Firstly, thanks Martin 9A2JK for the User Guide. It's excellent!

I purchased my H4 from AliExpress for under £40 (It's slightly above that now):

https://www.aliexpress.com/item/1005005848060542.html

Having read the User Guide, I had a couple of questions:

How is the SD Card used? It's a pain every time I switch it on having to do the same process of hiding all but one of the traces. Can I save settings so the default is just one trace is active? I see no mention of SD Card usage in the manual.

If I'm only measuring HF frequencies do I need to calibrate every time I turn the device on? Do things like temperature impact the device?

Thanks

Peter Jones M0LMG

Hi Peter,

If you go to the menu, select Config then Save Config once you have everything setup as you would like, then you won't have to disable traces etc.

No, you don't have to calibrate every time you power on. But be aware that chacges in the measurement plane (where the device is connected relative to the port) will affect the calibration. So if you have calibrated directly connected to the port, then connect to your coax run to test an antenna, your results will not a true representation of the actual results as the measurement plane would have changed.

Temperature changes should not affect the device as long as those changes are within reason.

The SD card can be used to save and recall calibration settings, save screenshots, save results of a scan, and other things that have not come immediately to mind.

Hope that helps

Paul M0CNL

Paul,
Save Config doesn't save the trace setup. SAVE in the CALIBRATE menu does that (and saves the frequency range, too).
--John Gord

The calibration save also saves the trace setups. And whatever is saved in
slot 0 is used at power-on

On Fri, Sep 20, 2024, 6:28 PM m0cnl via groups.io <m1cxz.m0cnl=
gmail.com@groups.io> wrote:

Hi Peter,

If you go to the menu, select Config then Save Config once you have
everything setup as you would like, then you won't have to disable traces
etc.

No, you don't have to calibrate every time you power on. But be aware that
chacges in the measurement plane (where the device is connected relative to
the port) will affect the calibration. So if you have calibrated directly
connected to the port, then connect to your coax run to test an antenna,
your results will not a true representation of the actual results as the
measurement plane would have changed.

Temperature changes should not affect the device as long as those changes
are within reason.

The SD card can be used to save and recall calibration settings, save
screenshots, save results of a scan, and other things that have not come
immediately to mind.

Hope that helps

Paul M0CNL

Yes Stan and John, you are both correct. I realised my mistake and all my typos as I was re-reading my reply after sending.

Thank you both for pointing out my error though.

Paul M0CNL

As I understand it, you have to calibrate for each START/STOP or CENTER/SPAN that you use. If you SAVE each one on the VNA or SD card you can recall a saved span and you don't have to calibrate for THAT range again. But if you use a new range that isn't saved you must calibrate for it...

Yes, but if your new range is a subset of the original range, you will
still get very good results without recalibration, because the nanovna
firmware interpolates the calibration points. For ixample, I calibrate
1MHz - 30MHz, and then zoom into individual bands and still get very good
results on my H4 with 401 points. I wouldn't do the same with 101 points
because there aren't enough points for good interpolation. And whenever I
need precision impedance measurements, I do recalibrate using my desired
range. It is more important to recalibrate when the measurement plane
changes, e.g. using longer or shorter cables to the test fixture, etc.

On Sat, Sep 21, 2024, 1:31 AM Matthew Rapaport via groups.io <quineatal=
gmail.com@groups.io> wrote:

As I understand it, you have to calibrate for each START/STOP or
CENTER/SPAN that you use. If you SAVE each one on the VNA or SD card you
can recall a saved span and you don't have to calibrate for THAT range
again. But if you use a new range that isn't saved you must calibrate for
it...

Hi Stan... Yes I understand about changing cables and connectors as well, but I hadn't thought about the sweep points... If I have a saved calibration done at the default 101 points but doing a measurement--same frequencies and connectors--at 401 points do I need to recalibrate for that change?

Typically, it does linear interpolation from the saved calibration. So as long as your fixtures don’t have “weird” impedance variations AND they’re <<wavelength in size, the interpolation should work fine.

Two caveats: At the frequencies where harmonics change (300 MHz on original NanoVNA), the calibration “across” the jump is probably not linearly interpolatable.
If the electrical length of the fixture (which might be a 30 meter long coax cable, for instance) is long enough where you get more than ~180 degree phase shift, interpolating the values might hiccup, because of the phase wrap. (It would depend on how the interpolation is implemented.. a >360 degree phase shift would certainly cause problems)

Yes that would work generally well, being a 1:4 interpolation. But do keep in mind the considerations Jim described. I believe the firmware does a cubic spline interpolation, so it give quite good results except at the most abrupt discontinuities (e.g. phase reversal).
A way to think of the points and interpolation is this: If I have a 101 point calibration across, say 30MHz of HF bands, then 'zoom in' to 1MHz on the 14MHz band, I have 1/30th of the calibration points, only about 3 of them, in my new range. The firmware will interpolate across these, but it isn't much to work with, and could lead to inaccuracies if the calibration is not linear in that region. With a 401 point calibration in this same scenario, there are 12 points to use for interpolation, which will give a result with a much higher confidence factor. (If your device supports 401 points, I would always use them - I don't know of a reason not to, unless you need ultra-fast sweep speeds).
And if you extend your sweep range beyond the current calibration, the interpolation doesn't have any points to use, so it will continue its same interpolation slope, with no data to guide it. I do this sometime for quick measurements that are not critical, but it certainly is best to re-calibrate.

Thanks guys... So I'll spend an hour recalibrating all my saved ranges at 401 points. I don't use subsets of saved calibrated ranges, but it can't hurt! 😂

Thanks everyone for the information. Lots to read and experiment with.

I did look in the Wiki, but could not see any mention of maximum SD Card size and how it should be formatted? Could anyone help? Thanks/

On Mon, Sep 23, 2024 at 06:33 AM, Peter Jones wrote:

I did look in the Wiki, but could not see any mention of maximum SD Card size
and how it should be formatted? Could anyone help? Thanks/

Not all SD cards work with the H4 due to the way the firmware is implemented. I use a 32 GB Kingston card and it works fine. You just have to try a few brands to get one that works for you

Roger

Max size is 32M. I bought a pack of 5 inexpensive 16GB Patriot cards from
Amazon, and they work fine.

On Mon, Sep 23, 2024, 10:25 AM Roger Need via groups.io <sailtamarack=
yahoo.ca@groups.io> wrote:

On Mon, Sep 23, 2024 at 06:33 AM, Peter Jones wrote:

I did look in the Wiki, but could not see any mention of maximum SD Card

size

and how it should be formatted? Could anyone help? Thanks/

Not all SD cards work with the H4 due to the way the firmware is
implemented. I use a 32 GB Kingston card and it works fine. You just
have to try a few brands to get one that works for you

Roger

I use a generic 16gb flash card with formatted with FAT32.

Terry

I sure would like a copy of that user guide. Is a link to it posted
anywhere?

On Mon, Sep 23, 2024, 12:01 PM Terry W7AMI via groups.io <terry.w7ami=
gmail.com@groups.io> wrote:

I use a generic 16gb flash card with formatted with FAT32.

Terry

On Tue, Sep 24, 2024 at 12:55 AM, Steven Hays KA9MOT wrote:

I sure would like a copy of that user guide. Is a link to it posted
anywhere?

Please have a look at the files section here.
https://groups.io/g/nanovna-users/files
https://groups.io/g/nanovna-users/files/Absolute%20Beginner%20Guide%20to%20The%20NanoVNA

Sorry but the Max size of SDCard is 32G not 32M.

"Max size is 32M. I bought a pack of 5 inexpensive 16GB Patriot cards from
Amazon, and they work fine."

Clyde KC7BJE

Oops. Thank you for the correction, Clyde. I typed to quickly without
reviewing.

On Tue, Sep 24, 2024 at 11:03 AM Clyde Lambert via groups.io <clyde.lambert=
gmail.com@groups.io> wrote:

Sorry but the Max size of SDCard is 32G not 32M.

"Max size is 32M. I bought a pack of 5 inexpensive 16GB Patriot cards from
Amazon, and they work fine."

Clyde KC7BJE