300 Welsh Road Building 3 Horsham, PA 19044-2273 URL: http://www.gdpspace.com
Phone: 215-657-5242 Fax: 215-657-5273 E-mail: gdpinfo@gdpspace.com
ENCODER MODULATOR
Model 785
Features
General Description
The Model 785 Encoder Modulator
Unit (EMU) accepts four (4) input
channels. Data and clock inputs are
RS422 signal levels. The RS422
input signal levels are converted
internally to TTL and the clock
symmetry corrected for each channel.
The TTL data and clock signals are connected to PSK006
BPSK Subcarrier Generator modules. The data is
convolution encoded and a BPSK subcarrier is modulated
with the encoded data stream. A selection is provided of
an internal PRN data source for BPSK subcarrier
modulation. Each modulator output level is adjustable
from approximately +2 to +8 dBm into 50 Ohms.
Modulation data and clock, and a fixed level modulated
subcarrier are also provided as outputs at the rear panel
interface. Modulation can be turned off to provide a continuous wave (CW), sinusoidal
subcarrier output. The subcarrier modulators can provide BPSK and QPSK modulation,
where QPSK is an option.
The RS422 levels of the input clock & data signals are converted to TTL levels suitable for
driving the BPSK modulators. In addition, any departure in the input clock duty cycle from
the ideal 50%/50% duty cycle is corrected in order to ensure the waveform quality of the
convolutionally encoded data. The four (4) BPSK subcarriers are applied to a linear signal
Summer. The individual signal amplitudes are controlled to create a composite signal with
appropriate component power levels. The composite signal level is adjusted prior to its
application to a Phase Modulator.
The phase modulation can be
turned OFF to provide a 12 MHz
CW carrier. The phase modulated
carrier is upconverted to 70 MHz.
The output level of the 70 MHz IF
PM carrier is programmable over
a 20 dB range. The 70 MHz
output is connected to the rear
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