Motorola APX 7000 Detailed Service Manual page 52

3-28 Theory of Operation: Transceiver Board
UHF2: The TX and RX VCOs used for UHF2 are contained in Y705 and Y704. To select the UHF2
RX VCO, pin 3 (SEL1) must be at a low logic level and pin 5 (SEL 2) at a high logic level, on Y704.
The UHF2 RX VCO output of Y704, pin 1 (POUT), is then fed to pin 4 (RF1) of switch U708. The
output of U708, pin 1 (RFC), then goes to pin 4 (RF1) of U709. The output of U709, pin 1 (RFC), is
then split into two signals. One to the prescalar buffer input and the other to the pre-buffer. The
output of the prebuffer is then fed to pin 1 (RFC) of U710. The output of U710, pin 5 (RF2) then goes
to the receiver section via TL_RX_LO transmission line.
To select the UHF2 TX VCO, pin 3 (SEL1) must be at a low logic level and pin 5 (SEL2) at a high
logic level, on Y705. The UHF2 TX VCO output of Y705, pin 1 (POUT), is then fed to pin 5 (RF2) of
switch U708. The output of U708, pin 1 (RFC), then goes to pin 4 (RF1) of U709. The output of
U709, pin 1 (RFC), is then split into two signals. One to the prescalar buffer input and the other to the
prebuffer. The output of the prebuffer is then fed to pin 1 (RFC) of U710. The output of U710, pin 4
(RF1) then goes to pin 4 (RF1) of U711. The output of U711, pin 1 (RFC) then goes to the transmit
injection buffer (comprised of Q842 and surrounding circuitry). The output of the transmit injection
buffer, then goes to the transmit section via the TL_TX_LO transmission line.
700–800 MHz: The TX and RX VCOs used for 700–800 MHz are contained in Y706 and Y707. To
select the 700 RX VCO, pin 5 (SEL2) must be at a high logic level and pin 3 (SEL1) at a low logic
level, on Y706. The 700 RX VCO output of Y706, pin 1 (POUT), is then fed to pin 5 (RF2) of switch
U709. The output of U709, pin 1 (RFC), is then split into two signals. One to the prescalar buffer
input and the other to the pre-buffer. The output of the prebuffer is then fed to pin 1 (RFC) of U710.
The output of U710, pin 5 (RF2) then goes to the receiver section via TL_RX_LO transmission line
To select the 800 RX VCO, pin 3 (SEL1) must be at a high logic level and pin 5 (SEL2) at a low logic
level, on Y706. The 800 RX VCO output of Y706, pin 1 (POUT), is then fed to pin 5 (RF2) of switch
U709. The output of U709, pin 1 (RFC), is then split into two signals. One to the prescalar buffer
input and the other to the pre-buffer. The output of the prebuffer is then fed to pin 1 (RFC) of U710.
The output of U710 (RF2) then goes to the receiver section via TL_RX_LO transmission line
To select the 700 TX VCO, pin 3 (SEL1) must be at a high logic level and pin 5 (SEL2) at a low logic
level, on Y706. The 700 TX VCO output of Y706, pin 1 (POUT), is then fed to pin 5 (RF2) of switch
U709. The output of U709, pin 1 (RFC), is then split into two signals. One to the prescalar buffer
input and the other to the pre-buffer. The output of the prebuffer is then fed to pin 1 (RFC) of U710.
The output of U710, pin 4 (RF1) then goes to pin 4 (RF1) of U711. The output of U711, pin 1 (RFC)
then goes to the transmit injection buffer (comprised of Q842 and surrounding circuitry). The output
of the transmit buffer, then goes to the transmit section via the TL_TX_LO line.
To select the 800 TX VCO, pin 5 (SEL2) must be at a high logic level and pin 3 (SEL1) at a low logic
level, on Y706. The 800 TX VCO output of Y706, pin 1 (POUT), is then fed to pin 5 (RF2) of switch
U709. The output of U709, pin 1 (RFC), is then split into two signals. One to the prescalar buffer
input and the other to the pre-buffer. The output of the prebuffer is then fed to pin 1 (RFC) of U710.
The output of U710, pin 4 (RF1) then goes to pin 4 (RF1) of U711. The output of U711, pin 1 (RFC)
then goes to the transmit injection buffer (comprised of Q842 and surrounding circuitry). The output
of the transmit injection buffer, then goes to the transmit section via the TL_TX_LO line.
To select the 7/800 TX VCO, pin 5 (SEL2) must be at a high logic level and pin 3 (SEL1) at a low
logic level, on Y707. The 7/800 talk around VCO output of Y707, pin 1 (POUT), is then fed to pin 8
(RF3) of switch U709. The output of U709, pin 1 (RFC), is then split into two signals. One to the
prescalar buffer input and the other to the pre-buffer. The output of the prebuffer is then fed to pin 1
(RFC) of U710. The output of U710, pin 4 (RF1) then goes to pin 4 (RF1) of U711. The output of
U711, pin 1 (RFC) then goes to the transmit injection buffer (comprised of Q842 and surrounding
circuitry). The output of the transmit injection buffer, then goes to the transmit section via the
TL_TX_LO line.