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F800 CIRCUIT DESCRIPTION
13 (25)
Uppgjord (även faktaansvarig om annan) -
Prepared (also subject responsible if other)
Nr
-
No.
KL/ECS/S/LT Magnus Lindahl
ECS/S/LT-96:5044
Dokansv/Godk -
Doc respons/Approved
Kontr
-
Checked
Datum
-
Date
Rev
File
KI/ECS/S/LTC
1996-06-06
A
965044.DOC
Antenna switch
The antenna switch is only implemented in simplex versions of the F800 radio board.
The antenna switch is an electrical switch implemented with diodes and one transistor.
The switch is followed by a LP filter at the antenna output. At the RX input there is a
matched LC filter with one capacitance diode and one pin diode. In the TX path there
is a pin diode acting as a switch. As soon as the transmitter is activated the transistor
starts feeding a current through the diodes and thus the TX RF path is opened and
the impedance of the filter on the RX input is changed. To protect the RX front end the
tunnel diode is also connected to the front end input to ground when the transmitter is
active. To insure that the antenna switch has changed from receive mode to transmit
mode before the TX signal is connected to the antenna there is a short delay, 1 mS, in
the power control loop. The antenna switch is controlled by the RX/TX signal from the
CPU board.
LP
Filter
From TX
To RX
12VSW
10VT
Fig H: Antenna switch