On 2/6/23 11:36 AM, Brian Beezley wrote:
N6LF has been trying to calibrate his NanoVNA-H4 through a wideband balun for common-mode current suppression when measuring an open wire line ground probe. He has had perplexing results. As a test he tried paralleling two 50-ohm loads, calibrating the VNA with that load, and then measuring it. He did not disconnect/reconnect the load and he measured it immediately after calibrating. He got the results depicted in the plots.
Resistance is off 1 part in 5000 and reactance has an upward creep at LF of more than that. Spikes occur. Are these results reasonable?
1 in 5000 is actually pretty good. That's 0.02% - I doubt the load is known that accurately over that bandwidth.
Similarly, the reactance of the load is probably not zero. 0.1 ohms at 50 kHz is about 0.3 uH. That's the inductance of about a foot of wire. And with the falling reactance with rising frequency, maybe there's a parasitic L and C. (or an offset in the calibration)
