On Wed, 11 Sep 2019 at 12:49, Kurt Poulsen <kurt@...> wrote:
Hi Reginald
Interesting approach but have you considered that the calibration kits
used then should be from the same supplier else you will have a spread due
to these are having different frequency characteristics and thus add an
uncertainty not justifying the nanoVNA hardware investigation you are
looking for. Just the short used can be with welded center pin and other
with turned disk/center pin, which will introduce a couple of picosecond
variation. Likewise for the open end cap there are many versions I have at
least 4 different models where the one form Amphenol RF has a disk that
close to the center conductor of the female adaptor on the nanoVNA that it
lead to high delays and even often create a short.
Kurt and I don¡¯t always agree on calibration issues???, but in this case
I agree with Kurt.
As I wrote yesterday. I had seen a paper where corrections were derived
when calibrating 3.5 mm connectors with 2.92 mm calibration kits and visa
versa. However corrections were not derived with SMA connectors due to the
variability among them.
Other types have different mechanical structures, actually the best open is
nothing used for frequencies up to 1GHz.
I would be surprised if that¡¯s not the case *well* beyond 1 GHz.
I plotted the data the other day up to 900 MHz, showing added the open
supplied with my NanoVNA just increased the phase from the ideal 0
degrees, as it¡¯s just adding unwanted capacitance.
The load will definitely have frequency dependencies where both the
resistance and inductive / capacitive component influence the frequency
characteristic. There will as well be deviation from sample to sample and
from brand to brand.
That¡¯s why I select every load for calibration kits my company sells.
There¡¯s too much variation among them
These comment not to kill your project but just to raise some concern
Kind regards
Kurt
I am only about 70% sure of Reg¡¯s aim. But if it what I think it is, then
I believe the variation among the SMA bits will make it a bit pointless
trying to collect the data I believes he wants.
Unless good quality N connectors are used, the same issues will arise. In
particular the shape of the male pin N is poorly defined.
Dave
Dave.
--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...
Telephone 01621-680100./ +44 1621 680100
Registered in England & Wales.
Company number 08914892.
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