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| Kirkby calibration kit alternatives? |
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| hendorog:
--- Quote from: in3otd on February 25, 2018, 08:34:37 pm --- --- Quote from: hendorog on February 25, 2018, 07:23:09 pm ---Then I found a bug in the model calculation for the Lx params. Fixed that and tada, now it lines up :) --- End quote --- :-[ uh, oh, you mean the indices of the Lx coefficients were off by 1in the std_model_s_params() function, right? I'll upload a corrected version shortly, thanks! --- End quote --- Haha, welcome! I was considering sending you an email to let you know we were discussing your code here! Yes that was the issue. I just figured you hadn't used L params much due to the 8753 et al not supporting them. |
| in3otd:
--- Quote from: hendorog on February 25, 2018, 07:54:24 pm ---Also, if the cal is done offline in software, then changing coefficients (i.e. recalibrating using a different set of coefficents) is purely software and doesn't require another sweep. So it would be technically possible to do a full sweep and change cal definitions on the fly. The definitions would match the real cal standards very closely. --- End quote --- If you have a VNA where you can access to the calibration coefficients, like the 8753 and, I think, most of the ones not targeted at hobbyists, you can simply use something like scikit-rf to do the calibration using the calkit S parameters directly (no need of building any model of them) and then write the computed calibration coefficients back to the VNA. I don't know if this is what the METAS VNA Tools can actually do or if it allows only a post processing of raw data acquired from the VNA. Then another issue is the calkit repeatability, with cheap stuff you never know how it will behave tomorrow :) |
| hendorog:
--- Quote from: in3otd on February 25, 2018, 08:51:39 pm --- --- Quote from: hendorog on February 25, 2018, 07:54:24 pm ---Also, if the cal is done offline in software, then changing coefficients (i.e. recalibrating using a different set of coefficents) is purely software and doesn't require another sweep. So it would be technically possible to do a full sweep and change cal definitions on the fly. The definitions would match the real cal standards very closely. --- End quote --- If you have a VNA where you can access to the calibration coefficients, like the 8753 and, I think, most of the ones not targeted at hobbyists, you can simply use something like scikit-rf to do the calibration using the calkit S parameters directly (no need of building any model of them) and then write the computed calibration coefficients back to the VNA. I don't know if this is what the METAS VNA Tools can actually do or if it allows only a post processing of raw data acquired from the VNA. Then another issue is the calkit repeatability, with cheap stuff you never know how it will behave tomorrow :) --- End quote --- Yes, very true. In this way we can remove the model entirely. With the cal kit repeatability issue, I think that is where buying high quality open/shorts and characterising them should produce a better result than DIY. Also, the proposal I mentioned a while back, was to not use an open standard at all when the VNA has a female SMA port. As long as it is characterised then is there any point in connecting a standard to it, aside from a slight noise reduction? This is one less connection to make when calibrating. I need an s1p file from a calibrated VNA which has a female SMA port left open. Since we have optimisation software, I will try to create a model for it. |
| G0HZU:
--- Quote ---Also, the proposal I mentioned a while back, was to not use an open standard at all when the VNA has a female SMA port. --- End quote --- I've done that with a known SMA barrel at the end of an SMA cable and I have a very 'short' male SHORT made from a cut down Suhner (good quality) SMA connector. See the image below. It is possible to just use an SMA end cap for the short instead but the end cap will obviously spin as it is being undone so this can cause wear. The short below has a nut that can still spin (so no wear issues) but this means it has some delay in it and the performance isn't great and I don't use this very often and I try to only use it below 1GHz. |
| hendorog:
--- Quote from: G0HZU on February 25, 2018, 10:07:48 pm --- --- Quote ---Also, the proposal I mentioned a while back, was to not use an open standard at all when the VNA has a female SMA port. --- End quote --- I've done that with a known SMA barrel at the end of an SMA cable and I have a very 'short' male SHORT made from a cut down Suhner (good quality) SMA connector. See the image below. It is possible to just use an SMA end cap for the short instead but the end cap will obviously spin as it is being undone so this can cause wear. The short below has a nut that can still spin (so no wear issues) but this means it has some delay in it and the performance isn't great and I don't use this very often and I try to only use it below 1GHz. --- End quote --- For the short I was intending to use these parts. These are the ones used in the SDR kits. I have one of their Male kits so I already have the male short below. Female short: http://sdr-kits.net/documents/32Z114-000L5.pdf Male short: http://rosenberger.de/ok/images/documents/db/32Z111-000L5.pdf The wear issue is a bit tricky. I believe the Male below can spin internally (am not near it right now to verify), but the Female obviously can't and so would need to be held still while the nut is tightened. The specs for both say 500 mating cycles. However I am sure they will change their characteristics over their lifetime - as in3otd alluded to. |
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