DANIELS
ELECTRONICS LTD.
TM
3-10
IM10-VR3H040-AB VHF Enhanced Extra Wideband Receiver Instruction Manual
3.3
Enhanced Synthesizer
3.3.1
Internal Power and Control (Digital Board)
Refer to "OS(R/T)-3(A/H) Digital Board Schematic Diagram" in section 6.13 of this manual.
The synthesizer operates from a +9.5 Vdc power source applied to connector pin P1-2. Total
current draw is approximately 160 mA for FM synthesizers and 65 mA for AM synthesizers.
POWER DOWN control line P2-4 controls the +5.0 Vdc microcontroller regulator U2 through
power MOSFET switch U1. For receiver applications the synthesizer is always ON, with the
enable line P2-4 directly connected to +9.5 Vdc. For transmitter applications, pin P2-4 is
controlled by MT-3 Transmitter Board jumper J18 which selects the synthesizer standby mode.
In Low Current Standby Mode, less than 14 mA current is drawn (for FM, < 4 mA for AM)
however, a delay of approximately 50 ms from PTT activation to transmitter turn is then
required to allow for synthesizer lock time. In Normal Mode, with the synthesizer ON
continuously, less than 10 ms delay is encountered. This capability comes at the expense of
additional standby current (160 mA for FM, 65 mA for AM).
3.3.2
Common Analog Board Circuitry
The Analog Board utilizes four optical receivers (U1 - U4) and one optical transmitter (U5) to
provide an isolated data interface to the digital board
.
In normal operating modes, +9.5 Vdc
Regulator IC U8 provides cont5.0 Vdc to the internal TCXO and power control optical
receiver U1. This results in a standby current level of
≈
14 mA for FM and 4 mA for AM
.
Primary power is controlled through activation of optical receiver U1 under control of the digital
board micro controller U4
.
Regulator U6 provides sw8.0 Vdc with regulator U7
providing sw5.0 Vdc to all analog supply points
.
Power MOSFET IC U9 works as a
clamping circuit to quickly discharge VCO filter capacitors C32 and C33 when powered down,
resulting in immediate suppression of RF output from the VCO.
The heart of the OS-3A/H Enhanced Synthesizer is U10 - a low power, single chip synthesizer
IC. A 9.6 MHz reference signal is provided either from the internal TCXO (JU1-B Analog
Board) or from an external source via SMB connector J1 with jumper JU1-A (Analog Board)
and jumper JU2 (AM Analog Board only) installed. The external reference source may be
9.6 MHz or 10.0 MHz and is selected via jumper JU2 on the Digital Board (9.6 MHz with JU2
not installed, 10.0 MHz with JU2 installed). If an external signal is used as the reference source,
it must be a sinusoidal, low phase noise, high stability signal of 0 dBm ±3 dB level. A poor
quality reference source will degrade receiver /transmitter performance to unacceptable levels.
Transistor Q2 forms a buffer amplifier having 50
Ω
input impedance at 10.0 MHz.