I've been my V2 Plus4 for antenna work for a couple of years. I've been careful but have a new setup with bias-tees in line.  I believe switching on/off the DC created a transient that blew the port 1.

Is there a fix?

I tried a full reset and calibration a number of times.  I just get big noise on the SWR trace with any 50 ohm load.

I repaired several V2.2, first version, not the V2 plus4. A 4-port RF
switch is directly at the input. I don't know for the plus4 version, but
most likely it has a switch too.
The switch is cheap and I bought a number of them via aliexpress. You
could contact nanorfe.com, they are the official seller of the V2
series. Also, the schematics of V2.2 can be found on their website.
Repair does require some skills and hot air tools since the chip has a
ground pad underneath. And a microscope comes in handy, the switch is tiny!

Reinier

Op 24-4-2024 om 18:52 schreef Lou W7HV via groups.io:

> I've been my V2 Plus4 for antenna work for a couple of years. I've
> been careful but have a new setup with bias-tees in line.  I believe
> switching on/off the DC created a transient that blew the port 1.
>
> Is there a fix?
>
> I tried a full reset and calibration a number of times.  I just get
> big noise on the SWR trace with any 50 ohm load.
>

Hi Reinier,

Thanks for the info.  I'll definitely look into that.  I've done a lot of electronics in the past, but am not equipped for dealing with these tiniest SMT devices.  I have a stereo microscope but not the hot air tools, so it might not make sense to obtain those just to try repair this device.

Lou

That’s one of the reasons I don’t use my nanoVNA for outdoor antenna
measurements. Dedicated antenna analyzers are much better protected from
this kind of damage.

On Sat, Apr 27, 2024 at 8:59 AM Lou W7HV via groups.io <louandzip=
yahoo.com@groups.io> wrote:

> Hi Reinier,
>
> Thanks for the info. I'll definitely look into that. I've done a lot of
> electronics in the past, but am not equipped for dealing with these tiniest
> SMT devices. I have a stereo microscope but not the hot air tools, so it
> might not make sense to obtain those just to try repair this device.
>
> Lou
>
>
>

Hi Reinier,

I looked into it a little more and it seems pretty straightforward to try.  I opened up my V2Plus4 and see easy access and lots of space around the the MXD8641, so I'm going to give it shot.  I ordered some chips, hot air tool, etc...  Coming from Aliexpress it'll probably take a couple of weeks to get everything.

This is an issue with this particular design, nothing to do with VNA
vs "antenna analyzer".

On Sun, 28 Apr 2024 at 08:28, Bob W0EG via groups.io
<morrisnc7=gmail.com@groups.io> wrote:

>
> That’s one of the reasons I don’t use my nanoVNA for outdoor antenna measurements. Dedicated antenna analyzers are much better protected from this kind of damage.
>
> On Sat, Apr 27, 2024 at 8:59 AM Lou W7HV via groups.io <louandzip=yahoo.com@groups.io> wrote:
>>
>> Hi Reinier,
>>
>> Thanks for the info. I'll definitely look into that. I've done a lot of electronics in the past, but am not equipped for dealing with these tiniest SMT devices. I have a stereo microscope but not the hot air tools, so it might not make sense to obtain those just to try repair this device.
>>
>> Lou
>
>

Unfortunately i needed to replace iC on my VNA also. The chip is extremly small and i have a lot of issues soldering it. Also the solder mask would withstand 2x resoldering.
Put 3dB attenuator im front of port 1 to protect it form ESD

Good luck! While you are repairing it, it may be a good moment to add an
ESD diode, e.g. the ESD101-B1-02. I wrote about it some years ago. It is
a tiny part which adds a just 0.1 pF. Did this for my old V2.2. At 1 GHz
totally harmless and if any, calibration will take out any effect.
Reinier

Op 28-4-2024 om 16:38 schreef Lou W7HV via groups.io:

> Hi Reinier,
>
> I looked into it a little more and it seems pretty straightforward to
> try.  I opened up my V2Plus4 and see easy access and lots of space
> around the the MXD8641, so I'm going to give it shot.  I ordered some
> chips, hot air tool, etc...  Coming from Aliexpress it'll probably
> take a couple of weeks to get everything.
>

On Sun, Apr 28, 2024 at 11:59 PM, Reinier Gerritsen wrote:

>
> ESD101-B1-02

Maybe I'll give that a try, but it is tiny.  The big package is 0.6x0.3mm.  Where did you place it?

Yes, I agree. The better antenna analyzers are essentially one-port VNAs.
The nanoVNA could use better front end protection. Perhaps consider keeping
3dB pads on the ports and give up a bit of dynamic range.

On Sun, Apr 28, 2024 at 10:59 PM Dragan Milivojevic via groups.io
<d.milivojevic=gmail.com@groups.io> wrote:

> This is an issue with this particular design, nothing to do with VNA
> vs "antenna analyzer".
>
> On Sun, 28 Apr 2024 at 08:28, Bob W0EG via groups.io
> <morrisnc7=gmail.com@groups.io> wrote:
> >
> > That’s one of the reasons I don’t use my nanoVNA for outdoor antenna
> measurements. Dedicated antenna analyzers are much better protected from
> this kind of damage.
> >
> > On Sat, Apr 27, 2024 at 8:59 AM Lou W7HV via groups.io <louandzip=
> yahoo.com@groups.io> wrote:
> >>
> >> Hi Reinier,
> >>
> >> Thanks for the info. I'll definitely look into that. I've done a lot
> of electronics in the past, but am not equipped for dealing with these
> tiniest SMT devices. I have a stereo microscope but not the hot air tools,
> so it might not make sense to obtain those just to try repair this device.
> >>
> >> Lou
> >
> >
>
>
>
>
>
>

directly at the input (between input and ground plane)

Op 29-4-2024 om 14:00 schreef Lou W7HV via groups.io:

> On Sun, Apr 28, 2024 at 11:59 PM, Reinier Gerritsen wrote:
>
> ESD101-B1-02
>
> Maybe I'll give that a try, but it is tiny.  The big package is
> 0.6x0.3mm.  Where did you place it?
>

On Mon, Apr 29, 2024 at 09:59 PM, Reinier Gerritsen wrote:

>
> directly at the input (between input and ground plane)

OK, I'll look at the board and order some ESD101-B1-02s to give it a try.   I think I fixed the issue that blew the input in the first place.  I put a snubber on the DC switch that was introducing transients on the transmission line via the bias tees.

I have a DC motor varying tuning at the antenna and had in the past used a separate pair of wires to drive it.  In a new installation with a longer run, I decided to use bias tees to conduct the DC over the feedline.  That's worked well except for the switch transients blowing the nanoVNA input.  Investigating, I could see them with my o-scope so put together an R/C snubber at the switch to knock them way down.  It needs more analysis and testing, but I think it's solved.

I am wondering if these parts might be better.
PS04LTVA1 or this one 0603ESDA-MLP
Both have Ultra-low capacitance of 0.05 pF, which is less than the ESD part of 0.2 max @ 1mHz.
They are also bigger packages, which may or may not be an advantage. At least I might be able to see them.

Also, there is an "H" version of the switch MXD8641H that has a sligthly higher insertion loss of 0.5dB vs 0.4dB of the MXD8641
But it has a much higher compression point of 36dBm vs 27dBm of the MXD8641.

On Wed, May 1, 2024 at 10:00 AM, NC4BR wrote:

>
> I am wondering if these parts might be better.
> PS04LTVA1 or this one 0603ESDA-MLP...
> "H" version of the switch MXD8641H ...

Thanks for those suggestions.  I'll be receiving the previously discussed parts ( MXD8641 and ESD101-B1-02 ) in a day or so will likely go with those at first.  I understand the higher compression point but am uncertain of how it would manifest in the performance of the V2Plus4.  It does look like the TVS devices you suggest would be easier to solder.  The ESD101-B1-02 just has pads under it rather than the caps over the ends like the ones you suggest.

I examined the board and see there is a 10uF DC blocking cap connected right at the center of the SMA.  There's no good spot to put the TVA before that where it would bridge to the ground plane so am planning to put it after. Correct me if I'm wrong, but I think that may be better than before the cap.  It does seem it would be more feasible to put it before that cap using one the TVS packages you suggest extending one end or the other to bridge the gap.

Hi Lou,

One advantage of placing the ESD/TVS protector on the external (antenna)
side is that the DC blocking capacitor will be protected from high
voltages that tend to build up on some antennas.
I'm guessing the 10uF capacitor has a rating of only 10V or so, and
won't last long when a HF dipole charged up to several kV is connected.

I've been thinking it would be easier to make or modify a commercial SMA
inline lightning arrestor by adding a low voltage TVS diode (since the
commercial gas discharge tubes only start operating way above the
voltage at which the VNA is damaged).

73,
Mark

On 2/05/2024 10:47 pm, Lou W7HV via groups.io wrote:

> On Wed, May 1, 2024 at 10:00 AM, NC4BR wrote:
>
> I am wondering if these parts might be better.
> PS04LTVA1 or this one 0603ESDA-MLP...
> "H" version of the switch MXD8641H ...
>
> Thanks for those suggestions.  I'll be receiving the previously
> discussed parts (MXD8641 and ESD101-B1-02) in a day or so will likely
> go with those at first.  I understand the higher compression point but
> am uncertain of how it would manifest in the performance of the
> V2Plus4.  It does look like the TVS devices you suggest would be
> easier to solder.  The ESD101-B1-02 just has pads under it rather than
> the caps over the ends like the ones you suggest.
>
> I examined the board and see there is a 10uF DC blocking cap connected
> right at the center of the SMA.  There's no good spot to put the TVA
> before that where it would bridge to the ground plane so am planning
> to put it after. Correct me if I'm wrong, but I think that may be
> better than before the cap.  It does seem it would be more feasible to
> put it before that cap using one the TVS packages you suggest
> extending one end or the other to bridge the gap.
>

On Tue, May 7, 2024 at 09:59 AM, Mark Harrison wrote:

>
> I've been thinking it would be easier to make or modify a commercial SMA
> inline lightning arrestor by adding a low voltage TVS diode

There is the Mini-Circuit SMA limiter VLM-33W-2W-S+ $68 at Mouser, Digikey…  though IDK if its limit is low enough for the nanoVNA.

Someone, and it has been too long ago for me to remember, posted about putting a TSV right next to the ant connector. That was for port 1. He put the port 2 one after the cap, but why couldn't port 2 be placed the same? Also, not sure why one looks like a piece of charcoal.