The Belar RFA-2 AM RF Amplifier is a selective, high gain, all solid state AM RF Amplifier/Down Converter with automatic gain control (AGC). As a companion to a Belar AM Modulation monitor, the RFA-2 makes it possible to monitor off-the-air AM signals accurately and conveniently without the problems associated with changes in transmitter power level, antenna patterns, and signal fading. The RFA-2 allows monitoring of both carrier frequency deviation and modulation characteristics from a point remote from the transmitters in the 530-1710 kHz band. Note that the RFA-2 has an IF output and is suitable only for use with a Belar AM Modulation Monitor, such as the AMM-2B, AMM-3, or AMMA-1.
The RFA-2 uses both crystal controlled superheterodyne and heterodyne repeater principles to provide a virtually distortionless, spurious free output for modulation monitoring and a frequency restored output for frequency monitoring.
The intermediate frequency (IF) of the RFA-2 is 260 kHz whereby a precision 30 kHz wide band-pass filter is used to remove the unwanted adjacent channels and still retain the full frequency response and linearity for accurate monitoring of 10 kHz modulating frequencies. The IF is amplified by a linear, feedback amplifier whose output then drives the modulation measuring portion of the AM monitor. There is a 6 dB margin in the output capability to permit the high positive peaks of supermodulated carriers to be accurately monitored.
A portion of the 260 kHz is fed to a limiter to remove modulation and is mixed with the local oscillator frequency to restore the original station frequency. The output is filtered to remove unwanted signals and is amplified to provide a frequency measuring output
The outstanding feature of the RFA-2 is the AGC range-the total range is more than 30 dB. Sufficient feedback is employed to hold the output level constant to better than 2% for an input level change of 12 dB. This eliminates the problems encountered by station’s having to change power levels or antenna patterns. The AGC also holds the level constant in remote locations where signal fading is a problem.
100 uv. across 50 ohms
Whip or Loop
0.2 dB ±10 kHz
-3 dB ±16 kHz
Greater than -40 dB ±40 kHz
Greater than 50 dB
Greater than 50 dB
260 kHz for MODULATION measurements, 5 volts RMS min. STATION FREQ for FREQ measurements
Less than 2% change in carrier level for 12 dB change in input level
3.5″H x 19″W x 11.5″D
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