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If the factory set C0 values were made with a better SOLT than provided with the nanoVNA, can these values be stored? Or would recalibration with the supplied SOLT be as accurate as those set by the factory? Would the factory set C0 values need to be different for different versions of the firmware? I realize the C0 values were scanned at a course (wide span) of frequencies. Still at individual frequencies, they may be better than those that can be obtained with the supplied SOLT. Any ideas?

By C0 do you mean channel zero default cal that came with the unit?

Or are you referring to the description of the standards?

It is my understanding that the firmware assumes that the standards are IDEAL.

Alan

I was referring to the C0 contents when the nanoVNA was shipped. I think the standard SOLT units are about as close to ideal as manufacturing constraints and cost constraints make possible, and that the VNAs have to assume these standards are close to ideal. Otherwise the standards would come with estimates of their deficiencies and that these deficiencies could be corrected for while calibrating. Thus the original C0 contents COULD be better than the cheaper SOLTs can calibrate to -- or perhaps not. Perhaps the supplied SOLTs were used, and perhaps used carelessly at the factory. I have no knowledge of this, and was hoping for some discussion -- and help in determining if the original C0 values should be kept, or if it is best to recalibrate using the supplied SOLT right from the start.

On Sun, 11 Aug 2019 at 00:45, Bob Shaw <ve3suy@...> wrote:

If the factory set C0 values were made with a better SOLT than provided
with the nanoVNA, can these values be stored? Or would recalibration with
the supplied SOLT be as accurate as those set by the factory? Would the
factory set C0 values need to be different for different versions of the
firmware? I realize the C0 values were scanned at a course (wide span) of
frequencies. Still at individual frequencies, they may be better than those
that can be obtained with the supplied SOLT. Any ideas?

A proper calibration kit has values for C0, C1, C2,C3 and an offset delay.
My company produces such kits. However, the NanoVNA firmware assumes ideal
standards with no offset lengths, and no fringing capacitance, *so any
better quality calibration kit would produce poorer results.* That
situation will remain unchanged unless the firmware is updated to allow one
to specify an offset length for both the open and short as well as C0, C1,
C2 and C3 for the open.

Actually, at 900 MHz, for a low specification VNA, just having an offset
delay would be tolerable. The fringing capacitance could either ignored, or
the offset delay increased a little to take the capacitance into account.

For female SMA connectors, with male calibration standards, the standards
will be fairly close to ideal. The biggest problem will arise with female N
tests ports and so male N calibration standards

Sace

--

Dr. David Kirkby,

Hello Bob,

I seem to recall reading on one of the eBay vendor's auction pages for a NanoVNA, some wording that claimed the following: "The buyer should not worry that the picture shows a NanoVNA with a range of 50 kHz to 300 MHz. The unit that will be shipped will have a firmware upgrade to allow operation from 50 kHz. to 900 MHz. and it will be calibrated to factory standards using the same included calibration devices." Of course, when I went back and tried to find that listing - I couldn't.

In my opinion, I don't think that any seller would be using "better" standards to calibrate the unit than the standards they were shipping with the unit. None of these manufacturers or sellers are trying to compete with HP/Agilent/Keysight or any of the other VNA manufactures out there. They all just want to build and ship a unit that meets the advertised specifications and do that as inexpensively as possible to maximize their profit. I see nothing in it for the seller.

Certainly the end user can take the supplied C0 data and save it in one the other Memory locations (SAVE1 thru SAVE4) and then load C0 with some other data so that it is always readily available at power-up. This would allow the initial data to be reloaded into C0 at some other time. But I have not seen or read any reason to believe that the factory furnished C0 calibration data is any better than the data that can be recreated using the furnished calibration tools.

I offer all of this IMHO.

Larry, AE5CZ