RF Coupler Testing

Did some dicking about with the VNA today and tested the rf coupler i built. Not sure how i interpret the data, but i have it LOL

 

The through port return loss. I figure what this means is from 1 to 100meg the through port has a quite flat frequency response.

Port Isolation. I figure what this means is i have a coupling factor of say -18db or near enough.  I might have to rebuild it with some more turns, I was looking for at least 30.

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!! This Is Serious Mum !!

Ok, it made RF before I broke it. Not a serious break, one of the trimmers failed and I cannot set the bias to the right hand bank. Going to be a bit of a job to pull it apart and remove the dead trimmer, thinking about it now, I really should have used SMD parts for everything that I could on the board to make fixing things like this easy. Will see how i go tomorrow when i dissemble it LOL

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Nano VNA

Ok, so these are my initial thoughts of the device. Firstly, the only issue I have so far is that Windows does not always detect the USB device. I am not sure exactly what the issue is, low voltage, USB drivers kind of flaky or what. But powering it from an external 5v supply the device turns on every time. So i think its windows and computer related, not the device.

On to testing. Not a lot of time today to do anything flash, so I ran a bunch of S11 measurements on things i had handy and the plots were as expected. I do not really have anything here to test in the upper frequency ranges, being a HF kind of guy, but on measurements up to say 100meg, where I have the ability already to compare against another tool, the measurements look legit to me.

First up, calibration is easy and it comes with open, short and 50ohm loads to calibrate to, apparently I have the 900meg firmware installed, if i can work out how to change that to use the 300meg firmware I will. I dont need to measure beyond a couple hundred meg at best anyway.

First up to be tested was the Tri-Band vertical. Yes it is poorly tuned LOL and the SWR plot is correct. LOL I need to fix that 😉

This is the smith chart for the tri bander.


And this is what the LCD screen is showing while testing the tri-bander.

Next cab off the rank was my home brew dummyload. I knew already it was good out to about 100meg, but did not think it would be fine out to 300. Guess i did ok with a handful of resistors LOL

Next up was a 70cm antenna off the MD380 DMR HT. Now i have no idea how accurate this is, but it looks like what you might expect to see with a dip where it is meant to be.

And this is what the device was displaying while testing.

All in all, so far for S11 measurements the nanovna has done exactly what it was designed to do. I was a little surprised that it is as accurate as it is. This is not a very expensive tool at all, like $90 Australian delivered from ebay. Add this in with the rest of my cheap test gear and I have a good selection of gear for not a lot of dollars. When i get some time I will do some 2 port measurements and see how it goes. I expect it will perform quiet well. Bring on the filter testing 🙂

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A New Linked Dipole

So for the longest time I have been using a Sotabeams linked dipole. Its been broken and repaired a number of times, but its getting to the end of its life. The links are more rust than metal, the centre has been broken and repaired a number of times and replaced, the coax and antenna wire has nicks in their sheaths. So rather than repair it or replace it, I decided it was time to build a new one from scratch. I have assembled the parts, RG316 coax, teflon wire and a sotabeams winder kit and parts. Will make it for 20, 40 and 80.

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