T.E.M. A07B500S, Manual

Page: 47 / 131

A07B500S manual
Pag. 47
Inject a 400Hz signal and +6dBm level in the LEFT input, switch into STEREO and adjust RT7 of
the MBA board to read still 75KHz deviation also for MPX channel.
Adjust also RT1 if the subcarrier deviation at 19KHz is not the 10% of the total and adjust again the
previous RT7 trimmer.
Adjust the RT1 trimmer of the MBA board so that the limitation is symmetrical, on the
upper and lower part of the wave form injected with a level higher than 6dB over the nominal.
Adjust the RT6 trimmer of the MBA board to fix the clipper intervention threshold at the
required value over 75KHz.
Adjust the RT1 trimmer of the synthesis board to have the exact frequency deviation with
the input
Inject a 400Hz signal and +6dBm level in the LEFT input, switch into STEREO and adjust RT7 of
the MBA board to read still 75KHz deviation also for MPX channel.
Adjust also RT1 if the subcarrier deviation at 19KHz is not the 10% of the total and adjust
again the previous RT7 trimmer.
Adjust the RT1 trimmer of the MBA board so that the limitation is symmetrical, on the
upper and lower part of the wave form injected with a level higher than 6dB over the nominal.
Adjust the RT6 trimmer of the MBA board to fix the clipper intervention threshold at the
required value over 75KHz.
Adjust the RT1 trimmer of the synthesis board to have the exact frequency deviation with
the input nominal level presence.
Adjust the RT2 and RT3 trimmer of the MBA board for the maximum stereophonic
division.
On the MBP card, it is also possible to regulate the phase difference of the two LEFT and
RIGHT channels, reducing the cross-talk of the stereophonic signal up to values above 50dB.
The average phase difference between the two channels, once regulation is in place, is less
than 0.5
?
from 30Hz to 15KHz.
For adjustment, it is necessary to inject a nominal level signal on the LEFT channel with the
transmitter set in mono; next, connect an oscillator on the LF output monitor and verify that at
1KHz, the measured signal is approx. 2V. The input frequency is then raised, and two output
minimums are found: the first being approx. 19KHz (+- 500Hz), the second approx. 22.5KHz (+-
500Hz).
There are two exact notch frequencies; at this point, inject the input signal into the RIGHT
channel. Bring the frequency of the audio generator to the exact frequency of the second notch
(approx. 22.5KHz) and regulate the RT10 trimmer for minimum output. Bring the frequency to the
exact value of the first notch (approx. 19KHz), and regulate RT9 again for the minimum. Now
prepare a sweep-generator with 30Hz to 15KHz frequency and at nominal level. Set this signal on
the two LEFT+ and RIGHT- positions in parallel so that, theoretically, the transmitter having been
set in MONO, modulation should be cancelled out. This condition can be observed at all times on
the LF output monitor by synchronizing the oscilloscope with the sweep-generator. The null
condition, or more precisely, of minimum signal, can be achieved by regulating first the RT8 (acts
on frequencies above 5KHz) and then RT11 (acts on frequencies less than 15KHz). After these
operations, the two low-pass filters on the two channels will have a minimum phase difference; the
two filters are comprised of resistances with a tolerance of 0.1% and high Q capacitors with
tolerance of 0.25%.