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| Kirkby calibration kit alternatives? |
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| Gandalf_Sr:
G0HZU I know you're an expert on VNAs and you may remember that I bought an 8753E a while back, I also got one of the Kirkby Cal Kits. The truth is that, I never really got to understanding the calibration process properly - I'm a trained RF engineer but have forgotten a lot of things. I'd like to request that you mentor me and others here to bridge the gaps in our knowledge; if you're willing; perhaps in a new thread or we could do it here? |
| G0HZU:
If choosing an alternative, a lot depends on what the kit will be used for. Option 1. If you are just going to do fairly casual 1 port VNA measurements up to 3GHz and will be typically looking at antennas or basic matching networks then you might as well make your own from modified SMA end launchers and use 2 x 100R tight tolerance (or select on test) SMD chip resistors to make the 50R load. It wouldn't be that difficult to work out a reasonable USER cal file based on guesstimates of the delays in the short and open. It would cost less than $18 even with new parts? A fairly sloppy version would work to 1GHz but something tight and tidy would be OK to 3GHz for casual measurements. Option 2. If you want to do the same but go up to 6GHz then it gets tougher and the DIY cal kit will not perform well here unless you can generate decent correction coefficients for it. This would mean you would need access to a decent VNA and cal kit to help you set up the USER cal file for the DIY kit. A step up from this would be to buy one of the little SMA kits for maybe $100 and try and tweak up the USER cal data to improve it. Even then it is going to be inferior to a proper 3.5mm cal kit from Agilent etc. Option 3. If you want to do fairly accurate 2 port modelling of DUTs then it gets a bit more serious because you might want to determine the K factor (stability) for an amplifier design for example. Or maybe measure passive SMD parts to create user models of them whilst capturing package resonances. A carefully designed and tweaked DIY SMA kit with an optimised USER cal file could just about do this up to 2 or 3GHz but if you wanted to do this to 6GHz then I think the best option is a healthy/used 85033 cal kit from HP/Agilent/Keysight. As long as it is not damaged it should work well. You would ideally need to be using expensive RF test cables up at 6GHz as well. i.e. cables with minimal phase distortion when flexed. It starts getting expensive very quickly and the cables gradually degrade (in terms of phase and amplitude stability) with regular use. Somewhere in the middle of all this is the Kirkby cal kit. You can consider it too good for option 1 and good enough for option 2. I'm not sure about option 3 if there is a 6GHz requirement. I would want a proper 3.5mm cal kit for this. |
| G0HZU:
--- Quote from: Gandalf_Sr on February 22, 2018, 12:06:09 am ---G0HZU I know you're an expert on VNAs and you may remember that I bought an 8753E a while back, I also got one of the Kirkby Cal Kits. The truth is that, I never really got to understanding the calibration process properly - I'm a trained RF engineer but have forgotten a lot of things. I'd like to request that you mentor me and others here to bridge the gaps in our knowledge; if you're willing; perhaps in a new thread or we could do it here? --- End quote --- This would be best done with a youtube video but, sadly, my presentation skills and video making skills are dire so I'm not really the best person for this. You have a fabulous analyser there that is highly capable and there are loads of powerful things you can do with a VNA like that, provided you have a decent cal kit and it is set up properly. I've not used the Kirkby cal kit but I think it's safe to assume its accuracy up to 3GHz will be very good. Good enough for quite serious work. It's the performance of the kit in the 4-7GHz range I'd be unsure about. It might be really good here too but I'd expect it to need some kind of correction polynomial for the type of SHORT it uses. |
| Gandalf_Sr:
OK, thanks for the advice. I'm travelling right now but I will try to re-calibrate my VNA and then ask the questions along the lines of - Am I doing it right? |
| Mechatrommer:
Anyway, tuning or modelling a diy or stray unknown kit will require a very well calibrated vna in the first place right? Not many people can do that. One of them is kirkby, other than g0hzu... if g0hzu can produce a kit with custom calibration, with proof of vna standard used and cert of calibration at cheap that will be a good option. Vna users, used or cheap version will only want a reliable kit to start with to do their job, not dicking around with sim program and no access to devices capable of modelling a kit with some level of unarguable certainties. |
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