User Manual

SECTION 1: THEORY OF OPERATION
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the VCO, canceling out most of the modulation. The output from the jumper block goes to the 10 MHz
reference via REFMOD.
The VBIAS input is a 2.5-volt DC source, which biases the op amps to the correct operating point. It is
generated by modem chip (U14) on the System Controller Board.
Phase Locked Loop
This section displays phase locked loop (PLL) circuitry. The 10-MHz reference (Y1), runs synthesizer
(U2), which in turn controls VCO1. The main section of this board is the synthesizer chip (U2). The
device contains the key components of a PLL, including a 1.1 GHz prescaler, programmable divider, and
phase detector.
In operation, the desired frequency is loaded into U2 as a clocked serial bit stream via the CLK and
DATA/I inputs. The lock detection circuitry consists of inverters U6A and U6B, diode CR1, and resistor
R1. When the synthesizer is in lock, the LD pin on U2 is high, making the EXCLD output on terminal
block (TB1) high. The EXCLD output on TB1 routes the lock detect output from the Exciter Board. This
configuration tells the CPU on the System Controller Board that it is acceptable to process received data,
or to key the transmitter when LD is high. Otherwise, if a fault in either synthesizer prevents a lock,
receive and transmit operation will be inhibited.
The switch (JMP1) is used to select the supply voltage to chip U2. The UHF injection signal is generated
by module VCO1. This device is a wide-range voltage controlled oscillator (VCO). A voltage on the VT
input determines the VCO frequency. The voltage is generated by the phase detector output (PD/O) of
U2, which drives a loop filter consisting of R19, C16, C17, and C47. The filter integrates the pulses,
which normally appear on PD/O into a smooth DC control signal for the VCO. The output of VCO1 is
attenuated by module AT2, resulting in improved VCO stability.
Amplifier U8 amplifies the signal and applies it to a splitter (U3). One output of U3 is connected to a
switch (U1). U1 is enabled by signal TX when the transmitter is enabled. The other output of the splitter
is connected through AT1 and provides feedback to U2.
Power Amplifier
The transmit injection signal from the RF injection section is applied to the high-powered linear amplifier
(U1) one (1) watt amplifier. The signal is then routed to the final power amplifier boosting the output
signal to 40 watts. The output of the amplifier is routed to transmit antenna port ANT1 (via SW1).