NanoVNA V2 own build with the results


Erik Kaashoek
 

This post is somewhat off topic but I am so happy with what I achieved I felt I earned some bragging rights

For those that need a nanoVNA V2 for tuning their 2GHz antennas there is no real reason to wait.
If you have a close look at the attached picture you will notice the main nanoVNA V2 components in a home build.
In the middle back-to-back are two ADF4351 modules. On top of the aluminium bar on the left is the 0.1MHz till 3GHz bridge and on the right is a PCB with three IAM81008 mixers dead-bug style. All controlled by an Arduino zero hiding at the top. Audio goes to a line in of a PC and that is all you need for a GHz VNA.
With this home build VNA I was able to solve a problem of my home build 2GHz Spectrum Analyzer that is hiding underneath the VNA.
The aluminium bar at the bottom of the picture is actually a 5 resonator interdigital cavity filter. I have been trying to buy one for a long time but as I wanted to convert the 2GHz first IF of the SA directly to the second IF at 10.7MHz I was not able to find one narrow enough and finally decided to build it myself.
So I first had to build the 35MHz till 3GHz VNA, just like the NanoVNA V2 (although not so portable)
The construction of the cavity filter proved to be doable without any special tools except a 4mm tap. The aluminium bar for the housing and the copper rods for the resonators can be bought cheaply per meter.
Tuning the cavity filter proved to be more difficult than expected as there is absolutely nothing that gets thru if out of tune. So I used a simple trick that is of interest only for people that want to build their own cavity filter and now it works!
Center frequency 2019MHz, 2dB bandwith 4MHz. Better than -70dB at 10MHz offset. Passband attenuation is -7dB
The spectrum analyzer has hardware RBW filters at 300kHz and 30kHz (top tin box at right) and a log amplifier (top tin box at left) and variable FFT stitching RBW filters to a minimum resolution of 1Hz. IIP3 is +17dBm and noise floor at 300kHz BW is around -100dBm.
To prove it is working I added a 0 to 1GHz scan of the spectrum around my house using a small antenna. You will notice the FM and DAB transmitters and the rather strong cell phone base stations
Again apologies for the off topic post.

Erik, PD0EK

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