Impedance question
The Autec Analyser is a better instrument than the MFJ for
suspended-in-mid-air measurements. It is much smaller and is lighter
in weight and has a smaller capacitance.
The Autec case has a self-capacitance of the order of 3 pF
corresponding to a reactance of 1768 ohms at 30 MHz which can be
ignored when measuring 50 ohms with zero lead length.
The Autec's highest frequency is 35 MHz.
The MFJ's highest frequency is at VHF. With a self-capacitance of 7
pF at VHF substantial errors can occur.
To estimate capacitance, the DC capacitance of a sphere is -
pF = 55.55 * Diameter in metres.
----
Reg.
|