Operating instructions

LOCAL OPERATION
3-82
Rx test DTMF tones function
In the Rx TEST mode, with [Tones Out] set to RF, the encoder output is fed to the RF generator
and the tones used to modulate the RF signal. The DTMF decoder within the receiver under test
can then be tested.
When setting up the Service Monitor to test the DTMF decoder of a receiver, commence as for
normal Rx tests. When all settings are correct, disable the modulation generators by using the key
sequence [Mod Gen], [Gen 1/Gen 2], [OFF/ON], as appropriate, then the RF generator by using
the [RF GEN], [LEVEL], [ON/OFF] key sequence.
Press the [Tones] key to display the screen shown in fold out diagram (3-5). The [DTMF] key
will then give access to the RF DTMF ENCODER screen.
Formatting a tone sequence
To create the required tone sequence, first press the [Enter Sequ] key to display the cursor in the
tone sequence panel. If the tone sequence panel is not empty use the [DELETE] key to clear the
sequence.
Enter the required sequence by using any of the 16 available characters of the DTMF keypad.
Pressing the equivalent data key on the front panel will cause the character to be entered in the
sequence panel. The cursor then moves to the next position and a second character can be entered.
Any number of Null Tones can be included in a tone sequence. A Null Tone is a silent period, and
has a duration of one tone period. It is indicated in the tone sequence panel by a dash (—) To
enter a Null Tone in a tone sequence, press the [Null Tone] key once.
A maximum of 40 characters can be included in a sequence, any further entries will over-write the
existing sequence.
Editing a tone sequence
An existing tone sequence can be edited as required. Using the rotary control, move the cursor
over the character to be changed. To delete the unwanted character and insert a new character in
its place, press the data key corresponding to the new character. To delete an unwanted character
and close up the sequence, press the [DELETE] key.
Tones modulation level
The modulation level produced by each tone of the tone pair can be set independently.
Pressing the [Lo Tone Level] key will highlight the legend
Lo Tone Level:. The modulation level
can then be set using the data entry keys.
The modulation level produced by the tones is set using the [Lo Tone Level] or [Hi tone Level]
key, followed by use of the data input keys. The modulation level limits are 25 Hz to 75 kHz FM
or 1% to 99% AM. Attempted entries outside of the values will be ignored. The default level is
1.5 kHz.
The modulation level produced by each tone of the tone pair can be set independently. Levels of
the two tones can be locked using the [Lock Levels] key. This key toggles between the locked and
unlocked condition. When going from unlocked to locked, the latest level set will be taken by
both tones.
The tone duration and the pause duration, (time between each tone) can each be set independently,
from 20 ms to 1.0 s. The default values are 150 ms duration and 50 ms pause.
A tones frequency shift facility is provided for testing decoder circuits. To shift the frequency of
the transmitted tones press the [Freq Shift] key to highlight the
Frequency Shift: legend on the
display and enter the percentage value of the shift required using the data entry keys. Frequency
increases or decreases are possible. Entering a negative value will cause the transmitted
frequencies to be decreased from the stated frequency. The maximum frequency shift is 10%.