Solidyne 542 APC, Owner'S Manual

Page: 23 / 44

3.8 Calibrate the modulation
The pilot tone is factory set at 9% and the RDS carrier at
4%. Usually it is not necessary to change these values. If
modifications are required, it must be done BEFORE per-
forming the modulation adjustment.
To adjust the modulation index of the transmitter proceed
as follows:
✔
Go to the Stereo Generator setup screen. Turn on
the 542APC CALIBRATOR. The input audio will be
replaced by a sinusoidal tone of 400Hz.
✔ Tune the transmission to the internal tuner of the
542APC and check the processor modulation me-
ter for the 100%. For fine tuning, set the MPX out-
put level from the 542APC’s web page (the default
level is 5 VPP).
✔
The 542’s modulation meter shows the peak level.
If the transmitter has its own modulation meter,
check the modulation in both meters.
✔ Turn OFF the CALIBRATOR. The audio input is
reestablished, and now will modulate at the level
set with the calibrator.
ABOUT MODULATION METERS
•
The modulation depth meter on the 542APC
shows the modulation peak, with an integration
time that can be settled to values between 0 to
1 mS (default is 125 uS). By the other hand,
many transmitters have slow response meters.
In that case, the indication of both instruments
will be more similar the higher the peak density
of the audio.
•
In order that the modulation measurement on
the 542APC to be valid, the signal reception on
the receiver must be optimal.
3.8.1 About modulation peaks
The FCC (USA) recommendations for FM radio stations
are followed in many countries. Recommendation 73.268
indicates that the frequency modulation should be kept
as high as possible, but not exceeding 100% in frequent
recurrence peaks ("In no case is to exceed 100% on
peaks of frequent recurrence"). This indicates that in mo-
mentary (and not frequent) peaks can be exceeded the
100% of modulation staying within the legal framework.
The 542APC processor is designed to meet this FCC stan-
dard, allowing it to slightly exceed 100% on non-recur-
ring peaks. When adjusting the modulation, check the
regulations of your country.
When choosing and adjusting the audio processing pre-
sets, keep in mind if it is a single program for the whole
day; or whether the automatic switching by microphone
is activated, or by hourly range. In the first case, a com-
mitment adjustment must be used compatible with all
types of voices and music that the station handles. Auto-
matic switching of presets eliminates compromises as
each preset will be optimal for that type of music or
voice. This also reduces the auditory fatigue associated
with radio stations that use rigid processors, without
computed control.
3.8.2 Measures and improve the channel
separation
In an FM installation, the separation between channels in
the transmission is affected by the coupling of the set
coaxial cable - antenna. How much stereo separation lost
depends on the quality of the elements and its correct in-
stallation 1.
542APC includes pilot tone phase correction and gain ad-
justment for the module (L-R). It allow to compensate par-
tially the coupling of the transmission systems, improving
the separation of channels in the transmission.
To make the adjustment proceed as follow:
1. On the FM Monitor Analyzer screen, perform a
channel separation measurement. The higher the
value obtained in dB, the better the separation. If
the indication is greater than 40 dB (Excellent) it is
not necessary to make the adjustment.
The measurement of channel separation intro-
duces short audible tones on the air. It is neces-
sary that the station is correctly tuned so that the
measurements are valid (see 3.9 - FM analyzer
monitor).
2. On the screen STEREO GENERATOR, increase 0,1
dB the value “SUB(L-R) Adjust”.
3. Repeat the measurement for the channel separa-
tion and check if the value increased.
If instead of increasing decrease, go to the next
step (4).
If the separation increased, repeat point 2 by in-
creasing "SUB (L-R) Adjust" by 0.1 dB and checking
again if the channel separation continues to im-
prove. So on until it does not improve anymore.
4. If instead of increasing (improving) the channel
separation of the worst of the two values de-
creases, then REDUCE by 0.2 dB the value of "SUB
(L-R) Adjust".
5. Measure the channel separation again, verifying
that it has now increased. Repeat the operation in
steps of 0.1 dB until it no longer improves.
If the maximum channel separation obtained is not
"Excellent", the phase correction can be tested.
Change the "Pilot Phase" control in 0.5 degree
steps in one direction and in another to see if any
additional improvement can be obtained.
6. Once the best possible value has been achieved
(with good transmitters and antennas it should be
Excellent >40 dB) the setting must be saved in in-
ternal memory by pressing SAVE in the left menu.

No values better than -40 dB are measured because
above that value it has been shown that the ear (even
using headphones) is unable to perceive any improve-
ment in the sensation of stereo space.
Audio Processing Core - SOLIDYNE 542 APC Page 23