On Tue, 18 Aug 2020 at 00:01, <switchabl@...> wrote:
The SDR-Kits calkits try to fill this gap, but beyond 1.5GHz the
performance doesn't seem to be too great (at least for the female one).
This is maybe not surprising, as they are aimed primarily at the 1.5 GHz
VNWA. I suspect that the issue is mainly with the open and could be solved
if the fringing capacitance were included in the model. If anyone has
measured the SDR-Kits parts with a properly calibrated analyzer up to at
least 3GHz, I would be very interested in the touchstone files.
There¡¯s too much variation from one to the other. You really need the
Touchstone files of the parts you have, which pushes up production costs
significantly.
However, I expect it will be much harder to make a flush open with low
capacitance.
And it is unnecessary to do so.
And I suspect this is the reason why you usually don't find a flush short
in a calkit.
Indeed so, which is why I laugh when I see all these papers and videos
explaining why the delay on the short needs to be so close to zero.
If the difference in delay between the short and open is too large, the
phase will eventually cross-over and the calibration equation becomes
singular.
I think you mean if the difference in phase is too *small*. Yes, indeed
they would, but in practice the kit would become unusable before the
different in phase became zero. I believe about 20 phase degrees difference
is the minimum needed. Below that the calibration would be unstable. Noise
in the instrument would become more significant, as it tried to measure two
devices very similar to each other.
Dave
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Dr. David Kirkby,
Kirkby Microwave Ltd,
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