Note
Probably designed mostly with the CB market in mind, it certainly found its way into ham shacks.
The Libra 631 is an analog test center featuring a triple-meter interface that provides real-time data on transmitter health and signal quality. One of its standout features is the ability to monitor all transmitter functions—including power output, Standing Wave Ratio (SWR), and modulation—at the same time.
The unit is designed to be installed at any point within a transmitter line using standard RG/58BU cabling. It is primarily intended for use with A.M. transmitters, though specific precautions are noted for use with Grounded Grid amplifiers to ensure accurate modulation readings.
Specifications
Power Measurement Range: 1 to 1000 Watts
RF Power Scales: 10, 100, and 1000 Watts
Connection Type: SO-239
Modulation Type: AM Modulation
Meter Protection: To prevent damage to the sensitive meter movements, users should always set the RF Range Switch to the highest setting (1000W) when the power output is uncertain.
Calibration: SWR and Modulation functions must be re-calibrated whenever the wattage range is changed to avoid damaging the unit.
Grounded Grid Amplifiers: Because feed-through power prevents these amplifiers from reaching 100% modulation in AM mode, it is recommended to check modulation at the transmitter or while the amplifier is in standby.
