LOCAL OPERATION
3-80
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 DSC 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.
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