Earlier this evening I performed a few tests with "
Oscar".
Following the details shown at "
Check Send", the send and receive wires (blue and red, respectively) were connected together and the unit was switched to "
Meas Term/Send 0dB". Unfortunately my unit appears to be out of calibration. Instead of seeing 0dB +- 0.25dB, I observed +2.01dB. So either the send circuit or the receive circuit (or both) requires some adjustment.
Hmm . . .Inserting a decade resistance box (
Rheostat No 1A) between the send and receive wires showed that a series resistance of 380 ohms brought the display back to 0.00dB.
Next, the
Oscar's send circuit was connected to the
Level Measuring Set No 35A and with the latter configured to provide a 600 ohm termination, it showed +1.8dB.
Now I am uncertain of the calibration status of the
LMS No 35A . . . but perhaps the
Oscar's send circuit should be adjusted so that 0.0dB is displayed on the
LMS and then the receive circuit should be adjusted so that
it (the
Oscar) displays 0.00dB when the send & receive wires are connected together.
Ideally I would need sight of the circuit diagram and the calibration instructions (or the maintenance manual) for the
Oscar unit.
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