Nanovna for antenna tuning

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Polecat
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Nanovna for antenna tuning

Post by Polecat » Mon Mar 23, 2020 1:30 pm

I bought one of these on ebay and used it to tune an antenna with great success.

If you're just starting out like me, I thought you might appreciate a few pointers. And if you're an engineer reading this, feel free to jump in and modify if you think it's necessary.

Most of the YouTube tutorials make it seem more complex than it actually is.
This was the best I found:

Even then, I went through some trial and error before I got the hang of it. Once you understand the process, it takes about 5 minutes to calibrate the machine and test an antenna.

First I'd get hold of a touch screen stylus - this unit is ridiculously small!

Next, hide 'Trace 1' and 'Trace 3' so you only show SWR and Impedence (Trace 0 and 2).

Then select the frequency band you're testing. I started with 5 MHZ either side of the frequency I was tuning to.

Now go through the calibration process per YouTube using the different plugs.

You're all set. Plug in your antenna (you need an sma adaptor on your antenna plug) and read SWR and Impedence levels across the curve.

That's it.

One question for the engineers: unlike an SWR meter, this unit tests the antenna in isolation from the transmitter. Can different power levels alter the SWR performance of an antenna?Image
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Re: Nanovna for antenna tuning

Post by Polecat » Mon Mar 23, 2020 8:01 pm

£35 well spent!
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Re: Nanovna for antenna tuning

Post by Albert H » Tue Mar 24, 2020 3:00 am

No - SWR is the same irrespective of power level. That's why I'd always do a final test of an install with a 1 Watt test rig with a built-in Breune SWR bridge - it saved expensive mistakes!

Where did you get the NanoVNA?
"Why is my rig humming?"
"Because it doesn't know the words!"
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Re: Nanovna for antenna tuning

Post by Polecat » Tue Mar 24, 2020 5:28 am

Thanks Albert.

This is the item:

https://www.ebay.co.uk/itm/223937847319
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Re: Nanovna for antenna tuning

Post by teckniqs » Tue Mar 24, 2020 6:46 am

Only 26.99 here: https://www.ebay.co.uk/itm//333443934775

....Been told they are no good because "they only have a dynamic range of around 35dB"

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Re: RE: Re: Nanovna for antenna tuning

Post by Polecat » Tue Mar 24, 2020 7:25 am

I saw quite a range of prices Teckniqs. That one says it excludes battery(?). Also delivery times vary greatly. Mine arrived in 5 days. Some also come with a plastic storage box but mine didn't. You pay your money and take your choice!

The spec states 70db up to 300mhz. 50db at 900mhz. Hope that helps.
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Re: RE: Re: Nanovna for antenna tuning

Post by teckniqs » Tue Mar 24, 2020 11:41 am

Polecat wrote:
Tue Mar 24, 2020 7:25 am
I saw quite a range of prices Teckniqs. That one says it excludes battery(?). Also delivery times vary greatly. Mine arrived in 5 days. Some also come with a plastic storage box but mine didn't. You pay your money and take your choice!

The spec states 70db up to 300mhz. 50db at 900mhz. Hope that helps.
Fair enough and plus your one came from the UK, so a LOT less time to arrive...

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Re: Nanovna for antenna tuning

Post by Polecat » Tue Mar 24, 2020 1:38 pm

Impatient is my middle name so speedy delivery was the main decision factor.

Next up - testing for spurious emissions and harmonics across 3 different rigs (2 Chinese with different chips and 1 Brit) with a £30 SDR which is in the post.

And then repeating that test on a 1w QN8007 chip based xmitter, also in the post. It's meant to be the cleanest of the all in one chips ie the cream of the crap. We'll see.

And finally, range comparison of a 300ohm Ladder Line Slim Jim antenna and a 450ohm version which has yet to be built.

I'm not one to stay at home for 5 mins but in the current situation, it provides ample time for RF exploration and hopefully, learning.

Stay safe!
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Re: Nanovna for antenna tuning

Post by teckniqs » Wed Mar 25, 2020 8:53 am

Don't ever use SDR's as a specrum analyer, they are terrible and create their own images and sproggs.

....The very worst possible thing you could ever use as one...

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Re: RE: Re: Nanovna for antenna tuning

Post by Polecat » Wed Mar 25, 2020 10:09 am

teckniqs wrote:Don't ever use SDR's as a specrum analyer, they are terrible and create their own images and sproggs.

....The very worst possible thing you could ever use as one...
Funny you should say that Teckniqs!

The SDR arrived last night and I did a quick test of a 500mw chinese box. The results were even more shocking than I expected. There were 5 massive spurs +/- 5mhz of the transmission frequency and the same at the 2nd and 3rd harmonic frequencies.

I knew something was wrong because my FM receiver is quite sensitive and it wasn't picking anything up on the spur frequencies indicated on the sdr.

I've done some reading and looks like the sdr gets overwhelmed by the proximity of the signal. Is that your understanding?

And if so, can't I just attenuate the tx signal or else take the SDR out in the car? What do you reckon?
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Re: Nanovna for antenna tuning

Post by Polecat » Thu Mar 26, 2020 11:41 am

@teckniqs

Correction to my prior post on the SDR dynamic range. For some reason I posted the spec for the NanoVNA. Doh.

You were right about 35db. But a software update in 2017 improved it to 50db. Not great but useable.

I'll start a new topic on the SDR when I've done some more experimentation.
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Re: Nanovna for antenna tuning

Post by biggiedan » Thu Mar 26, 2020 5:28 pm

I think the V2 is a little better.

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Re: RE: Re: Nanovna for antenna tuning

Post by Polecat » Thu Mar 26, 2020 7:40 pm

biggiedan wrote:I think the V2 is a little better.
Hi Biggiedan. Yes the NanoVNA v2 has a wider frequency range but does it do anything better in Band 2? Difficult to see what could be better tbh....
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Re: Nanovna for antenna tuning

Post by ronald001 » Thu Apr 09, 2020 10:23 am

Got one myself, great little device!

search for NanoVNA saver - it's great PC software which makes things a lot easier!

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Re: Nanovna for antenna tuning

Post by Polecat » Thu Apr 09, 2020 11:09 am

Thanks Ronald. I will.
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Re: Nanovna for antenna tuning

Post by Polecat » Thu Apr 09, 2020 8:48 pm

Downloaded it and yes, makes a huge difference to the experience. Thanks a lot!
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Re: Nanovna for antenna tuning

Post by ronald001 » Thu Apr 09, 2020 9:33 pm

You're welcome - glad i could help ✌️

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