Operating instructions

LOCAL OPERATION
3-23
Modulation meter, demodulation options setup
Set up the demodulation options to be compatible with the transmission from the unit under test.
Press the [Mod Meter] key. The soft keys change to the demod soft keys shown in fold out
diagram (2-3).
Modulation Type
The Service Monitor can demodulate AM and FM signals. The demodulated signal is made
available at the ‘DEMOD OUT’ connector on the rear of the Service Monitor. SSB signals can be
demodulated if the SSB option is fitted.
The [AM/FM] key, or [AM/FM/SSB] key, is used to select the appropriate modulation type by
sequential key presses. The
MOD LEVEL indication within the main display becomes suffixed by
% for AM; and by MHz or kHz for FM. When SSB has been selected, no modulation level is
shown, either digitally or as a bar chart.
Selecting the modulation type for Tx TEST does not change the current modulation type set on the
Service Monitor RF generator.
SSB Input sensitivity
No RF carrier signal is produced by SSB transmitters. Therefore the automatic gain control
circuits of the Service Monitor cannot respond to these signals.
When ‘SSB’ demodulation has been selected, the RF sensitivity of the Service Monitor can be
controlled manually. Three sensitivity settings are given as soft key choices; high, medium and
low. The approximate sensitivities of these are shown in the following table:-
[High Sens]
−90 dBm to −30 dBm at ‘N type’.
−110 dBm to −50 dBm at ‘Antenna’
[Med Sens]
−30 dBm to +20 dBm at ‘N Type’
−50 dBm to 0 dBm at ‘Antenna’
[Low Sens]
+20 dBm to +50 dBm at ‘N Type’
0 dBm to +30 dBm at ‘Antenna’
Hot surfaces
Take care when touching the RF Input Type N connector after the application of
high levels of continuous power. If 50 W is applied for a prolonged period, the
temperature of the connector can become excessive.
IF bandwidth
The IF bandwidth of the Service Monitor receiver circuits can be selected from the following
options:-
300 Hz 3.0 kHz 30 kHz 300 kHz
Press the [IF Filter] key. The right hand soft keys change, to allow selection of IF bandwidth
filters as shown above.
The selected filter is shown on the display. Press the [Return] key after selecting the required
filter.
WARNING