Optimod-AM 9400 V1.2 Operating Manual - Orban

OPTIMOD-AM DIGITAL INSTALLATION 2-31
11. Test the equipment downstream from OPTIMOD-AM.
Test the RF envelope at the transmitter’s output to determine if it exhibits tilt,
overshoot, or ringing. If you observe these problems, you can often adequately
equalize it them with the 9400’s transmitter equalizer, whose settings are determined
by the on-air Transmission Preset.
Dealing with tilt and overshoot may seem fussy, but every dB of tilt or overshoot
is a dB of loudness lost!
Use the 9400's built-in square wave generator to make this test:
A) Navigate to SETUP > TEST.
B) Set the TONE MOD to 0%.
C) Set the MODE to SQUARE.
D) You may now turn the final amplifier on. Observe the RF envelope at the
common point with a DC-coupled oscilloscope and advance the TONE MOD
control until you can easily see the shape of the square wave.
Sweep the TONE FREQ control from 125 to 1000 Hz and observe the shape
of the square wave as you do so. If you are driving more than one transmitter
and/or your antenna load changes between day and night, test all
combinations that you will be using.
If the square wave is free from tilt and ringing at all frequencies in the
sweep, you do not need to set up the transmitter equalizer in steps 12
through (13.H)a) below. Otherwise, you must do so to achieve the highest
loudness and coverage that your facility can produce.
If you observe problems with some combinations of transmitter and load
but not others, record which combinations cause problems. You will only
need to set up set up the Transmitter Equalizer for these combinations.
You will dedicate one Transmission Preset for each problematic combination
so that each combination can be equalized independently.
Figure 2-9 on page 2-33 shows tilt and Figure 2-11 on page 2-35 shows
ringing.
Caution: To avoid damaging the transmitter, do not exceed 50% modulation
with square waves.
Important: Do not place additional clipping devices after OPTIMOD-AM! The
additional distortion introduced by these devices will totally nullify the advantages
of OPTIMOD-AM's distortion-canceling clipper and will cause the out-ofband
energy induced by clipping to violate FCC or ITU-R standards.
12. Equalize the transmitter’s low frequency square wave response.
[Skip the Transmitter Equalizer adjustment steps [(steps 12 though (13.H)a)] if
the RF envelope square wave test you preformed in step 11 above showed no
sign of tilt, overshoot, or ringing.]