Array Solutions AIM4170 Manual page 8

Antenna Analyzer AIM4170
Then it will display a message box, shown below:
Replace the short circuit with an open connector (included with the AIM4170) and then
click Continue.
The program will run for a few seconds to take several readings of the open circuit.
For the best accuracy, especially at VHF frequencies, use an open connector of the
same type that is used for the short circuit. This allows the program to compensate for
the stray capacitance of the connector itself. For example, 3 pF of stray capacitance due
to a BNC connector represents a reactance of about 1K ohm at 50MHz which will appear
to be in parallel with the load. This will seriously affect readings at higher frequencies if
it is not properly compensated. Therefore, the three calibration devices (open, short,
resistor) should be carefully constructed so they have similar stray capacitance and
inductance which will be cancelled out by the calibration procedure.
NOTE: If you are using the UHF/BNC adapter (or another adapter) leave it on the
output connector of the AIM4170 when calibrating the open circuit. In this way, the
capacitance of the adapter itself will be included in the calibration process.
For example, If you want to use a BNC-to-binding post adapter, calibrate the short circuit
with a jumper wire across the binding posts. Then remove the wire and calibrate the
open circuit condition with the adapter still attached. This procedure cancels the stray
capacitance of the adapter and you can get accurate readings of discrete components
attached to the binding posts.
The calibration procedure can also cancel the effect of a piece of coax that is used as a
jumper to connect the AIM4170 to the load. In this case, the open, short and standard
resistor are connected to the far end of the jumper. Good results have been obtained with
as much as two feet (60 cm) of jumper coax.
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