installed in place and you can't see/get to them.

[@DonzLockz]

Very cool, good to know.👍

[@HamRadioDX]

Thanks 👍

[@hugov392]

It's pronounced "ess one one" not "ess elevent". The numbers are indices in a 2x2 matrix.

[@randykitchleburger2780]

It's pronounced ess the ese Nhutts

[@mikeb2737]

Who are you? The ess police. 😂

[@bitemykrank1970]

And in the time you took to set up the VNA, and " guesstimate " your cable length, Myself, with no help from anyone, and using a simple tape measure not only measured 10 seperate cables, but I even managed to put the antenna's back up in the air aswell.

[@HamRadioDX]

All the power to you then

[@WaschyNumber1]

Hello I'm new to HAM and learning, I would like to ask how long can a cable be, for testing for example a nanovna to the radio or to a antenna, I mean if it can't be direct connected on the radio or antenna and so on, becourse of space reason on the devices, please ?

[@DGrdan-m9t]

Hi, Is it possible to measure the length of the 75ohm cable, rg6 or rg11?

[@DreadMakerRoberts]

Challenge. I have a co-axial cable connected to an antenna wire. If I know the velocity factor of the wire can I have the vna read from the connector at the antenna to its final length to get the wire length?

[@mandytuning]

Have to disconnect both sides

[@ashemoski]

I can't believe it took me 2.5. minutes to realize that Nano has N connectors! (When you mentioned "the SMA version...") 😳

[@HamRadioDX]

I think this one has extended range over the SMA NanoVNA’s too!

[@forgetyourlife]

When I look up velocity factor for rg-8x every manufacturer has a different percentage.

[@Penfold42]

How much does a good or poor calibration impact the measurement ?

[@RobB_VK6ES]

If you want to improve resolution calibrate the VNA, only calibrate over the expected range of frequencies rather than the full 3GHz. 101 points over 3GHz is very sparse. The VNA simply interpolates between the 101 calibrated points leading to a false sense of measurement confidence.

[@gregwmanning]

I need to get a two port device, I wonder if this is it?

[@kn6vbw]

Next video would be good to learn how to find the velocity factor of your cable; since the same type of cable will be different between manufacturers and even batches, for the no name wholesalers.

[@mandytuning]

If you know the exact measurements of the cable, just change the velocity factor until readings matches the length of your cable. i did it and you will be surprised the difference from amazon rg8x vs abr rg8x. 2 sets of abr was spot-on 82%. 2set of Amazon 66%.

[@martinpe9tig]

never seen a vna with N connector ... mostley sma... never heard a new invention ...measuring tape? 😁 🤣😂

[@HamRadioDX]

NanoVNA SAA-2N

[@michaelross-aj6fgvk3rz]

Often coax cannot be measured with a tape measure because it is installed up a tower, or inside a roof or on a large roll.