Belar: "When accuracy counts, count on Belar"



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-2.

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.


RF Sensitivity 				100 uv. across 50 ohms

Antenna Required			Whip or Loop

Bandwidth 				0.2 dB 10 kHz

                                  	-3 dB 16 kHz

                    			Greater than -40 dB 40 kHz

I.F					260 kHz

IMAGE REJ 				Greater than 50 dB

IF REJ 					Greater than 50 dB

RF OUTPUTS				260 kHz for MODULATION measurements, 5 volts RMS min. STATION FREQ  for FREQ measurements

AGC Range     				Less than 2% change in carrier level 

                                           for 12 dB change in input level

Size					3.5"H x 19"W x 11.5"D

Net Weight 				8 lbs.

Shipping Weight				11 lbs.

© Copyright 2012 Belar Electronics Laboratory, Inc. All rights reserved. Specifications subject to change without prior notice.

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