H Heuer Instruments UMDT51A, User Manual

Page: 44 / 104

Configuring the Tester
LT51 User Manual 32

If the current display is in DMM mode, then the selective level at the current
centre frequency is displayed. The Selective BW, is set to ‘
25 Hz
’ by default.

In Spectral mode, the display is adjusted to show the centre frequency in
the centre of the display and the start and stop frequencies on the axis are
calculated for the currently set frequency Span. The BW is set to
‘
CENTRED’
.
NOTE: Making measurements with the centre frequency set, can noticeably
slow the update rate of results and spectral displays.
Bandwidth / Selective Level Meter

Press the key and then [f3] to display the BW options:
WIDE: Wideband (from 0 Hz ) measurement over frequency span
PSOPH: ITU O.41 Psophometric filter (from 0 Hz ) over frequency span
25 Hz: DMM mode only
Make a Selective Meter measurement at the current Centre
Frequency using the selected BW.
1.74 kHz:
3.1 kHz:
The current setting for
BW is displayed below the frequency axis or under the
frequency result in DMM mode.
AFC
– Automatic Frequency Control

Press the key and then toggle [f4] to set AFC ON or OFF
With a centre frequency set, and the BW set to 25Hz, 1.74 kHz or 3.1 kHz, the
LT51 will automatically track small
changes in the received signal’s frequency,
close to the centre frequency. The Centre frequency value will be automatically
set to the incoming frequency, to allow for slow moving drift of this signal.
When AFC is active, the symbol “AFC” will be displayed instead of “Fc” next to
the centre frequency in main numerical display.
Averaging / Peak Hold
Press the key and then [f5] to toggle Averaging between OFF, AVG and
PK HOLD.
To change the number of samples that are averaged:

Press the key and then the [f2] ”Meas Settings” soft-key.

Press [f3] to select Num of Avgs .

Turn the knob clockwise to increase, or anti-clockwise to reduce, the Num of
Avgs .

Press the key (or any key) to clear the dialog box.
The current setting for
Averaging / Peak Hold is displayed in the CONFIG bar
along the bottom of the LCD.