Operating instructions

LOCAL OPERATION
3-80
Check the modulation polarity of the transceiver. For positive modulation the polarity should be
set to
Normal and for negative modulation, set to Inverted.
The [Polarity] key toggles between these two options.
To enter or change the DCS code for the transceiver to be tested, first press the [Code] key to
highlight the legend
DCS Code:. Key in the code using the data entry keys. The Service Monitor
will accept any octal sequence in the range 0 to 777.
Complete the entry by pressing the [Enter] key. Leading zeros will be suppressed.
Return to the Rx TEST mode and check that the RF generator is active, then return to the TONES,
DCS mode. The DCS coded signal will be produced when the legend
Tone On is displayed
against
Tone Generate Mode:. See Tone ON/OFF control below.
Tone ON/OFF control
When the RF DCS ENCODER screen or the AF DCS ENCODER screen is displayed, the tone is
turned on or off by the orange [ON/OFF] function key.
If the DCS tone is ON and the Tx TEST, Rx TEST, Dx TEST or AF TEST mode selected, the
CTCSS tone will continue to be generated.
If the tones out routing has been set to give RF tones, this is provided by modulation generator 2.
The legend
---DCS--- will be displayed against MOD2 FREQ on the RECEIVER TEST or DUPLEX
screens. If
MOD2 is selected, the DCS tones can be controlled by repeated presses of the orange
[ON/OFF] function key. If
MOD2 FREQ is selected, the DCS tone is still controlled by the
[ON/OFF] key, but if a frequency is entered using the data keys or if the variable control is
adjusted, the DCS tone will cease. It can then be re-started only when the
RF DCS ENCODER
screen or the
AF DCS ENCODER screen is displayed.
If the tones out routing has been set to give AF tones, this is provided by audio generator 2. The
legend
--DCS-- will be displayed against AF2 FREQ on the TRANSMITTER TEST, DUPLEX or
AF TEST screens. If AF2 is selected, the DCS tones can be controlled by repeated presses of the
orange [ON/OFF] function key. If
AF2 FREQ is selected, the DCS tone is still controlled by the
[ON/OFF] key, but if a frequency is entered using the data keys or if the variable control is
adjusted, the DCS tone will cease. It can then be re-started only when the
RF DCS ENCODER
screen or the
AF DCS ENCODER screen is displayed.
DCS transmitter encoder testing
The decoders within transceivers equipped with DCS signaling are usually programmed to
generate their code for inclusion on the reverse channel.
The DCS RF decoder function of this Service Monitor is able to demodulate the DCS signal and
display the digital data.
The DCS signal is fed into a comparator register and occurrences of bit patterns corresponding to
the three ‘fixed bits’ 0 0 1, of the coded signal are flagged.
23 bit samples of the coded signal are placed in registers with the occurrences of the 0 0 1
sequence occupying the 12, 11 and 10 bit positions. The value of the data in bit positions 1 to 9 is
decoded. This corresponds to the DCS code number.
The binary representations of all the decoded sequences are displayed, along with the DCS code.
The oct values are compared with the system permitted codes in a look-up table and the true code
indicated.
The user can select the decoder bit rate to match that of the system, within the range 100 bits/s to
200 bits/s. The modulation level of the data signal is shown on the display.