Tuning a Duplexer with NanoVNA V2 PLUS4 Vector Network Analyzer

[TXFitz]

Total noob here that is interested in setting up a low powered neighborhood GMRS repeater and would like to know if the NanoVNA would be a good low cost tool to tune a duplexer. I want to build the repeater myself to learn and don't mind spending a bit to get tools I can use. Is the NanoVNA a good choice or is there a better choice for entry level low cost tool? Thanks.

 

[Ubbe]

Any VNA that can show a frequency spectrum live while you tune the duplexer will do. Get a duplexer from Ebay that covers the frequencies and set the RX part to attenuate the TX frequency and the TX part to attenuate the RX, and at the same time with as little loss as possible for its own frequency. But you always need to fine tune with the RX and TX activated and generate a weak signal from the antenna and tune for best reception and max output power. A transmitting mobile radio connected to a dummy load far away from the basestation but closer to the antenna can be used. You can listen in a radio or scanner tuned to the TX frequency to hear how the reception are while tuning the duplexer.

/Ubbe

 

[prcguy]

I have a Nano VNA and a bunch of duplexers and I'll see how it works in the near future. I've used the Nano to tune other things but its dynamic range might not be enough to get a duplexer perfect. The last mobile duplexer I tune had notches in the 75dB range and that may be the limit of the Nano VNA. Its good to have at least 10dB more range in the analyzer than the device under test has to measure.

 

[AB5ID]

Give these videos a watch:
#334: How to tune a duplexer with a NanoVNA V2plus4 | is it possible? - YouTube

#318: NanoVNA comparison measuring a duplexer - NanoVNA-H4 and SAA-2N - YouTube

#270: Tune a Duplexer with a Spectrum Analyzer + Tracking Gen or VNA - YouTube

 

[prcguy]

I just spent a frustrating 30min with my Nano VNA trying to get it calibrated and gave up and did an uncalibrated sweep of one notch on a flat pack 6 cavity notch duplexer. I came close to just smashing the VNA with a hammer and tossing it. In my humble opinion I think its probably ok for rough testing a duplexer but with its 1 second sweep time it would push me over the edge trying to tune something and I would smash it. To tune something you would have to make a small adjustment then wait for the slow sweep then find you went too far then adjust again and wait and oops too far the other way and keep doing that until you go lucky. Not my idea of fun.

Not to mention needing strong reading glasses to see the display and the push buttons will kill your fingers after awhile or your fingers might be too fat to use the touch screen feature. These things were apparently designed to be used by very small people with excellent eyesight and lots of time on their hands.

This duplexer was previously tuned with an HP/Agilent spectrum analyzer with tracking generator and it tuned up nice and fast with about 75 to 76dB notches and low insertion loss. The uncal connected through trace on the Nano thing was about -2.9dB so the marker at -79.45dB for one of the duplexer notches is in the ball park. I just noticed the marker was at 462.7MHz and this duplexer was tuned for 462.6MHz, so the notch appears to be in about the right spot.

I've never had a problem with the accuracy of my Nano VNA but it can be a frustrating POS when you need to test somethign quickly. If you want to tune duplexers get the right tool which is a quality spectrum analyzer with tracking generator or a scalar or vector network analyzer with proper cables and cal kits.

 

[Ubbe]

I use a VNA connected to a laptop and its resolution can be changed to allow quick sweep times. I would not use its own display that also makes it more difficult to save results and have bad user input management like touch display or minimal buttons. Look for one that can be fully PC controlled. (Can't all of them be PC controlled and the display are just an add on?)

/Ubbe

 

[TXFitz]

Thanks all. What VNA models do y'all suggest? Alternatively, what models of spectrum analyzers and tracking generators would be recommended? Or a vector network analyzer? I can see this will be another expensive hobby... but cheap hobbies aren't fun.