On Wed, 3 Jul 2019 at 04:04, <hugen@...> wrote:
Yes, calibration data can only be modified with electrical delay.
What exactly do you mean by that? Are you saying that the firmware has the
ability to allow one to adjust the delay of the calibration standards? If
so that¡¯s good news. Just being able to enter a delay for the standards
will be a vast improvement over having no control whatsoever.
But someone else wrote ideal standards were assumed.
For better accuracy, I customized the shortest and most accurate
calibrations kits possible.
There¡¯s no need to make the shortest calibration standards possible, *IF*
one can enter the delay of the standards.
*The internet is full of people claiming incorrectly the need to have the
shortest possible delays on calibration standards. * If you look at the
delays on professional calibration kits, you will find they are *longer* on
modern high-end kits than they were on obsolete kits!
The obsolete HP/Agilent 85032B type-N calibration kit had delays of
Female Short = 0.000 ps
Female Open = 0.093 ps
Those are the shortest possible delays one can make on female N.
Now if you compare those figures to the current $20,690 high-end 18 GHz
85054B kit, you will find the delays are much longer in the modern kit.
Female short = 27.990 ps
Female open = 22.905 ps
For the lower cost ($2410) 9 GHz 85033F 9 GHz kit, the delays on the female
parts are:
Female Short = 45.995 ps
Female Open = 41.170 ps
*So very approximately, for female N calibration standards:*
Obsolete 6 GHz kit - delays around 0 ps
Current $2410 9 GHz kit - delays around 43 ps
Current $20,690 18 GHz kit - delays around 24 ps
Clearly on female N parts, it¡¯s possible to make delays close to 0, but
Keysight don¡¯t use them.
The same general principle is true for the male N standards, but in that
case it is impossible to make a zero delay. If you check the links I gave
above, you will find the following.
*Very approximately, for male N calibration standards:*
Obsolete 6 GHz kit - delays around 17 ps
Current 9 GHz kit - delays around 43 ps
Current 18 GHz kit - delays around 60 ps
For obsolete HP 3.5 mm kits, the delays were from memory were around 17 ps,
but any of the modern kits (85033E, 85052D or 85052B) all have delays of
about 30 ps.
Naturally, the accuracy of professional
calibration parts cannot be achieved.
That statement is a bit ambiguous.
If you are saying that a high end VNA is best used with a professional
calibration kit, I would agree with you.
However, if the NanoVNA firmware always assumes idealised parts with a
delay of zero, then things would change *dramatically*. One could easily
make more suitable opens and shorts than would would have if one spent
$2410 on an 85032F. Spending even more, buying the $20,690 85054B would
give you even less suitable open and short standards.
The loads from the $20,690 kit would always be the best loads, but of
course it would be crazy to use loads that probably cost $1500 each on a
VNA costing less than $100.
Unfortunately, some clone makers do not understand the role of the
calibration kit, providing a poor quality load to act as a calibration kit,
which can result in worse measurement results.
Yes, clone makers often don¡¯t appreciate or care what crap they turn out.
But a lot of self-proclaimed experts, writing web pages about how to make
calibration kits don¡¯t understand what they are doing.
My own company, Kirkby Microwave, does care and we have enough knowledge to
understand most of the intricacies. I cringe at some of the stuff I see
written on the internet about VNA calibration kits.
hugen
gen111.taobao.com
Dr. David Kirkby
Kirkby Microwave Ltd.
<>
--
Dr. David Kirkby,
