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Operator Manual for TACT TA-4800 in NSW National Parks & Wildlife Service User Mode G/00123B Issue 1 Page 20
AUDIO LEVEL ADJUSTMENTS
Please Note:
The TA-4800 Tx and Rx audio levels are factory preset to suit most
popular radios. Therefore field adjustment is generally not required, and we
recommend that you try using TACT before attempting the following set up
procedures. It is also recommended that you use parameters *71 and *72 in
the System Configuration menu if tweaking of the Tx and Rx levels is
required.
AUDIO OUTPUT TO RADIO (Tx LEVEL) (SETTING THE MODULATION LEVEL)
This procedure is to adjust the Tx audio level from the telephone line to the radio.
The audio output from TACT to the radio is found on Pin 7 of the
‘RADIO’
connector. It can be connected to the radio’s
mic input or similar point. The TACT keypad is used to adjust the audio level to radio for correct modulation. If using
microphone sensitivity input, a 10:1 resistive voltage divider across the mic input circuit is recommended.
The Tx level setting procedure is as follows:
1.
Press *97# on the TACT keypad. TACT will respond by transmitting an 820 Hz test tone via the base radio to the
mobile for 120 seconds. With an appropriate test set connected to the base radio transmitter output, repeatedly
press * to increase or # to decrease the test tone (you can also press a digit 1
9 to select an absolute level and
then fine tune with the * and # keys) until the test set indicates the correct modulation level. (Refer to the radio
manufacturer’s documentation and appropriate regulations for relevant specifications. For FM sets the signal should
deviate the RF carrier 2.5kHz on systems with 25kHz channel spacing or 1.25kHz on systems with 12.5kHz channel
spacing).
If a suitable test set is not available, use an ac Volt meter to monitor the input to the radio and repeatedly press
* to increase or # to decrease the signal level to match the input specifications of the radio. For example, a
radio may require 100 mV at its input. (You can also adjust the level by ear. Listen to the test tone on a
receiving mobile, and using the procedure described above, adjust the level until it sounds clear and free of
distortion).
2.
Press 0 to save and exit. TACT reads back a two digit value for Option *71 in the system configuration options.
AUDIO INPUT FROM RADIO (Rx LEVEL)
This procedure is to adjust the Rx audio level from the radio to the telephone line.
Audio output from the radio (300
500 mV p-p recommended) is fed into TACT via Pin 8 of the
‘RADIO’
connector. As
a last resort, the radio speaker output may be used as the audio source. The input impedance of the TACT radio receive
audio port is normally 10K Ohms or 600 Ohms nominal with LK15 linked.
To meet ACA specifications, the DTMF audio level from TACT to line should not exceed -6dBm. The radio being used
should be adjusted so that -6dBm to line is not exceeded.
The easiest method to calibrate the Rx level to line without expensive or additional equipment is as follows:
1.
Make sure that the level from radio to TACT is less than 1V RMS.
2.
Connect the telephone line to Line 1 OR apply a dc loop current (from part number LI-4302 active line driver) to line
1. Place a dB or ac Volt meter across the line.
3.
Press *98# on the TACT keypad.
4.
Press and hold 5 on a mobile radio keypad to provide a continuous tone from the radio to the TACT.
5.
Repeatedly press (on the TACT keypad) * to increase or # to decrease the signal (you can also press a digit 1
9
to select an absolute level and then fine tune with the * and # keys) so that the output level is around -6dBm or
0.388 V RMS.
You can also observe the TACT display and adjust the level until the display just changes from 6 to 7.
6.
Press 0 to save and exit. TACT reads back a two digit value for Option *72 in the system configuration options.
