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KC901V not showing correct resistance at near DC...

By soasystem •  2017-10-02 01:46:39 •  315 clicks
hi new KC901v owner here. sw ver 1.1.8, hw ver MB V1.2, RB V1.0.5... my issue is KC901V not showing correct resistance at near DC. the VNA will always start showing 50 ohm resistance and then gradually heading to the right resistance. for example, if i put 100 ohm termination at the coax end, it will start at 50 ohm [see attached picture]. can the device showing correct resistance at DC or near DC [100-500KHz]? i hope for firmware upgrade for this. waiting your reply thanks.
2 Reply | until2018-10-21 08:23Add a reply
    soasystem  2017-10-03#1 -Reply

    but capacitor reactance should be infinity at DC right? checking the reactance (Z -> X) at DC, KC901V showing zero. i suspect this has to do with poor directivity of directional coupler (or power splitter?) at DC that FW has to predict starting from 50 ohm and as the freq increase, reading converge to the true value. i hope there is a way to start reading R at DC and hence prediction should start from that DC resistance.

    g7psz  2017-10-03#2 -Reply

    I do not have a 901v, (only an elderly 901s) but surely your trace is demonstrating that the input is ac coupled; ie there is a capacitor there (mainly for protection) and the trace is showing the reactance of the capacitor at the low frequency end of the trace.

    If I (or you) could be bothered, the value of the dapacitance could be calculated from the information on the screen.

    Once the scan has passed a few hundred khz, the capacitance has negligable effect and the 50ohm load is then displayed.


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KC901 serial VNA