Instruction Manual

DE
DANIELS
ELECTRONICS
Enhanced AM/FM Synthesizer Instruction Manual OS(R/T)-3(A/H) 29 - 470 MHz 2-1
2 THEORY OF OPERATION
2.1 Internal Power and Control (Digital Board)
Refer to "OS(R/T)-3(A/H) Digital Board Schematic Diagram" in section 4 page 19. The
synthesizer operates from +9.5 Vdc applied to connector pin P1-2. Total current drain is
approximately 160 mA (65 ma for AM). Power Down control (P2-4) controls the +5.0 Vdc
microcontroller regulator U2 through power MOSFET switch U1. For receiver applications, the
synthesizer is always operating with the enable line P2-4 permanently connected to +9.5 Vdc. In
transmitter applications, pin P2-4 is controlled by MT-3 Transmitter Board jumper J18 which
selects the synthesizer's standby mode. In low current standby mode (< 16/4 mA) approximately
50 ms of transmitter turn on delay from PTT activation must be tolerated (lock time of
synthesizer). For transmitter applications requiring less than 10 ms of turn on delay, the
synthesizer can be made to run continuously. This capability comes at the expense of an additional
160 (65 mA for AM) of transmitter standby current.
2.2 Synthesizer Analog Circuitry (Analog Board)
There are four separate analog circuit boards covering the four frequencies bands of 29 - 50 MHz,
118 - 159.4 MHz, 128 - 174 MHz and 406 - 470 MHz respectively. All four analog boards are
similar in operation and circuit topology with the VCO, Loop Filter, and Output Lowpass Filter
sections being band specific. Refer to "OS(R/T)-3(A/H) Analog Board Schematic Diagram” in
section of this manual.
2.2.1 Common Analog Board Circuitry
This section describes the circuitry common to all versions of the FM Synthesizer Analog Board.
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 continuous +5.0 Vdc to the internal TCXO and power control optical
receiver U1. This results in a standby current level of ≈ 10 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 switched +8.0 Vdc with regulator U7 providing
switched +5.0 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 OS-3H enhanced synthesizer is formed around a low power, single chip MC145190
(MC145191) synthesizer IC U10. A 9.6 MHz reference signal is provided from either the internal
TCXO (JU1-B Analog Board), or an external source via SMB connector J1 with jumper JU1-A