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FORWARD–REFLECTED Switch & RF Power Meter.
The RF POWER METER, with its selector switch, allows monitoring parameters within the transmitter as
follows:
1. When switched to "FORWARD POWER", the meter indicates the RF power output of the STL–10A
transmitter. The maximum power is 10 Watts for the 850–960 MHz band (United States).
2. When switched to "REFLECTED POWER", the TEST METER indicates the amount of power returning on
the coaxial line from the antenna. This is useful in determining the VSWR (Voltage Standing Wave Ratio) for the
antenna system. The lower the VSWR for a given forward power, the better. Most antennas guarantee a VSWR
of less than 1.5 to 1.
The table below gives VSWR for various reflected powers:
Forward
Power
10 Watts (890–960 MHz)
10 Watts (890–960 MHz)
10 Watts (890–960 MHz)
10 Watts (890–960 MHz)
10 Watts (890–960 MHz)
PEAK MODULATION Meter.
A "peak–hold" twelve segment bar graph display is included on the STL–10A transmitter for setting and monitor-
ing peak STL modulation (composite or mono mode). The five highest LED's (100% to 250%) have a "peak–hold"
feature which will display an instantaneous peak value for one second. This is a valuable feature when dealing with
pre–emphasized program audio. The procedure for setting peak modulation is to adjust audio input level into the
STL–10A until the 100% bar is flashing on audio peaks. The 110% through 250% bars indicate over–modulation
and require a reduction in input level to obtain a 100% peak indication.
TEST Meter.
The TEST METER with its selector switch, allows monitoring of five important parameters within the transmitter
as follows:
1. "SUB LEVEL" – Indicates subcarrier injection. 0 VU is approximately 20% injection. For 10% injection use
–6 VU. Subcarrier voltage at J1 or J3 is approximately 1 volt for 20% injection, 0.5 volts for 10%.
2. "+13 VOLT SUPPLY" – Indicates regulated voltage supply operation. +1.5 VU is approximately 13.5 VDC.
3. "P.A. CURRENT" – The collector current of the final amplifier and its driver is calibrated to read "0 VU" on
the meter at rated power output and efficiency. The POWER ADJUST potentiometer should never be set to
produce a P.A. current greater than 0 VU.
4. "FORWARD POWER". The transmitter forward power level.
5. "REFLECTED POWER". The transmitter reflected power level.
Reflected
Power
0.3 watts
0.4 watts
0.5 watts
0.7 watts
1.0 watts
8
VSWR
1.40
1.50
1.57
1.70
1.90
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