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BK Precision 4070A User Manual Rev.2.2
33
5.23 External BPSK Mode
Introduction
The External BPSK mode generates a phase shift keyed signal of fixed amplitude. The logic level on the Ext FSK
In connector is used as a modulating signal to shift the output phase between 0 and 180 degrees. The modulation is
suppressed carrier; i.e. no carrier energy is present in the output waveform.
NOTE: External BPSK is implemented by sampling the Ext FSK In line at 1.43 MHz. When a change in the state
of the line is detected, the output phase is switched. Since this input is sampled, there may be a small but
unpredictable delay between when the input changes and when the output phase is switched. This delay is never
greater than 1/1,430,000 sec (=700 nS). The net result is a 700 nS worst-case jitter in the modulation edges. The
faster you modulate the output, the more percentage of your modulating waveform this jitter becomes. Although you
can modulate beyond the stated maximum rate, this jitter becomes increasingly greater percentage of your
modulating waveform. The jitter becomes 10% of the high or low time at 35.75 KHz. This mode is available under
the “other” modes menu.
External BPSK Mode Parameters
The External BPSK mode has the following front panel display:
Figure 5.23-1: External BPSK mode display
1. Carrier Frequency
In this field enter the frequency of the carrier. You may enter from 0 Hz (DC) to 21.5 MHz in 0.01 Hz steps.
2. 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
0.1 dBm steps.
NOTE: The level specified is a 50O loaded level. This is the level of the signal, which will appear across a 50O
load connected to the SIG Out connector. Into an open circuit, the output swing will be twice the value entered.
Offset
By pressing this key, you can enter an offset voltage for the output waveform. For more information on output
offsets refer to section 4.4.
Ext FSK Input
Apply the digital data to be modulated on this connector. When this input is high, the output phase is advanced
180 degrees. When this input is low, the output frequency is retarded 180 degrees. (I.e. this input switches the sign
of the output carrier).
External BPSK
1,000,000.00 Hz - 10.0 dBm
2
1