The beacon RX receives a satellite beacon signal which is down-converted to L-Band by a PLL stabilised
Low Noise Converter (LNC) at its L-band interface input. The beacon RX does not demodulate any satellite
because the satellite signals are sometimes CW signals but also very often modulated in FM or BPSK form.
Due to this fact the best implementation is a non-coherent receiver which measures the input level in a user
selectable defined bandwidth and provides this as a dB-linear and calibrated analogue output voltage and
digital information.
The level output is provided by three different and parallel available interface types: The RS232 interface
providing a bi-directional monitor and control protocol, the measurement data streaming output (RS422) or
the analog voltage output. The sat-nms beacon receiver is controlled remotely by a monitoring and control
application through the RS232 port. The RS422 streaming output sends the measured level at the full
measurement rate of the receiver with a minimal protocol overhead.
The following block diagram shows the functional blocks of the sat-nms L-Band Beacon Receiver.
The L-band input signal is applied to the SMA connector X1. The receive frequency range is from 950MHz
to 2050MHz. A small portion of the input signal is coupled out of the main signal flow, the coupling is
compensated by a small amplifier and this signal is provided as a L-band test output signal with the same
output level at the L-Band test output SMA connector with the same power level for test and measurement
purposes. The L-band signal is filtered within a 950 to 2050MHz filter and then attenuated by a
programmable attenuator in steps of 0dB, 10dB, 20dB or 30dB. After this programmable attenuator a first
amplifier with approximately 20dB of gain and a noise figure of 3.5dB amplifies the signal for the first down
conversion in a 13dBm mixer. This mixer converts the L-band input signal to the first IF of 765MHz by use
of a PLL frequency synthesiser. This mixer is highly linear and determines the overall dynamic range of the
system.
The 765MHz signal is then filtered by use of two 3-pol. ceramic filters which attenuates the out of receive
channel signals. After these two filter stages the 765MHz signal is converted by a second mixer to a 70MHz
IF by use of the fractional-N synthesiser. Direct behind the mixer a SAW filter with approximately 300kHz
bandwidth is used to filter the 70MHz signal. This filter has a very high Q so that only frequencies inside the
bandwidth will be fed to the last mixer circuit.
(C) 2020, SatService GmbH
www.satnms.com
LBRX-1MT-UM-2002 Page 17/21
