TN910 Rev 5-0-0 May 14
TN910 Codan MT-3 and IFR COM-120 Test Procedures
MT-3 Radio Systems
TECHNICAL NOTES
Page 13 of 16
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Auxiliary (AC-3E) Input Audio Levels:
The auxiliary audio input level is set while measuring the transmitter deviation. Ensure that the IF BW is set at 30
KHz and the MOD METERS LOW PASS FILTER is set at for 20 KHz.
1. Ensure the transmitter is set to KEY TX and the Audio Control Card IS plugged into the subrack.
2. Connect AUDIO/DATA GEN OUT on the IFR COM-120 to the Auxiliary Balanced Audio Input (1 or 2).
3. Highlight AF GEN OUT and select ZOOM. Enter an audio level of 1.10 Vp (0.777 Vrms or 0.0 dBm).
4. Adjust the Auxiliary Balanced Audio level adjustment (R120 for Aux In 1, R123 for Aux In 2) for a transmitter
deviation of ± 60% maximum deviation (±3.0 KHz wide / ±1.5 KHz narrow)
CTCSS Encode:
The CTCSS encode tone can be supplied from a CTCSS decoder (encode is same tone as decode), a separate
CTCSS encoder; or some base stations may be confi gured for the tone remote adapter to supply the CTCSS
encode tone. These procedures are for use when the audio control card supplies the CTCSS encode tone (with a
decoder or encoder).
1. Ensure the transmitter is set to KEY TX and the Audio Control Card IS plugged into the subrack.
2. Ensure that the CTCSS encode switch is turned ON (if applicable).
3. Disconnect the Tx Balanced Audio Input from the AUDIO/DATA GEN OUT connector on the IFR COM-120.
4. In the RECEIVE window, set the IF BW at 15 KHz as shown in Figure 16.
5. Highlight LINE and select CONFIG, then set the MOD METERS LOW PASS FILTER for 300 Hz as shown in
Figure 16.
Figure 16: IFR COM-120 CTCSS Test Confi guration
Adjust the Transmitter CTCSS deviation for ±0.50 KHz wide / ±0.35 KHz narrow (the adjustment pot is located
directly on the CTCSS module in the audio control card). The CTCSS encode tone is the AF Frequency.
This product has been discontinued and is no longer manufactured by Codan Radio Communications
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