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LOCAL OPERATION

3-81

DTMF

Overview

Dual Tone, Multi-Frequency.

The DTMF tones function will generate and decode sequences, of up to 40 characters

corresponding to the standard DTMF frequencies.

The encoder allows the user to create characters sequences which are routed to the AF GEN

OUTPUT connector or to the RF generator modulators.

The decoder will accept up to 40 tone pairs, either from the modulation meter output or as AF

signals from the AF INPUT connector.

Tx test DTMF tones function

In the Tx TEST mode, with[Tones In] set to RF, DTMF tones generated within the mobile under

test, are recovered from the RF signal and routed to the DTMF decoder.

The RF frequency and modulation type of the transmitter under test is set up from the Tx TEST

mode.

Pressing the [Tones] key will display the screen shown in fold out diagram (2-5). The [DTMF]

key will then give access to the RF DTMF DECODER screen shown in Fig. 3-26, RF DTMF

DECODER screen and menu.

The decoder measures the frequencies and duration of each tone pair, identifies the character, and

calculates any frequency errors. The results of this are listed on the display as shown.

Fig. 3-26 RF DTMF DECODER screen and menu

The bottom of the screen contains two tables. The tone frequencies table on the left lists the eight

frequencies, LO1 to LO4 and HI1 to HI4, used for DTMF signaling. The table on the right shows

the 16 digit/character/symbol keypad with the LO tones and HI tones matrix.

The panel at the top of the display area shows the contents of the DTMF decoder memory. A

maximum of 40 symbols can be stored, any additional symbols will not be accepted.

The central area of the display, which is blank when first accessed, lists the measured frequencies

of ten of the received tones. The underscore in the decoded character panel of the display

indicates which characters are listed. The left hand column shows the measured frequencies of the

‘LO’ tones with the percentage error, the center column the corresponding ‘HI’ tones with error,

while the right hand column shows the duration of each tone.

To display the next 10 decoded results, press the [ F ] key. To display the previous 10 decoded

results, press the [ E ] key.

The display can be printed and the results stored on a memory card.

To clear the contents of the decoder memory press the [Clear Sequ] key. Once cleared, they

cannot be retrieved.

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Aeroflex 2948B Betriebsanleitung Seite 135