Beware of cheap underperforming clones

As of 2022 there are many badly performing clones on the market. V2/3GHz NanoVNA uses parts like ADF4350 and AD8342 which are costly and clones have been cutting costs by using salvaged or reject parts.

See official store and look for V2 Plus4/V2 Plus4 Pro versions only to avoid getting a bad clone. We have stopped selling V2.2 versions since October 2020, so all V2 hardware that are not Plus or Plus4 are not made by us and we can not guarantee performance.

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Saa2 output port attenuator


Stephen Laurence 2020/08/12 03:00

Perhaps a silly question from a retired doctor.......

On the output port, according to Gabriel’s circuit diagram on the bottom left hand corner, is a pi attenuator with 75ohm parralell resistors and 120ohm series.

This gives 14db attenuation of the output signal. I appreciate that its main function is to stabilise the output impedance seen by the DUT.

However I am more intersted in dynamic range rather than small imbalances to the connected devices. Would a reduction to 4db attenuation give a 10db increase of dynamic range? If I needed greater stablity of output impedance, an addition of an external 10 db attenuator would restore the original specification.

Steve L. G7PSZ

Stephen Laurence 2020/08/12 03:00

Perhaps a silly question from a retired doctor.......

On the output port, according to Gabriel’s circuit diagram on the bottom left hand corner, is a pi attenuator with 75ohm parralell resistors and 120ohm series.

This gives 14db attenuation of the output signal. I appreciate that its main function is to stabilise the output impedance seen by the DUT.

However I am more intersted in dynamic range rather than small imbalances to the connected devices. Would a reduction to 4db attenuation give a 10db increase of dynamic range? If I needed greater stablity of output impedance, an addition of an external 10 db attenuator would restore the original specification.

Steve L. G7PSZ

OwO 2020/08/12 18:04

Yes you can reduce the attenuation to improve the dynamic range, but the
receiver might saturate with a thru cable connected so you may need to
calibrate THRU with an external attenuator connected.

On 12/08/2020 18:00, Stephen Laurence wrote:

Stephen Laurence 2020/08/12 06:08

Thankyou.

So if I did change the input resistors to give 4db rather than 14db attenuation, I woud need a 10 db external attenuator to attach when required.

I was just about to add to my previous question by asking if a broadband low noise preamp of 10 or 20db in front of the receiver port would also improve dynamic range, but you have effectively answered my question. A preamp would also add a significant physical path/ time delay and presumably a 180 degree phase shift, both of which I suppose could be calibrated out.

The 4 inch screen version would however possibly have enough empty space to put it somewhere.

On a related subject, what is the input 1db (or .5db or .1db, depending on ones personal threshold) compression point of the v2 input? ( sorry if I have overlooked it in the wiki specs)?

Steve L

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