By the way... can anybody explain how the "reflection bridge" of the KC901V exactly works?
I guess it is the structure that looks like a wilkinson power divider?
its a power splitter as described by TheSignalPath. there must be detailed explanation, concept and math behind it. i will read them up when i want to make my own diy VNA
or if i figure out my VNA is broken and need a tear down. fwiw i guess this type of topology that makes KC901V gives false reading esp impedance value at very low end of frequency 5KHz - 1MHz or so.
fwiw, among other things, attached is attenuator plot provided from Kirkby to me. the result i got on my VNA is much noisier, so i know something went wrong. i'm ordering stuffs to further verify my VNA condition if its fits for measurement etc later. i hope they will not get lost during CNY...
Is that attenuator (reference) plot taken with the 8720D VNA and your cal kit? Or is it a 'best' reference taken of the attenuator with the 8720 and a Keysight/Agilent cal kit?
he claimed he tested all the cal kit sold to me by his own hand. incl the attenuator. so the plot you see should be unique only to my attenuator. i expect other kirkby cal kit owner should have different plot. it took long time (about a week or more) for the calibration to be made, he claimed he do this process in some quantities, to quicken his process. going to lab with my cal kit alone to do the process will take him even longer time, i take and understand this as his economical point of view. furthermore he was not well when i made the purchase i almost cancel the order because it took so long for him that i thought he gave less interest in my order. but i'm glad to support him.
If a calibration kit is made using SMA F-F bullets and end caps there are a few things that will limit its performance. There will be some (extremely tiny) added inductance at the end of the SHORT and also the SMA bullet won't have a perfect 50R Zo. The SMA bullet is about 42ps in terms of delay and this is longer than a regular 85033 cal kit and so this can make any phase variation (due to imperfect 50R Zo) appear slightly worse. The 85033 cal kit uses precision 3.5mm connectors and an air dielectric and it is much better suited for use up at 7GHz.
It doesn't take much to get 4 degrees of phase error over 6GHz in a DIY cal kit. If you get several degrees of phase error and it isn't corrected for by the cal kit corrections then you can expect to see that reference plot degrade a lot by 5GHz and it will get quite noisy by 7GHz. Also, an inline test of a 3dB attenuator isn't a very critical test.
i'm not sure how to reply to this, just as how i'm going to reply to Kirkby in my last test, i'm not knowledgable much that i need to gain some info, do some test (or even need to have access to much expensive gears) to be able to comprehend some of the meaning. i only can hope or rely on some expert to do the testing and give some promise that it should work.
btw attached (1st file) is my translation of the parameters extracted from kirkby's data relevant to my kit and VNA. for open standard, he provided varying offset delays (that i translated from offset delay ps metric in his file into mm). its varying in sub ps range or max deviation (not std deviation, maybe variance) of 0.162 mm throughout the BW. so i just prefer the mean value of 17.357 mm @ 3.5GHz (57-58 ps) to punch in the VNA if i want to do quick testing. fringing capacitance effects should already be lumped in the figures during calculation or modelling). as for short he only provided a single offset delay so i suspect the variance due to inductance effect should be negligible? i never heard of fringing inductance effect for short standard
he should provide the complete data if this is a concern. anyway this only based on trust to the expertise because i'm not at his location during the modelling. if he lied, then i lied
the 2nd attachment is the zipped s1p for my SOL kit, i dont know how to read this and not sure if its relevant to this discussion, i need time to gain on this. 3rd pdf file is my latest test report to him to seek advice. you can see S11 and S22 plot of the terminated attenuator (after calibration with his SOL kit) are quite spot on except at the area of notches which he claimed of high uncertainty even if measured with his 20GHz VNA since attenuator is terminated hence reflecting very little signal for processing. his arguments are quite rational though... and i can accept a $2K VNA will be of no match to the $17K VNA. the concern in the report is S21 you can see the noises i was talking about. he stated the attenuator should not jump up and down 5dB variance in very short BW range. i'm yet be able to reply on this before i can do more testing..
However, I see this process as polishing a turd once you get up to 7GHz. Much better to have a decent 85033 cal kit here.
that Agilent cal kit if well within spec and in full complete data, should be about 2-3X the cost of my VNA. i can see used price is $2K already without any data. i would not give my money betting on that. ps: i'm not sure why Kirkby called his cal kit as 85033E similar to agilent naming. maybe its tracable to the agilent cal kit he owned? and his cal kit is modelled/compared after that? i'm not sure.