BK Precision 4070A User Manual Rev.2.2
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3. External Modulation In connector The External Modulation In connector, located on the rear of the 4070A, accepts an external analog signal as
illustrated here:
Figure 2.0-3: Connecting an external signal
On this connector, the user supplies a base band signal (below 50 KHz) that is used to modulate an output carrier.
(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 30KO). It was made high impedance to avoid loading down the circuit
supplying the signal.
This input is DC coupled within the 4070A. The signal on this input is internally low pass filtered to a cutoff
frequency of 50KHz.
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.
External signals greater then ±25Vp-p range on external applied to modulation input may damage the 4070A.