Products > Test Equipment
Kirkby calibration kit alternatives?
<< < (4/44) > >>
G0HZU:
FWIW here's a phase comparison plot that may be of interest. This is a relative phase measurement of my homebrew OPEN.

The two measurements were take many years apart and one was with an old HP8753ES with 85033 cal kit at work and the other is with my modern 13.5GHz Ecal module on a fairly modern ENA VNA. This was taken today.

There is a difference and this could be wear and tear and it could be the torque. I used different torque tools.
But the result looks sensible to me. The vertical blip in the data is a 0/360 degree wraparound in the simulator so ignore this.

Next to this is an old plot of my simulation model of the 85033 OPEN that is based on the data in the cal kit as below. I used the delay and the C0, C1, C2 and C3 data in the model and ran it on the simulator. It is compared to an 8753ES doing a self measurement of its OPEN.

60  ! OPEN:  $ HP 85033 Open
70  !    Z0  50.0 $ Ohms
80  !    DELAY  29.243E-12 $ Sec
90  !    LOSS  2.2E+9 $ Ohms/Sec
100 !    C0  49.433E-15 $ Farads
110 !    C1 -310.131E-27 $ Farads/Hz
120 !    C2  23.168E-36 $ Farads/Hz^2
130 !    C3 -0.16E-45 $ Farads/Hz^3

When I was messing with my HP8714B many years ago I calibrated a company HP8753ES with an 85033 cal kit and then used it to remeasure its own OPEN standard. I then exported the data in an S1p file. If I compare the S1p file to the mathematical model for the C0, C1, C2 and C3 polynomial and the delay and compare relative phase I get the plot on the right below. It looks like a flat line.

The VNA is measuring it's own cal kit 'OPEN' so it will display a response of a very tiny length of transmission line that has an open with some fringing capacitance at the end. It does agree with the model. Obviously, the VNA is measuring its own reference here so the result looks good but the point is the simulator model I created does seem to agree very closely.
G0HZU:

--- Quote from: orin on February 21, 2018, 01:07:42 am ---
A fair proportion of that 4 degrees will be the uncertainties in measuring the actual phase of the standards.  According to the datasheet, the 8720D's uncertainty is close to 2 degrees in the 2-8GHz range for a 1.0 reflection coefficient.

--- End quote ---

My suspicion is that due to the fact that the kit uses regular SMA F-F bullets and screw on caps the SHORT will have stray inductance between the interface between the end of the SMA bullet and the metal face/pin in the end cap. There won't be a perfect interface here so there could be a tiny air gap that introduces inductance. This on its own would introduce phase error and it may be that this could be as bad as a few degrees by 6GHz. I don't see any correction polynomial for this inductance on the website and this is probably because not many VNAs support this form of correction. Most only correct for the fringe capacitance in the open.

So the limitations of the kit could be influenced by this inductance for one thing. A regular Keysight 85033 SHORT will perform very well here because it uses a 3.5mm connector with an air dielectric. So there is no dielectric 'gap' at the metal plate at the end of the short as you would get with an SMA connector.
hendorog:

--- Quote from: G0HZU on February 20, 2018, 10:50:07 pm ---
You posted up a link to that (fringe) cal coefficient tool using GNU Octave but it looks like it is still being developed.


--- End quote ---

Yes it's fairly experimental, but I think it should do the job.

I haven't tried it in anger, but I did get it working at least - a while ago. I seem to remember I had to modify it to use a different S-param library than the one they recommend.

One of these days I'll have another crack at it - I have a new contact who has a cal kit who can do the reference measurement for me.
G0HZU:
For my homebrew SMA cal kit here at home I used an RF simulator (that permits equations/scripts) to model the delay and the fringe capacitance and this allowed me to tweak the delay and C0, C1, C2 and C3 using a manual/iterative approach to flatten the phase error on my OPEN. It takes a couple of minutes using the UP/DWN keys on the keyboard to tweak C0, C1 etc to get it flat.

The plot below shows my OPEN being compared with the model after I had optimised the coefficients in the simulator. The OPEN was measured on my ENA analyser after an Ecal and the data compare against the model. It agrees very well :)

technogeeky:
I just wanted to point out these male SMA references available for about $20 in the USA.

They manufacturer link goes back to mRS miniVNA Tiny and Pro's website.  After more and more searching, it seems like these guys are the manufacturer (or at least they have made measurements of the 50 ohm SMA load part).

The measurements they offer are here. I doubt this is sufficient for converting into a format you could input into a VNA characterization, but I just wanted to point out that they exist.

I am going to get a pair just as an additional set of open/short/load calibrations since my current best set are homemade, and because they have them in stock in their Atlanta, GA location which is down the street from me.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod