Re: Trying to understand the T-Check outcome of the nanoVNA
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Hi Erik
Three problems. First of all you have not subtracted the delay of the Thru adaptor (2 x 62ps) when calibration s11/s22 as you remove the thru adaptor after s11 calibration and thus the calibration plane are 124ps out in the blue air. Second when measuring s21/s22 you must subtract the delay of the thru adaptor (1x62ps) from the calibration as then you have same phase at the two male SMA adaptor for the two test cables. That is why the T check is only some + - 20% and as seen for my image for 500MHz span as I throw away all points above 500MHz. Third the range above 900MHz is "stupid" to use as useless When above is done the T-Adaptor is sitting between two calibration planes where s11/s22 and s21/s12 are correct placed at the two calibration planes being identical to the measurement plane Good luck with the next steps Kind regards Kurt -----Oprindelig meddelelse----- Fra: [email protected] <[email protected]> P? vegne af erik@... Sendt: 25. september 2019 16:54 Til: [email protected] Emne: [nanovna-users] Trying to understand the T-Check outcome of the nanoVNA Using a not too good BNC Tee I performed a T-Check Attached the measurement (.s2p) and the excel file (.xlsx) in which the T-Check is calculated. Next to the T-Check calculation the excel also calculates the abs(Zin-Zout)/Z0 (the percentage absolute distance of the two impedances as another estimate of error) The frequency is denoted in MHz Do ignore anything above say 500MHz The T-Check suggests the error quickly increases to substantial levels but the abs(Zin-Zout)/Z0 suggests there is a very systematic error in my measurement where the absolute distance of the two rotating impedances grows very linear with frequency. I did calibrate using the Tee without (OSL) and with (T) the outgoing cable connected but maybe that did result into the error. What am I doing wrong? |
Kurt Poulsen
