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NanoVNA suddenly got crazy measurements


Markus 2021/02/25 01:57

The device worked perfectly. But suddenly it began to deliver unrealistic measurement results.
It is a NanoVNA V2 plus 4 (FW: 20201013) from the official aliexpress store.

here are pictures of

1. reset all

2. reset all with 50 Ohm nonnected

3. reset all - calibrated and with 50 Ohm connected

Does anyone have any solution to fix the problem? maybe a bad solder joint?

Markus

OwO 2021/02/25 20:55

It's probably ESD damage to the port 1 RF switch (U801, MXD8641). You
can try resoldering the MCU (U303) to rule out soldering issues.

On 25/02/2021 17:57, Markus wrote:

Markus 2021/02/25 08:21

Thank you OwO.
I re-soldered U303 and U801 but nothing changed. same behavior as before.

how to prevent ESD damage in future?
i mean it is in a metal case and i always touch the vna with one hand the part of interest with the other when connecting it.
hat else should i do or not do?

thank you 4 your support!

OwO 2021/02/26 00:47

The switch itself is rated for 1000V human body model ESD, but the
problem is ESD through a transmission line that can transform the
impedance (either a charged transmission line or a discharge at the far
end of the transmission line). You can ask the seller to send you a few
MXD8641 for the repair.

Siegfried Jackstien 2021/02/26 13:26

just a guess ... could it also be a faulty 50 ohms load?!?

besides esd damage on the switch a defective 50 ohm load also would show
crazy results .. not?!?

greetz sigi dg9bfc

Am 25.02.2021 um 12:55 schrieb OwO:

Markus 2021/02/27 01:10

sigi this was my first thought too.
but the resistor is ok.

OwO is it a good way to go -> to short out all contacts before connecting?

John tf 2021/02/27 07:15

I got info on keeping from damaging antenna analyzers / RF test equipment yrs. ago , some of that was after repairing an analyzer .
1st off before connecting test gear to DUT Device Under Test , discharge before connecting - capacitors tester , antenna systems - ground / discharge any possible charge from RF , static etc.
Also for test gear just laying around , stray RF or static - I put 50 Ohm cal. loads on all test ports - while not being used .
You may be doing other work and forget that you your working on and putting RF or other energy's into the environment near sensitive test gear , antenna analyzers or nanoVNA etc.

KD0CAC

Jim Lux 2021/02/27 08:55

On 2/27/21 7:15 AM, John tf wrote:
> I got info on keeping from damaging antenna analyzers / RF test
> equipment yrs. ago , some of that was after repairing an analyzer .
> 1st off before connecting test gear to DUT Device Under Test ,
> discharge before connecting - capacitors tester , antenna systems -
> ground / discharge any possible charge from RF , static etc.
> Also for test gear just laying around , stray RF or static - I put 50
> Ohm cal. loads on all test ports - while not being used .
> You may be doing other work and forget that you your working on and
> putting RF or other energy's into the environment near sensitive test
> gear , antenna analyzers or nanoVNA etc.

This is also a decent reason to get yourself a bunch of those
antistatic  plastic connector covers (pink or otherwise) - they're
dissipative, not conductive. But at least when you pick it up after
shuffling your feed across the carpet on a dry day, the "zap" isn't
differential mode across the input.

John Cunliffe W7ZQ 2021/02/28 07:09

Try bending the inner conductor of the input socket together with a fine needle or exacto knife tip. I found they will lose reliable contact after a while. I actually went so far as to buy a couple of commercial grade and replaced the existing cheap ones. Had no problem since. Of course, the connectors cost me close to what the nano cost lol.

J.C.

Siegfried Jackstien 2021/03/01 00:27

Screw on port extenders.. If worn out.. Replace extender



Am 28.02.2021 16:09 schrieb John Cunliffe W7ZQ <n2nep@rochester.rr.com>:

> Try bending the inner conductor of the input socket together with a fine
needle or exacto knife tip. I found they will lose reliable contact after a
while. I actually went so far as to buy a couple of commercial grade and
replaced the existing cheap ones. Had no problem since. Of course, the
connectors cost me close to what the nano cost lol.
>
>
>
> J.C.



_._,_._,_

* * *

Markus 2021/03/25 04:30

HI OwO. I exchanged the MXD8641 and it is working again. thank you for the tip.

found the problem: one of a friends antenna was not connected to ground and the fiber pole of the vertical antenna is charged in the wind. i measured multi hundred volts at the antenna plug!

@ALL: Be carefull at unknown antennas. (or better at all antennas)

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