BNC 630 - Manual (Page 21)

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5.3 External AM Mode
Introduction
The External AM mode generates an amplitude modulated signal of fixed carrier frequency. An externally-supplied signal on the
Ext Mod In connector is used as a modulating signal to vary the amplitude of a carrier sinusoid. The modulation waveform is not
suppressed carrier; i.e. a fixed amount of carrier power is always present in the modulated signal.
External AM Mode Parameters
The External AM mode has the following front panel display:
Figure 5.3-1: External AM mode display
1. Input Gain
In this field specify a value used to scale the input signal. With a value of .999, a 1 Vp-p signal on the input will result in 100%
modulation of the carrier amplitude. You may enter a value from 0 to .999. (The gain value is always less than 1.0).
To enter a value, type 1 to 3 numeric digits. If you type 3 digits, the value is automatically entered. If you only type 1 or 2 digits,
you can press the MHz key or the KHz key or the Hz key (all are equivalent) to enter the gain value.
2. Carrier Frequency
In this field enter the frequency of the carrier, from 0 Hz (DC) to 21.5000000 MHz in .01 Hz steps.
3. PEP Level
In this field enter the output level, from 4 mVp-p to 10 Vp-p in 1 mV steps or from -44.0 dBm to +24.0 dBm in .1 dBm steps.
NOTE: The level specified in External AM mode is the Peak Envelope Power, or PEP. As a peak-to-peak value, this level
represents the maximum peak-to-peak voltage swing that will result from a 100 percent modulated carrier. If no modulating signal
were applied, the unmodulated carrier would have only half the peak-to-peak swing of a 100% modulated carrier.
NOTE: The level specified is a 50 ohm LOADED level. This is the level of the signal which will appear across a 50 ohm load
connected to the SIG Out connector. Into an open circuit, the output swing will be twice the value entered.
Offset
You can enter an offset voltage for the output waveform. For more information on output offsets refer to section 4.4.
Ext Gating Input
(rear panel connector)
This TTL compatible input can be used to gate the output signal on or off. A logic high voltage turns off the output.
For further information on the Ext Gating Input, refer to section 2.0.
External AM Input gain: .999
20,000,000.00 MHz PEP level: -10.0 dBm
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