BNC 630 - Manual (Page 10)

5
3.
External Modulation In connector
The External Modulation In connector, located on the rear of the 630, accepts an external analog signal as illustrated here:
Figure 2.0-3: Connecting an external signal
On this connector, the user supplies a baseband signal (below 50 KHz) that is used to modulate an output carrier. (A microphone
is shown here as an example). It also serves as the input connector for DTMF signals in DTMF Detection mode, and signals to be
measured in the Power Level and Voltage Measurement mode.
This input is high impedance (about 30K ohms). It was made high impedance to avoid loading down the circuit supplying the
signal.
This input is DC coupled within the 630. The signal on this input is internally lowpass filtered to a cutoff frequency of 50 KHz.
The input level for this connector is ±5V max. For external modulation modes, a 1V p-p signal will fully modulate the carrier. If
you apply a higher level signal than 1 Vp-p, the input signal will be distorted. The distortion that will take place under these
conditions is a "hard limiting" type (i.e. the waveform will "flat top" at the positive and negative extremes). Under these conditions,
the word "Overld" will be printed to the LCD for input levels that are too high.
*** Caution ***
Levels outside the ±25 V range on this input may damage the 630.