Daniels Electronics OSR-3H061, Инструкция по эксплуатации

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IM10-OS3AH
406-470 MHz - Theory of Operation
64
The 9.6 or 10.0MHz reference source is divided
down to establish a channel selection step
size of 5.0/6.25, 12.5, or 25.0kHz. A third order
passive loop fi lter comprised of C37, C38, C39,
C45, C49, R36 and R32 is employed to achieve
the required noise performance, modulation
and worst case switching time of 50ms. A small
sample of RF energy is coupled from the VCO
output buffer U16 to the synthesizer IC U10
prescaler input (pin 11). FM modulation of
the VCO from approximately 100Hz to 3kHz
is achieved through the baseband input pin
P1-1 on the Digital Board. A 1kHz sine wave
with a level of approximately 400mVrms at
P1-1 provides FM deviation of 3.0kHz. SMB
connector J2 provides an RF output level
of approxi5dBm into a 50Ω load.
An optional low frequency modulation input
is provided through connector P1-18 on the
digital board, and routed to the analog board via
connector P3. This modulation input is coupled
to a low impedance DC coupled source. The
input provides a phase modulated bandwidth
from 0Hz (DC) to the PLL loop fi lter bandwidth.
This allows for specialized applications such
as paging or trunking where a separate low
frequency digital/analog modulation channel is
required. The phase modulation input on the
digital board, connector P1-18, is routed to the
transmitter’s audio processor pin P4-2 via JA4-2
on the MT-3 transmitter’s main board. It should
be noted that any application that uses the direct
TCXO modulation port transfers control of the
synthesizer’s steady state frequency setting to
the external modulation source. The internal
TCXO frequency control potentiometer RV1 is
then effectively removed from the circuitry.
A lock detect LED on the synthesizer’s analog
board (LED1) indicates an unlocked PLL
condition. An unlocked PLL condition normally
indicates that the VCO is not tuned within the
lock in range of the desired channel frequency.
In a transmitter, the loss of lock will prevent a
PTT from keying the power amplifi er module,
thus preventing the transmission of a spurious
output signal. Adjusting capacitor C24 will
normally re-establish a frequency lock within
the synthesizer’s frequency range. The optical
transmitter U5 on the analog board is also
activated in an unlocked condition and enables
the micro controller on the digital board to
respond to the unlocked PLL condition.
The UHF OS(R/T)-3H 406-470MHz synthesizer
employs an integrated surface mount VCO
module (U17) capable of full frequency band
coverage. Two VCO modules are used to
cover the 406-470MHz frequencies in the
Transmitter module, and one VCO Module is
used to cover the 427.4-451.4MHz frequencies
in the Receiver module. The VCO modules
are optimized for low phase noise, however
the transmitter VCO is additionally confi gured
with modulation input capability. PLL feedback
control voltage, at the output of the low-
pass loop fi lter, controls the VCO frequency
through pin 2, the modulation input (Mod
I/P) port. The PLL control voltage can range
b1.0VDC and +7.0VDC depending
on the selected operating frequency. External
baseband frequency modulation is provided
through connector P1 and VCO Mod input pin 6.
The PLL low-pass fi lter is formed by SELECT
components C37, C38, C39, C45, R32 and
R36. The loop fi lter response is optimized
for switching time, noise and modulation
requirements specifi c to each sub-band
within the 406-470MHz frequency range.
The SELECT components (including the
loop fi lter and VCO type) can be found in
tabular format on the UHF OS(R/T)-3H 406-
470MHz Analog Board Schematic diagram.
RF output power is taken from the VCO RF
output and amplifi ed/buffered by U11. U15
provides further amplifi cation and isolation
while delivering approxi10dBm to a
fi ve pole low-pass output fi lter formed by C53,
C58, C59, L11 and L12. The fi ve-pole low-pass
output fi lter, with a cutoff frequency of 530MHz,
effectively eliminates output harmonics.
SMB connector J2 provides interconnection
to the companion transmitter or receiver
with an output level of +5dBm ±2dBm.