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| Kirkby calibration kit alternatives? |
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| Mechatrommer:
--- Quote from: Noy on November 19, 2020, 12:48:29 pm ---All the expensive calkits are already up to >>10GHz which is not needed for "cheap" VNAs like siglent ones which are only up to 3.2GHz. Why aren't there affordable ones for less than <150€ with measured values? --- End quote --- Kirkby SMA kits thats advertised as 6GHz are specified to 12GHz using 20GHz calibrated HP VNA, dont ask the CAL kit he uses as The Reference. to convincingly rate a kit to 3GHz, you may want to specify to like what? 4-6GHz? using calibrated reputable brand VNA like HP/Agilent/Keysight, that is still expensive investment, dont ever call them to quote for the CAL kit alone we'll come back in shame, to get the idea, check on used (out of spec) market in ebay. if target customers are hobbiests, its sad hobbiest always aim for cheap price (me included), making this unpleasant business to venture. going to companies and universities, they will tend to go beyond 10GHz with todays 5G age. so you could end up with an expensive piece of paperweight on your desk without return profit. among all, most of Kirkby's customers are universities and professors thats impressed by him. we dont go into the know-how knowledge yet for the reliable calibration/verification process. inside the usb drive of CAL kit profiles, Kirkby included bunches of app notes relating to his work (i guess free non copyrighted) materials mostly from HP, i think i've only read one or two of the materials. |
| switchabl:
--- Quote from: Mechatrommer on November 19, 2020, 12:21:05 pm ---as i said it does not matter actually if we dont care about polynomials. but my thought is, if they want to sell a nice cal kit set, why they let us to go to trouble to buy separate shielded Open? maybe it will cost them only extra $1. --- End quote --- Because it makes very little difference and if it does, it will likely make the performance slightly worse. Shielding an open standard does not help against fringing capacitance, it introduces more of it. If you think about it, the dust cap is essentially one plate of a capacitor. The same is true with these cheap male "calkits": don't bother with the open "standard", just leave the connector open. Use dustcaps to protect from dust, not for calibration. I hasten to add that of course a properly designed open standard for higher frequencies should be shielded (and some care goes into doing it in a way that capacitance is reduced), because the open connector eventually becomes an antenna otherwise. But we are talking 5-6GHz+ there. --- Quote from: Mechatrommer on November 19, 2020, 12:21:05 pm --- --- Quote from: switchabl on November 19, 2020, 11:37:09 am ---I don't know why all the cheap NanoVNAs all come with male ones. --- End quote --- because the Nano has female input? or they figured it is better (more configurable) and they dont have to provide M-M thru. male cal kit can always be connected to F-F thru to get female version. i find F-F thru is inevitable and i very seldomly reach for M-M thru version. --- End quote --- Yes, the test port is (usually) female, but then most often there is a M-M test cable to connect to the DUT. And you really should calibrate at the end of the cable, not at the VNA port. "Converting" a cal kit with a F-F adapter will degrade performance significantly. --- Quote from: Noy on November 19, 2020, 12:48:29 pm ---A decent / cheap "Calkit" for < 4-6 Ghz would be nice. All the expensive calkits are already up to >>10GHz which is not needed for "cheap" VNAs like siglent ones which are only up to 3.2GHz. Why aren't there affordable ones for less than <150€ with measured values? --- End quote --- As you can see from the Rosenberger kit, the individual parts are not exactly free even without the characterization (if you want reliable parts from a reputable brand). And that is re-purposing jelly-bean parts like a thru for an open. Having a purpose-built open standard made in the really low volume we are talking about would be prohibitively expensive. And then you need an expensive VNA with a reference cal kit, pay for regular calibration and maintenance and pay for the lab technician who actually does the measurements. |
| Noy:
[/quote] As you can see from the Rosenberger kit, the individual parts are not exactly free even without the characterization (if you want reliable parts from a reputable brand). And that is re-purposing jelly-bean parts like a thru for an open. Having a purpose-built open standard made in the really low volume we are talking about would be prohibitively expensive. And then you need an expensive VNA with a reference cal kit, pay for regular calibration and maintenance and pay for the lab technician who actually does the measurements. [/quote] For sure, i thought something like "calibrated" VNA with a "pogo plug SMA" and a machine putting it on the pogo plug, measure the value write it down into an excelsheet and throw away, put the next onto the pogo plugs.. something like that. "Fully automized" than calkits with SMA for <6GHz would be cheaper... |
| Mechatrommer:
--- Quote from: switchabl on November 19, 2020, 01:13:48 pm ---"Converting" a cal kit with a F-F adapter will degrade performance significantly. --- End quote --- imho no, except with extra effort to screw unscrew for connection and reduce usable life of the connectors. with good continuity/connectivity and good quality 50 ohm Zo thru, connecting to Open and Short will only increase its offset length, the rest of parameters are still the same. connecting to a good Load will still appear 50 ohm to the VNA. but well, this is true given the CAL set is of descent quality, if not, even a SMA cable or the sacrificial adapter connected to your VNA can look funny. this can quite visible beyond 3GHz and much lower with nonsense hunglow grade. ymmv. |
| switchabl:
--- Quote from: Noy on November 19, 2020, 01:24:46 pm ---For sure, i thought something like "calibrated" VNA with a "pogo plug SMA" and a machine putting it on the pogo plug, measure the value write it down into an excelsheet and throw away, put the next onto the pogo plugs.. something like that. "Fully automized" than calkits with SMA for <6GHz would be cheaper... --- End quote --- Ha, unfortunately, that won't work. There are some "snap-on" RF connectors, but they won't mate with SMA. Especially for calibration purposes, there is just no way around properly tightening it to a matching connector (with a torque wrench). Also, even if it were technically feasible, how many of those do you think you could sell? This is a tiny market. |
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