BNC 630 - Manual (Page 42)

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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. To enter the External BPSK mode, press Mode, Clear, 1, 2
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 21.5000000 MHz in .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 .1 dBm steps.
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
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
(rear panel connector)
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).
Ext BPSK
20,000,000.00 Hz -10.0 dBm
1
2