Laird Controls North America Inc. 86942 사용자 설명서
9S21-8694-A001
Laird™ proprietary and confidential
Page
9 of 12
Revision: A, Approved
2.3 Frequency Reference and Phase Locked Loop:
The overall RF system frequency reference is provided by a 14.4 MHz VCTCXO (designator Y4).
The synthesizer uses an external VCO (designator U6) that is tunable from 425 to 475 MHZ.
The nominal RF output level of the VCO is nominally between +2 and +6 dBm into 50 ohms.
The RF output of the VCO is subsequently split using resistive dividers into:
1. RF Sample input for the PLL
2. 1
2. 1
st
RX Mixer LO input
3. TX signal input to the TX Amplifier chain.
2.4 Receiver Section:
The RF input to the Receive section is provide using one of the existing ANT1, 2, 3 input, these are selected using
signals provided by the Microcontroller (designator U5).
signals provided by the Microcontroller (designator U5).
The received signal is the routed to a UHF SAW filter FL1 that has a width of about 20MHz and is centered in one
of the designated RX bands:
of the designated RX bands:
Low Band – 406 to 425 MHz
Mid Band – 425 to 447 MHz
High Band – 447 to 475 MHz
These filters are installed depending on the RX Band variants that are being used.
The Local Oscillator input is supplied by an output of the splitter mentioned above referring to the VCO.
The 21.4MHz mixer signal output is filtered using a crystal Filter (designator Y1), the BW of this filter is selected
depending on the product variant built (either a narrow or a wide band version).
depending on the product variant built (either a narrow or a wide band version).
After filtering the 21.4 MHz signal is routed to an FM IC that performs an additional frequency down-conversion
to 455kHz and provides a second mixer and 2
to 455kHz and provides a second mixer and 2
nd
LO oscillator using and externally supplied crystal (designator
Y2).
The FM IC SA605 (designator U2) additionally provides limiting IF gain and quadrature detection as well as
having outputs for RSSI monitoring besides the demodulated signal.
having outputs for RSSI monitoring besides the demodulated signal.
The second IF Filtering is provided using two 455kHz Ceramic Filters 455FU (455DU) (designators FL3 and FL4).