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Alan,
The schematics are in the Wiki.
There are only resistors in the input pad. You need to measure them to see which is fried. Hopefully, you didn't fry the SA612 input.

If you have 2 soldering irons with fine tips, you can lift each off the board easily but remember the display is on the other side of the PCB - so not too much heat.
It's not that hard - I flipped the resistors on my Nano-H to see if it helped with the noise (msg thread on that in 2019).
If you have a junk box, you might be able to find replace SMT resistors on scrap boards.

So S21 has been damaged when I was checking a LNA, i gapped it for 2 seconds and hooked the attenuator on the wrong side.
It is a H4, I was going to order a new one as needed pass through on most things I use it for.
Anyone know how to fix, is there a diode or anything that blows when input is to high?

On 2/17/22 7:52 AM, William Smith wrote:

Just make sure, as others have pointed out, that you don’t have any other wires (power supply, USB to computer,, etc) connected to the nanoVNA.

I'm not sure a USB cable would make a difference if the feedline is properly "isolated" from the environment. (i.e. the USB cable isn't coiled up with the transmission line).
I can't think of a physical mechanism for that to cause a problem.

One could easily test it with the NanoVNA by itself, and then with the cables hooked up. If there no difference, then knock yourself out using a PC app to control the VNA.

73, Willie N1JBJ

On Feb 17, 2022, at 10:10 AM, Jim Lux <jim@...> wrote:

On 2/17/22 5:52 AM, WB2UAQ wrote:

We're measuring impedance here. No matching transformer is needed. Just a 1:1 high common mode Z balun. From the Z's measured you determine the characteristics of the balanced transmission line OR and that includes its electrical length. Let's not over complicate things here.

Considering that the NanoVNA is smaller than a lot of HF baluns for balanced lines, I don't think you need the balun, either (until you get up to where the NanoVNA is a significant fraction of a wavelength - maybe don't use it for UHF TV twinlead.

Sorry - that should be 3v at each of the points, not between.
Now, with that said, I just had weirdness with my Nano-H - it wouldn't boot.
It turned out the Enter button (I installed buttons on mine) was pushed-in.
Everything was fine when I un-stuck the button.
Check your rocker switch to make sure it's not stuck in as that would put your H4 into DFU mode with no display lit.

I measured it while unplugged from USB, I get 3.4V between VDD and Ground but no voltage between VDD and the capacitor in the picture.

The only thing at this point is to measure the VDD out of the 3v regulator to make sure it's working.
Schematics are in the Wiki.I've attached an early H4 PCB image for you.

Your battery is defective - get a new one or have a look at some of my early posts where I used a cellphone battery.
/g/nanovna-users/attachment/223/0/Battery-PCB-MiscShields.jpg

my nano vna Hugen v4 shows full battery but after about 10 seconds turn
off.... connected to USB port works fine

On Thu, Feb 17, 2022 at 10:35 AM Brady Nelson <tbradynelson@...>
wrote:

Hi All,

My Nano VNA-H will not turn on after charging. It had been sitting for a
while, so I assumed it was the dead battery, but after charging, the
battery is at a good voltage but the screen will not turn on. Doesn't want
to turn on via USB either. Any ideas what could be causing this?

Sorry should have been clearer, it doesn't turn on even with the battery disconnected.

Correct - that is controlled by the charging/inverter chip.
Can you turn your Nano turn on when connected to USB and the battery is disconnected?

Hi Larry,
When I disconnect the battery and plug the USB in the LED blinks as if it is charging.

sorry for double post, didn't realize my other one went though.

Just make sure, as others have pointed out, that you don’t have any other wires (power supply, USB to computer,, etc) connected to the nanoVNA.

73, Willie N1JBJ

On 2/17/22 5:52 AM, WB2UAQ wrote:

We're measuring impedance here. No matching transformer is needed. Just a 1:1 high common mode Z balun. From the Z's measured you determine the characteristics of the balanced transmission line OR and that includes its electrical length. Let's not over complicate things here.

Considering that the NanoVNA is smaller than a lot of HF baluns for balanced lines, I don't think you need the balun, either (until you get up to where the NanoVNA is a significant fraction of a wavelength - maybe don't use it for UHF TV twinlead.

On 2/16/22 11:28 PM, Bob Ecclestone VK2ZRE wrote:

I'm wondering if the correct way to measure the length of window line
with a NanoVNA is fundamentally different than that of measuring coax.

I'm following the method described by Arie
(/g/nanovna-users/message/26832). I have 5.175m of "JSC
1320 300 Ohm Ladder Line 300 Ohm 20 AWG / 7 Strands Bare Copper". That's
a quarter wavelength of 20.7m, or a frequency of 14.5MHz.


First things first, a FULL ELECTRICAL wavelength at 14.5MHz is 300/14.5 ~= 20.7m. A quarter wave ELECTRICAL length is 5.172m.
To find the PHYSICAL length for a quarter wave stub at 14.5MHz, MULTIPLY the ELECTRICAL length by the cable VF.
The Spec Sheet for 1320 TV Ladderline is 0.82. Therefore the PHYSICAL length required is 5.172*0.82 = 4.241m.

If you now want to prove this, you can use the NanoVNA, BUT it is best if you use a broadband matching transformer and measure the 300 Ohm ladderline in balanced mode.
If you try measuring the ladderline directly on the 50 Ohm unbalanced S11 input of the NanaVNA, you will get unreliable results as you have already discovered. Possible reasons are mentioned in other posts in this thread.

It is unclear why you'd get unreliable results for measuring *electrical length* without a balun - given that the NanoVNA is tiny, and isolated from other things. That is, the "unbalanced-ness" of the VNA is irrelevant when looking at a piece of balanced transmission line, unless there's some weird layout that has the transmission line laying next to the VNA.

The 300 ohms (or 100-120 ohms looking at twisted pair) means that one can't directly use the S11 or R+jX values, but the *distance* measurements should be just fine. The impedance of a balanced line with the other end open goes through the same cycle (at the same frequencies) of apparent short (at 1/4 wavelength), to apparent open (at 1/2 wavelength), to apparent short (at 3/4 wavelength), etc.

What wouldn't be necessarily valid is loss measurements (which is a handy feature of a VNA measurement, not only do you wind up with the length of the cable, but you get the loss at various frequencies)

We're measuring impedance here. No matching transformer is needed. Just a 1:1 high common mode Z balun. From the Z's measured you determine the characteristics of the balanced transmission line OR and that includes its electrical length. Let's not over complicate things here.

Hi Brady,
Did you try disconnecting the battery and powering the Nano from a USB source?
Sometimes when the battery gets too low, the CPU can get into a weird state (assuming you have the battery sense diode installed).

(also, please don't double-post - if you need to, please delete the previous post so we can keep forum somewhat clean)
Thanks,
Larry

Hi All,

My Nano VNA-H4 was sitting for a while, and after charging will not turn on. I checked the battery voltage, it is fully charged. The red LED works, not sure what to do next. Any help would be appreciated.

Agree with Kevin. Very good explanation.

John, wa3jrs

Bob, thank you so much for your very detailed answer. It'll take me awhile to get the ferrite and build the test jig, but I'll let the group know of my results. Thank you, again, for so generously answering my question.

-Kevin
KC3KZ

I have the same looking unit with the same firmware. It says it is supposed to go to 3ghz but mine only allows 2.413ghz as top end.
Have you tested yours to 3ghz?