LOCAL OPERATION
3-34
Transmitter frequency
The digits adjacent to the Tx Freq legend on the Tx TEST display refer to the frequency to which
the Service Monitor receiver circuits are tuned.
If the frequency of the transmitter is known, this figure can be entered manually. This is done by
firstly pressing the [Tx Freq] key in the Tx TEST mode menu and then entering the figure using
the data input keys. Complete the entry by use of the appropriate terminator key.
The receiver circuits of the monitor will then be tuned to that frequency and any signal within the
IF pass band will be examined. The frequency difference between the set frequency and the true
frequency will be displayed as ‘offset’.
Hint. When testing a transmitter using sequential tones, it may be necessary to pre-tune the Service
Monitor receiver circuits in this way in order to successfully decode the initial tones.
If the transmitter frequency is unknown, or it is to be measured, key up the transmitter and use the
key sequence [Tx Freq], [Autotune].
The receiver circuits of the monitor will then carry out a sweep to locate the signal and tune to it.
The frequency of the signal is displayed against the
Tx FREQ legend.
*DUPLEX*
The same frequency measurement procedures are applicable when in the Dx TEST mode.
RF distortion, and
Spurious outputs
Distortion of the transmission RF output may be deliberate (modulation is a form of deliberate
distortion), it may be due to a fault or because of design limitations. Whatever the reason the
distortion produces harmonics or other spurious outputs.
These can be located using the SPEC ANA mode of operation.
By viewing the output signals from the transmitter on a voltage vs frequency plot, any
transmissions outside the transmitter's specified bandwidth can be identified.
The use of the SPEC ANA mode is explained fully under that heading.
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