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Using NanoVNA Saver to capture continuous sweep data #nanovna-saver


mrest 2021/09/23 06:30

Hello,

I am using NanoVNA Saver to record some experimental sensors and am in hoping to get some longer time domain data ideally at a single frequency. I have been using NanoVNA Saver to sweep at a very narrow 1 MHz band but am limited to the 101 points per sweep which makes looking at sensor response to lower (physical) stimuli frequencies very difficult. Is there a way to record the continuous sweep over a set sampling time?

ward harriman 2021/09/23 08:30

I don’t know how to do it with nanoVNA saver but you can probably do it with SimSmith. It would require writing a modernly complicated script. If you’re interested, drop me a note directly.

ward dot harriman at gmail dot com

ward

Jim Lux 2021/09/23 09:27

On 9/23/21 8:30 AM, ward harriman wrote:
> I don’t know how to do it with nanoVNA saver but you can probably do
> it with SimSmith.  It would require writing a modernly complicated
> script.  If you’re interested, drop me a note directly.
>
> ward dot harriman at gmail dot com
>
> ward
>
You can also use the nanovna.py command line utility (which provides a
wrapper around the console commands).  The challenge is that you won't
be able to get a long series of samples at a regular rate, unless the
rate is on the order of 100s of milliseconds/sample.   The firmware
isn't really set up for the equivalent of a spectrum analyzer "zero
span" function.

What you might be able to do is set the number of frequency points to a
small number (I can't remember if it's hard coded to 101), then
repeatedly do sweeps.

You might also be able to use one of the diagnostic functions to read
the nanovna from the console, but then, your timing is going to be
limited by the program that sends the serial commands.  The nanovna is
probably pretty consistent in latency between when command arrives and
when data comes back.  I would think, off hand, that getting samples
every second is certainly doable.

What is probably not doable is getting, say, 100 Hz measurements (if you
were going to do something like measuring heartbeats or microdoppler
effects)

The *hardware* in the nanovna can certainly do this, but to get what
you're looking for might require rolling your own firmware (or
convincing someone else to do it).  Fundamentally, the nanovna samples
at a 1kHz rate (it acquires 1 millisecond of samples, then processes
them), so getting a ~1kHz data stream out is conceivable.  Getting a 100
Hz data stream is definitely doable - allowing for time to grab the
samples, process them, then format for sending them out the virtual
serial port.





Joe Smith 2021/09/23 15:48

On Thu, Sep 23, 2021 at 10:11 PM, <mrest@umd.edu> wrote:

>
> Hello,
>
> I am using NanoVNA Saver to record some experimental sensors and am in
> hoping to get some longer time domain data ideally at a single frequency.
> I have been using NanoVNA Saver to sweep at a very narrow 1 MHz band but
> am limited to the 101 points per sweep which makes looking at sensor
> response to lower (physical) stimuli frequencies very difficult. Is there
> a way to record the continuous sweep over a set sampling time?

Start reading here and let me know if you have any questions.  My signature that thread had the links if you decide to go this route.

https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg3623826/#msg3623826

Jim Lux 2021/09/23 20:19

On 9/23/21 3:48 PM, Joe Smith via groups.io wrote:
> On Thu, Sep 23, 2021 at 10:11 PM, <mrest@umd.edu> wrote:
>
> Hello,
>
> I am using NanoVNA Saver to record some experimental sensors and
> am in hoping to get some longer time domain data ideally at a
> single frequency. I have been using NanoVNA Saver to sweep at a
> very narrow 1 MHz band but am limited to the 101 points per sweep
> which makes looking at sensor response to lower (physical) stimuli
> frequencies very difficult. Is there a way to record the
> continuous sweep over a set sampling time?
>
> Start reading here and let me know if you have any questions.  My
> signature that thread had the links if you decide to go this route.
>
> https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg3623826/#msg3623826
>
> _._,_._,_


That doesn't seem to describe the achievable sample rate at a given
frequency. Typically, for this kind of application, what you want is to
get the I/Q reflection (or transmission if you use separate Tx and Rx
antennas) at a rate above, say, 30 Hz.

In practice, unless you're really close to the subject, you'll see
fluorescent lights (which are a reflector modulated at 120Hz in the US,
100Hz in 50Hz land) modulating the return. the signal reflects off the
wall or floor and then bounces off the lights and bounces back. So a
sample rate of a few hundred Hz is nice.

There's a fair number of people who have done heartbeat detection with a
VNA, in various papers that have been published.

Then, there's an actual device used to detect heartbeats of victims in
rubble (FINDER, which I was heavily involved in developing).
https://www.techbriefs.com/component/content/article/ntb/tech-briefs/physical-sciences/19384

There are also some commercial products for applications like heartbeat
detection for prisoners in a cell or infants in cribs.

Joe Smith 2021/09/24 05:21

OP would need to read the thread to determine if it would work for them.   Their need to collect continuous data at a single frequency was covered in that thread.

If you have an interest in the project I linked in the forum, you should write them.  It's nothing I am involved with.

How is your experiments going when using the two VNAs and T's to replace the transfer relay?   It's been about a month now.  Any luck?

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