Instructions

Page 44
7.5 Triggered Operation
Triggered operation is only available when the upgrade option U01 is fitted (see section 6).
Triggering is used either to start or stop the sweep, or to initiate logging of sweeps or screen
images. The trigger can be generated manually (by a key press), externally (from the trigger
input) or internally from the sweep in combination with a limit line or limit pattern.
For a description of Triggered Sweep see section 4.4.3.3. For a description of Triggered
Logging see section 7.8.
7.5.1 External Trigger Input
The external trigger input is provided via the 3.5mm jack socket at the top of the instrument.
This can be converted to a standard BNC socket using the adaptor provided. The selection
between positive or negative transition triggering is made from the Sweep Trigger or Logging
Trigger functions. It has a TTL threshold and a high input impedance. Maximum input
voltage is limited to +/-20V. Voltages above this level could damage the instrument.
7.5.2 Trigger Output
A trigger output pulse can be generated using the same socket as trigger input (see above).
The signal is generated by the Limits comparator function (see section 7.7.3) and is a positive
going TTL level pulse of approximately 10ms duration from a 1kΩ source impedance.
The trigger output is not available if either sweep trigger or log trigger is set to external
triggering.
7.6 Level Offset and Compensation Tables
These functions are only available when the upgrade option U01 is fitted - see section 6. They
enable the amplitude scaling to be offset to match external attenuation or gain, or to add
frequency dependent amplitude compensation tables to match transducers or antennae. A
description of the menu keys used to control the function is given in section 4.5.4.
7.6.1 Dynamic Range and Maximum Signal
Adding offset or compensation can create confusion as to the maximum and minimum
signal levels that can be viewed.
This could result in the instrument being in amplitude overload even when the displayed
amplitude value is apparently within the instrument range. Where an offset is set to a large
negative value (to compensate for an external gain element) there is a danger that the absolute
maximum signal level could be exceeded resulting in damage to the instrument - see section
2.1.2.
Offset levels and compensation tables should therefore be used with care !
7.6.2 Creating and using Compensation Tables
Compensation tables are normalised files of amplitude versus frequency that are used to
compensate for frequency related non-linearity in antennae or transducers.
The files contain lists of up to 49 frequency/amplitude points. When a file is used by the
instrument, linear interpolation is employed between the points.
Every point on the trace is then changed by the amount calculated from the interpolated
compensation table. Note that this could result in parts of the trace being outside of the
graticule area.
Compensation Tables must be created outside of the instrument using PSA-Manager software -
see section 6.1.8.