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I am completely new to the concept of VNA's, and am just beginning to grasp what a powerful tool this is. After making some S21 measurements on a broadcast FM trap filter, it began to dawn on me that an S21 measurement might also be an excellent way to test amplifier gain. Obviously I would need to assess whether the amplifier being tested could accept the nanoVNA power level listed in the specs. I have some low noise signal preamps with 20-30dB gain, and can't wait to give it a try...but before I fry my nanoVNA I need some technical advice...

What would be the maximum dBm that the nanoVNA could tolerate going into either of its ports?
For measuring amplifier gain (S21), which port should go to the amplifier input, and which to the output?
Would I need to insert an attenuator before the preamp input so that the output is not out of range that the nanoVNA can measure?
Some of the preamps I have use bias-T to power them...would I have to insert a DC blocker inline with the nanoVNA protect it or the bias-T supply?

Sounds like the problem I had until I learnt the correct calibration procedure.
Try this.


Turn on NanoVNA.
Select desired freq range or default of 50Khz - 900MHz
From the menu press CAL
Press RESET
Then press CALIBRATE
Press OPEN with nothing connected Ch0
Menu now moves to where it says SHORT (a light shade of green)
Connect the SHORT on CH0 and press SHORT
Menu moves to LOAD and turns a light shade of green
Connect your 50R load to Ch0 and press LOAD
Menu moves to ISOLN with a light shade of green.
Keep the LOAD connected on CH0 and press ISOLN
Menu moves to THRU in a light shade of green.
Connect a short lead (provided in the kit from Ch0 to Ch1)
Press THRU
Menu moves to DONE in a light shade of green.
Press DONE
Then press SAVE 0

Done.

Allow a few seconds each time for the unit to do a scan before moving on the next step each time.

73 de Andy

To all,

I did some work on making the application quicker and more robust and corrected some errors
Updated executable; /g/nanovna-users/files/NanoVNA%20PC%20Software/TAPR%20VNA/VNAR4.2.zip

Hi George,
this time I tested a 200 MHz band pass filter. Again, not much difference between the two analyzers.
Now I am convinced that the NanoVNA is worth the money!

Best regards
Norbert

From: Curt M.

Hi guys, mine Nanvna seemed like it was working but I think I messed some setting. If I have nothing connected to the device I see a yellow waveform on CH0 and it reads 10db/ -83.75db and the line under it in blue reads CH0 Smith 1.0FS. 49.9 ohm 1.1mf. If I conned and sma rubber duck antenna to the upper sma connector nothing changed. It acts like sampling is paused or something. What did I mess up?

Is there a way to reset it back to the beginning?

Curt M.
===============================

I see the same, Curt, whether I calibrate from the PC or from the device
itself. It does indicate lower than -10 dB if I test an antenna,
showing -23 dB on the device and -20 dB on the PC trace.

Neither Bruce's nor W5DXP's suggestions made a difference.

Cheers,
David
--
SatSignal Software - Quality software for you
Web:
Email: david-taylor@...
Twitter: @gm8arv

"Pause" command is in the standard firmware.
Upper scanning speed seems to be limited by the setup time of the SI5351 (somewhere between 3 and 10ms) and the 2ms (The source is contradicting, comment says 5ms but 96 at 48khz is 2ms) data that needs to be acquired for each point. Moving to 1ms data will increase the noise

Yes, I can still make changes with the touch screen. Cycling the power didn't seem to do anything different.

While I was typing the above I took a break and started changing some settings. It looks like it's working fine. Now if I only knew what's I did to mess its up and fix it for the next time???

Curt M.

Erik,
The routines that refresh the LCD take up a certain amount of CPU processing.
Even though the scanning is paused, the LCD is still being refreshed via the SPI lines - no?
Does your firmware version turn off all display refresh ie:display goes blank? (I haven't had a chance to install/play with it yet).

Can we remove the display routines altogether and, let's say, increase the scanning speed/etc.
Would you be able to benchmark your version with the display on while scanning and then completely disabled and scanning?

In other words, what can be gained on the device by modifying the F/W to produce a headless unit? Anything?

Regards,
Larry

I ordered mine from ST-EC before I knew about the Hugen version. However, it appears that I received the Hugen version from ST-EC for $48.

For now, I am going to leave a short SMA cable permanently connected to avoid wear and tear on the NanoVNA SMA connector.

Larry,

After a "pause" command all scanning is suspended and only the UI and communication tasks run interrupt driven.
Using the "scan" command I implemented no updating of the ui is done while measuring.
So CPU load is already dramatically reduced.
For a headless device there is no need to do TDR in the NanoVNA so there is no clear need to free up code space.

Or am I missing something?

Did you try turning power off and then back on?

There has been some mention of running the NanoVNA in headless mode - ie:through the USB interface using console commands.

How much processing power would be recovered by disabling and/or removing the display and associated (ie:touch) routines through the Console?

There could be 2 versions of firmware:
1 - Disable all display routines via console command - A power-on reset restores the display
2 - A dedicated headless device with additional flash memory freed-up for other options (TDR?)

A PC, Android tablet, RaspberryPi or other computing device could talk to the hardware through the USB interface and run Python or other applications.

Of course, the Pi could also use the SPI lines but that would be a much bigger task on the Pi side in terms of re-inventing/porting all the low level signal processing routines.

Comments?

Are you still able to make changes to the settings via the touch screen or connected PC?

No clue, test?

On 12/09/2019 12:19, erik@... wrote:

Its 32 bit and you will need dotNet and VC++ 2010 runtime

All dotNet versions??

Its 32 bit and you will need dotNet and VC++ 2010 runtime

/g/nanovna-users/files/NanoVNA%20PC%20Software/TAPR%20VNA/VNAR4.2.zip

Hello Erik

Just for fun I am trying to install your app using Wine on Linux Mint 19.2 64 bit.

What M$ libraries do I need e.g. VC++ runtime, dot Net etc?

Is your executable 32-bit or 64-bit?

73
Nick

Yes, both dutch, I'm waiting for AT to get my ham licence.
Will implement a fix for the mentioned error. Its probably a .dotnet error. Is you windows language set to Dutch.
Can you take the manual and mark where you see differences with the manual?
Attached a word version of the manual

qrp.ddc,
The plot I attached was for a scan I had on hand called "rg316-rg6u-rg58-50R.s1p", sorry for the confusion. The plots for the two files in your original message are attached. They don't seem to show the clearly defined impedance steps you are looking for. Salil Tembe downloaded your files and may be able to give an explanation of the step data shown.