User's Manual

5-48
5.20 IN-SERVICE XMTR CARRIER NULL ADJUSTMENT USING SPECTRUM ANALYZER
See the following figures and follow the procedure to adjust carrier null on the UD-35A()
Transmitter, in service. For out-of-service carrier null procedures, refer to CD.
Carrier leakage can be nulled in the MDR-8000 using any one of three
methods. Method 1 (the preferred method) uses a spectrum analyzer to
determine if carrier leakage is present while a modulated signal is
being transmitted (in service) and then nulling any carrier present.
Methods 2 and 3 require that modulation be removed and the carrier is
nulled while the transmitter is out of service. Method 2 uses a DVM to
measure carrier leakage. Method 3 uses a spectrum analyzer.
Using the spectrum analyzer Span controls, reduce the frequency span until the
Resolution Bandwidth (
Res BW ) reaches the value defined as the Res BW for measuring
carrier . At this Res BW , observe the spectrum trace for a carrier signal. If a carrier signal,
rising above the spectrum floor, 3 dB or more is visible, use the procedure to null the
carrier. If no carrier is visible, the carrier is sufficiently nulled.
Ensure that the radio, and specifically the transmitter unit, is
allowed to warm up for at least one hour operating in the
radio before performing carrier null adjustments.
Note
CAUTION
Possibility of
Service
Interruption