4.1 - 12
MTP700 Portable Radio / Detailed Service Manual
TRANSCEIVER 400 MHz
IF Filter
The IF signal is routed via the IF filter (FL2500), which has an insertion loss of 2 dB and
attenuates unwanted mixing products of the mixer. It is connected via a matching net-
work, consisting of C2502, L2501 and C2503, to the balun network.
Balun
The balun network (L2502, C2505, C2504 and L2503) transforms the single-ended input
RF signal to a differential double-ended output.
The differential signal is routed to the WPIC, pins A4 and B4, via C1018 and C1019.
WPIC (Receiver Back End Section)
The differential IF signal is amplified and converted down to zero IF inside the WPIC
(World Phone IC) by the 2nd LO signal. The 2nd LO signal is routed to the WPIC at pin
D1 and divided by two into the quadrature generator block of the WPIC. The baseband
signal from this 2nd mixer passes to an amplifier baseband filter array. The amplified and
filtered signal is passed to the WPIC A/D converter. This A/D converter digitises the ana-
log differential signal into its I and Q components. The I and Q components appear in
sequence on the WPIC_SRD line whenever the RX_ACQ line is high. The WPIC_SRD
data is clocked into the DSP using a clock signal (WPIC_TXCLK) from WPIC. The WPIC
is controlled via SPIA_MOSI, SPIA_CLK and SPIA_CSO_WPIC from RedCap2.
An internal AGC that is controlled by a control unit, establishes an appropriate attenua-
tion for unwanted signals as well as an appropriate gain for wanted signals. The voltage
at external capacitor C1008 indicates the AGC attenuation level for the different input sig-
nal levels. The voltage at the capacitor varies from 1.4V to 2.7V as a function of the
power of the received signal.
Содержание IMPRES Tetra MTP700
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