TECHNICAL MANUAL FOR COMPACT VHF DSC RM2042

3 SERVICE RM2042CHECK OF TX AF DISTORTIONThe TX AF distortion is controlled by measuring the distortion of the TX AF signal at pin 4 in the 9 poleSUB-D connector P2-1 at the interface module.NOTE! To perform this test, it is necessary to change the operation mode of the RM2042 from user toservice mode. This change of operation mode is only allowed for trained technicians and the informationof how to do it is therefore only included in the DSC-VHF INSTALLATION GUIDE.1. Connect a LF-distortion meter to the output of the used TX AF amplifier.Unbalanced TX AF amplifier: use pin 4 (TX AF+) and pin 2 (GND) in P2-1.Balanced TX AF amplifier: use pin 4 (TX AF+) and pin 8 (TX AF-) in P2-1.2. Change the operation mode of the RM2042 from user to service mode.3. Start the transmission of a mark signal by pressing ‘FUNC’ and selecting ‘Test’ and ‘mark’ in thedisplay.4. Control that the distortion is less than 5%.5. Start the transmission of a space signal.6. Control that the distortion is less than 5%.7. Change the operation mode of the RM2042 back to user mode.3.6 ADJUSTMENT PROCEDUREThis section contains the adjustment procedures for all adjustable components in the RM2042.3.6.1 ADJUSTMENT OF INTERFACE (MODULE 1)ADJUSTMENT OF UNBALANCED TX AF AMPLIFIERWhen the RM2042 is operating as an automatic system together with one of our VHF tranceiver, the TXAF output is delivered as an unbalanced signal adjusted in level to give a modulation index of 2, measuredat the transmitter output. During the adjustment, the RM2042 must be connected to the same VHFtranceiver as it is going to be installed with. This demand is motivated by the fact, that the microphoneinput sensitivity may vary from one tranceiver to an other.The unbalanced signal is amplified by the operational amplifier U3.3 and the output level is adjusted bymeans of the trimpot R22-1.NOTE! To perform this test, it is necessary to change the operation mode of the RM2042 and the VHFtranceiver from user to service mode. This change of operation mode is only allowed for trainedtechnicians and the information of how to do it is therefore only included in the DSC-VHF INSTALLATIONGUIDE.1. Connect the RM2042 to the VHF tranceiver by means of the 9 pole SUB-D connector P2-1 at theinterface module.2. Reduce the output RF-power from the VHF tranceiver to 1 Watt.3. Connect a modulation meter through an attenuator to the antenne terminal at the VHF tranceiver.NOTE ! To protect the modulation meter from damages caused by the large outputvoltage, it is necessary to use an attenuator of about 30dB.4. Change the operation mode of the RT2047 or the RT2048 from user to service mode. Select a DSCVHF channel different from channel 70 and change the operation mode back to user mode.5. Change the operation mode of the RM2042 from user to service mode.6. Turn the switch S1-1 at the interface (module 1) into the position: ‘1’.PAGE 3-69403