BW Broadcast technical manual
Page 27
Installation and setup
5. We should check that any offsets internal to the limiter are nulled out to keep distortion to a minimum. Connect
a multimeter set to millivolts to testpoint TP1 which is located next to the right clipper jumper. You
will also need an earth point for the meter. The bolt on REG2 is a good earth. The case of the transmitter is not a
good earth due to the allo-chrome finish on the case. Adjust the blue multiturn pot VR3 in the center of the limiter
section for the minimum voltage reading on the meter. Aim for below 10 millivolts. Repeat for the left channel with
VR4 and by taking the reading from test point TP2.
6. Connect an audio source to both channels and apply a 400Hz tone with a level of +6 dbu Make sure the gain
controls are set to maximum (Fully clockwise). These are multiturn so make sure you hear / feel the pots click
indicating end of travel.
7. Adjust the multiplex gain control on the back panel for a peak deviation of 72 kHz. This allows a 3 kHz guard-
band for slight overshoots that may occur in limiter and filters inside the system.
8. Set the limiter to ON with jumper J8. Decide on Clarity or loud mode for the limiter and set Jumpers Jx and Jx
accordingly.
All that is left to do is to set the input gain controls to your desired settings. For most applications where you
require a loud competitive sound we recommend setting the gain controls at maximum, however if you are supply-
ing a very high level feed you may have to turn the gain controls down to stop internal clipping occurring prior to
the limiter. (Please see note on pre-emphasis at the end of the section). You may also wish the limiter to start to
limit for a given level of input. To set the limiters input controls up for a given input level consult step 9. Otherwise
leave the input gain controls at maximum and skip to step 11.
9. Apply your audio feed to the left channel input socket on the rear panel at the desired level you want limiting to
commence. This will need to be a minimum of 0dbu. The limiters inputs will need at least a 0dbu input to achieve
limiting even with the rear panel gain controls set at maximum. Read the pre-emphasis note at the end of the sec-
tion for more info on input level restrictions.
Set the LCD display to limiter gain reduction and with audio applied to the left channel reduce the left channel
input gain control until the display flickers from 0dB to 2dB gain reduction.This is the onset of limiting.
10. Remove the left channel audio and repeat the procedure for the right channel. This procedure also ensures
that both inputs to the internal limiter are driven equally.
11. Set the pre-emphasis jumpers J2 and J3 to the correct setting for your region, 75µs for the Americas and
Japan and 50µs for the rest of the world. If your audio feed has gone through an external processor prior to this
transmitter then check to see if that unit has pre-emphasis capability and if it is switched on. If it has pre-empha-
sis and it is enabled then you should remove the pre-emphasis jumpers J2 and J3 to ensure that only one set of
pre-emphasis has been applied throughout the broadcast chain.
12. Connect as before. Turn the power off to the transmitter, connect your external antenna , reconnect your
power and your on the air!
13. Monitor your total peak deviation with your real world audio material and check with the deviation display that
your peak deviation does not exceed 75 kHz. If you have set up the transmitter as per the instructions in this sec-
tion then you should be within 1 kHz or so of this figure. If your deviation does exceed 75 kHz then adjust the
back panel multiplex control to keep your maximum deviation at 75 kHz.
2.56 Mono from one channel input.
You can provide one audio feed to the transmitter via the left balanced input. This has the advantage of supplying
two exact audio signals to the stereo encoder section that will in turn cancel the stereo subcarrier leaving only a
pure mono signal with content falling to zero above 15 kHz.
Advanced setup procedure.
1. Follow the advanced setup procedure for the ‘mono from two independent channels’ mode completely as if
you would be using that mode. Set all the jumpers and levels correctly as if you would be using that mode. Both
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