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4.4 The integrated matching system - attenuating and amplifying
4.4.1 The importance of matching
Sometimes in systems with two antennas one of them has a much longer connection cable for receiving and transmitting. So the
signal from the antenna with the longer cable has a higher attenuation than the other one, which leads to different power levels
at the inputs of the traffic modem and the TX input of the antenna.
Furthermore it is normal that antennas have different output power levels as well as input sensitivities, even if they are struc-
turally identical. This can cause errors like short lockouts of the traffic modem or over powering the transceiver. To match these
different power levels, the VSAT DivKit has four power regulators attenuating from -15dB to amplifying to +15dB: one for each
RX line and one for each TX line. You can adjust the power levels in a resolution of 16 steps of 2dB each, where "0" corresponds to
15dB amplification and 16 corresponds to 15dB attenuation. The following examples describe situations where it is necessary to
use the power regulators.
Explanation: Fig. 4 shows an example of mismatching RX power levels. Antenna 1 has an RX power output level of about -30dBm
and antenna 2 has an RX power output level of about -20dBm.
Antenna 1 is currently online. When the VSAT DivKit switches to antenna 2, the power at the modem suddenly jumps from -30 to
-20 dBm. Because the modem has to re-adjust its tuner for the new input level, the connection to the network will be intermittent
for a short time. In this example, the power regulator switches for RX1 of the VSAT DivKit needs to be adjusted to 10dB attenuati-
on to match the power level of the antenna 2.
Now both RX levels have -30dBm at the modem input.
Fig. 4: Example for the mismatching power levels of RX at the inputs of the modem.
ACU 2
EPAK DIVERSITY KIT
Modem
ACU 1
RX power: -30dBm
RX power: -20dBm
TX1
RX1
TX2
RX2
TX1
RX1
TX2
RX2
No matching at power regulators
TX
RX
arrriving power level:
-20dBm for RX2
-30dBm for Rx1
Antenna 1
Antenna 2
