Is the nanoVNA able to measure the characteristic impedance of a short stripline?
For dead-bug builds it is sometimes required to have a 50ohm stripline to connect two adjacent parts of the circuit.
One approach is to use a small coax but according to the stripline calculator that can be found here
using a small isolated wire and some copper foil should also give about 50 ohm.
So I made a test PCB and added a rather high-tech stripline consisting of a thin insulated wire and some copper foil covering the wire and keeping it close to metal layer of the PCB.
One end of the wire is connected to the center pin of a SMA connector and the other end is connected to ground
Then I connected the nanoVNA to the SMA connector using a male-male and tried to use the TDR function of the nanoVNA to measure the characteristic impedance of the stripline.
It is possible to see the effect of adding the copper foil as the maximum impedance nicely reduces from above 150ohm to 67 ohm but the resolution of the TDR is on the edge of being able to see something.
The measurement point selected was the point with the highest impedance when no foil was added.
Replacing the test PCB with a 50ohm load gives 50ohm at the same measurement point and using a 1k5 resistor to ground on another test PCB showed the measurement point to be the highest resistance.
Replacing the test PCB with a short give -4ohm
Is there a better way to measure sripline impedance with the nanoVNA, or is this the maximum possible?
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NanoVNA Wiki:
/g/nanovna-users/wiki/homeNanoVNA Files:
/g/nanovna-users/filesErik, PD0EK
