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Does it need new calibration every time when different frequency range is selected?
Or is it enough just one initial full freq. calibration?

On 1/30/23 3:42 AM, PDXer wrote:

Does it need new calibration every time when different frequency range is selected?
Or is it enough just one initial full freq. calibration?

That depends on the level of accuracy you want. If you do a full range cal, and then set a narrower range for the measurement, it interpolates from the full range cal. That may or may not be great (particularly at the points where it changes which harmonics to use, at N*300 MHz points)

If you cal over, say, 0-900, and there's 100 points, that means there's a calibrated point every 9 MHz. Leaving aside the "transition points between harmonics" it's likely that the device's internal errors (what you're calibrating out) smoothly vary in amplitude and phase between points.

OTOH, if you are calibrating with a fixture or coax in the system (e.g. you've got 50 ft of coax, and you're doing the cal at the end of the coax, to measure your antenna at the feedpoint) then you potentially have a problem -That 50 ft of coax has multiple wavelengths (and a different number of wavelengths, depending on frequency) - and 9 MHz between calibration points may have one or more phase wraps. Now, linear interpolation might not work so well.

The other thing where you definitely want to recalibrate for the "range of use" is where you want the best possible measurements. Why interpolate if you can use real data?

For what it's worth, I cal 0-100 MHz (because it's easy) when working with HF stuff.

And, if you're using an application (like NanoVNA-Saver, and others) that does multiple sweeps to get more points in the range, then you can calibrate with fine resolution over a wide range.

Depending on your firmware version, you can save multiple sets of calibration data.

I saved all five sets in my nano, specifically, 3 Mhz to 15 Mhz, 15 Mhz to 30 Mhz, 3 Mhz to 30 Mhz, 143 Mhz to 149 Mhz, and 420 Mhz to 450 Mhz,? I then load the calibration data as needed for the antenna span being checked.

David
AK9F

Jim

I calibrate a coax pig tail that connects to my antenna system (50ft + UnUn
+ Wire + Counterpoise). That way, I eliminate a known good out of my
measurement by “calibrating out” the known good. I have also worked my way
out of diagnosing the antenna system by measuring the window connection,
coax then with unun + antenna + wire. Not sure if this is best practice or
where I learned it. Just seems to make logical sense. How are others doing
it? From posts I have read, it seems people just wing it without any
logical step thru of the antenna system!

On Mon, Jan 30, 2023 at 9:14 AM Jim Lux <jimlux@...> wrote:

On 1/30/23 3:42 AM, PDXer wrote:

Does it need new calibration every time when different frequency range

is selected?

Or is it enough just one initial full freq. calibration?

That depends on the level of accuracy you want. If you do a full range
cal, and then set a narrower range for the measurement, it interpolates
from the full range cal. That may or may not be great (particularly at
the points where it changes which harmonics to use, at N*300 MHz points)

If you cal over, say, 0-900, and there's 100 points, that means there's
a calibrated point every 9 MHz. Leaving aside the "transition points
between harmonics" it's likely that the device's internal errors (what
you're calibrating out) smoothly vary in amplitude and phase between
points.

OTOH, if you are calibrating with a fixture or coax in the system (e.g.
you've got 50 ft of coax, and you're doing the cal at the end of the
coax, to measure your antenna at the feedpoint) then you potentially
have a problem -That 50 ft of coax has multiple wavelengths (and a
different number of wavelengths, depending on frequency) - and 9 MHz
between calibration points may have one or more phase wraps. Now,
linear interpolation might not work so well.

The other thing where you definitely want to recalibrate for the "range
of use" is where you want the best possible measurements. Why
interpolate if you can use real data?

For what it's worth, I cal 0-100 MHz (because it's easy) when working
with HF stuff.

And, if you're using an application (like NanoVNA-Saver, and others)
that does multiple sweeps to get more points in the range, then you can
calibrate with fine resolution over a wide range.






--

73, ko4aqf@...

Great info & advice. Thanks.

On Mon, Jan 30, 2023 at 02:25 PM, David Rounds wrote:

Depending on your firmware version, you can save multiple sets of
calibration data.

I saved all five sets in my nano, specifically, 3 Mhz to 15 Mhz, 15 Mhz
to 30 Mhz, 3 Mhz to 30 Mhz, 143 Mhz to 149 Mhz, and 420 Mhz to 450 Mhz,?
I then load the calibration data as needed for the antenna span being
checked.

David
AK9F

On 1/30/2023 5:42 AM, PDXer wrote:

Does it need new calibration every time when different frequency range is

selected?

Or is it enough just one initial full freq. calibration?

Yeah, I think my set allows 6 or 7 setting savings, and can recall them I remember in the menu.
It seems a great idea. Putting on the tiny Open Short Load bits unto the SMA port and taking them out can be a bit of pain, if it has to be done often. But saving and recalling the calibration settings for most commonly used frequency ranges sounds solving the problem. cheers. 73.

There is one particular use case where no calibration is needed at all, and that is when tuning a magnetic loop or similar antenna, where the only adjustment is resonant frequency. The S11 VSWR/log mag dip will be at the same frequency regardless of calibration status.
73, Don N2VGU

On Mon, Jan 30, 2023 at 03:56 AM, PDXer wrote:

Does it need new calibration every time when different frequency range is selected?

Yes.

On Tue, Jan 31, 2023 at 12:44 AM, Donald S Brant Jr wrote:

There is one particular use case where no calibration is needed at all, and
that is when tuning a magnetic loop or similar antenna, where the only
adjustment is resonant frequency. The S11 VSWR/log mag dip will be at the
same frequency regardless of calibration status.
73, Don N2VGU

Good point as well.