R.V.R. Elettronica PTX30 UHT/S3, User Manual

Page: 40 / 122

PTX30 UHT /S3
34 / 36 User Manual Rev. 5.0 - 10/12/2001
•
Disconnect the audio signals on both channels and leave the PILOT TONE
inserted; verify that a deviation of 6.5 to 7.5KHz is present.
This value can be adjusted with P6 on the coder board.
•
Disconnect the audio signal from one channel and verify that the output level of
the audio generator is 0dB.
On the stereo measure decoder, you should read a separation of more than 50dB
at 400Hz. Take the reading on the other channel.
If the separation between the two channels differs more than 3dB, you can balance
it adjusting P4 on the coder board.
10.2 Main card adjustment
• After inserting the main card and the relative connectors proceed as follows
(figure 10.1):
• Select 0 dBm with the INPUT LEVEL selector, coder and pilot tone inserted.
• Connect the R.F. output to a dummy load.
• Connect the R.F. Test -30dB coupler to the RF input of F.A.M..
• Connect to the rear FM-MPX output of F.A.M. a stereo measurement decoder.
• Send a 0 dBm (0.775Vrms 2.2Vpp) 400 Hz tone to L, R inputs.
• Check with F.A.M. set in FM PK+ mode and with the 30Hz-200Khz filter inserted
that the deviation is 75KHz; if necessary adjust R45 on the main card to obtain
this value.
• Disconnect the pilot tone pushing the button and set the F.A.M. for distortion
measurement; adjust R44 for the minimum of distortion.
• Repeat again the procedure described two points ago.
NOTE: for these adjustments, you must use an audio generator with a distortion
lower than 0.001%. Perform these adjustments at the operating frequency.
10.3 Modmeter adjustment
• See figure 10.1, than connect the RF output to a dummy load.
• Connect an audio generator to the L and R inputs with an output of
400Hz at 0 dBm
• Connect the R.F. Test -30dB to the R.F. input of F.A.M..
• Select 0 dBm with the Input Level Selector, insert the coder and the pilot tone.
• Select 100% on the switch.
• Adjust trimpot R30 on the modmeter board so that the first red led lights (the
led coinciding with the 100% mark).