Bandwidth / Selective Level Meter; Afc - Automatic Frequency Control; Averaging / Peak Hold - H Heuer Instruments UMDT51A User Manual


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
WIDE:
PSOPH:
25 Hz:
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
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

Press [f3] to select Num of Avgs.

Turn the knob clockwise to increase, or anti-clockwise to reduce, the Num of
Avgs.

Press the
The current setting for Averaging / Peak Hold is displayed in the CONFIG bar
along the bottom of the LCD.
LT51 User Manual
key and then [f3] to display the BW options:
Wideband (from 0 Hz) measurement over frequency span
ITU O.41 Psophometric filter (from 0 Hz) over frequency span
DMM mode only
Make a Selective Meter measurement at the current Centre
Frequency using the selected BW.
key and then toggle [f4] to set AFC ON or OFF
key and then the [f2] "Meas Settings" soft-key.
key (or any key) to clear the dialog box.
Configuring the Tester
32