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Document number: S46-901-01 Rev. F / March 2011
Section 2: Connections
S46/S46T/S46L Microwave Switch System Instruction Manual
Oils and salts from the skin can contaminate connector insulators, reducing their resistance. Also,
contaminants present in the air can be deposited on the insulator surface. To avoid these
problems, never touch the connector insulating material. In addition, use the relay only in clean,
dry environments to avoid contamination.
Voltage standing wave ratio
The voltage standing wave ratio (VSWR) is a measurement of mismatch in a cable, waveguide, or
antenna system. The measurement is shown as ratio to 1 (for example, a VSWR of 1.2 is actually
the ratio of 1.2:1). Refer to the specifications located on the Keithley Instruments website
(
) for S46/S46T/S46L VSWR information.
Path isolation
The path isolation is the equivalent impedance between any two test paths in a measurement
system. Ideally, the path isolation should be infinite, but the actual resistance and distributed
capacitance of cables and connectors results in less than infinite path isolation values for these
devices.
Path isolation resistance forms a signal path that is in parallel with the equivalent resistance of the
device-under-test (DUT). For low-to-medium device resistance values, path isolation resistance is
seldom a consideration; however, it can seriously degrade measurement accuracy when testing
high-impedance devices. The voltage measured across such a device, for example, can be
substantially attenuated by the voltage divider action of the device source resistance and path
isolation resistance. Also, leakage currents can be generated through these resistances by voltage
sources in the system. Refer to the specifications located on the Keithley Instruments website
(
) for S46/S46T/S46L isolation information.
Insertion loss
Insertion loss indicates signal lost while passing through the switch. This loss occurs in the various
signal path components through the switch connectors, computer board traces, and relay. Refer to
the specifications located on the Keithley Instruments website (
) for S46/
S46T/S46L insertion loss information.
RFI/EMI
RFI (radio frequency interference) and EMI (electromagnetic interference) are general terms used
to describe electromagnetic interference over a wide range of frequencies across the spectrum.
Such interference can be particularly troublesome at low signal levels, but it can also affect
measurements at high levels if the problem is of sufficient severity.
EMI can be caused by steady-state sources such as radio or television broadcast signals, or some
types of electronic equipment (microprocessors, high-speed digital circuits, and so on.), or it can
result from impulse sources, as in the case of arcing in high-voltage environments. In either
situation, the effect on the desired signal can be considerable if enough of the unwanted signal is
present.
EMI can be minimized in several ways. The most obvious method is to keep the equipment and
signal leads as far away from the RFI source as possible. Shielding the switching switch, signal
leads, sources, and measuring instruments will often reduce RFI to an acceptable level. In
extreme cases, a specially constructed screen room may be required to sufficiently attenuate the
troublesome signal.
