Ramsey Electronics FX Series Manual page 60

STAGE A: DC POWER INPUT REGULATION & DISTRIBUTION and
PACKET RADIO I/O CONNECTOR (J1)
The "power supply" for your FX- transceiver is, basically, any "12-volt" battery
or well designed power supply operating from 120VAC or other source. In
theory, all "12V" sources should provide pure DC voltage to your FX-
transceiver DC input. In fact, there are many variations and imperfections in
common "12VDC" sources, ranging from weak batteries, poorly filtered AC
powered supplies, vehicle ignition noise, or just badly made power supplies.
Stage "A" of your FX- Transceiver is designed to help your radio survive
quite a wide variety of imperfections. It's not a "power supply" in itself, but it
comes close, because it performs all the essential functions expected from a
good solid-state DC source. Just add 12-15VDC from a battery, vehicle or
bench supply.
Much of the circuitry operates on the regulated 8 volts supplied by voltage
regulator VR1. If you have already looked around the schematic diagram and
also seen "+8R" or "+8T", these are points where the regulated 8V output is
switched for Receive or Transmit by the PTT (push to talk) circuitry (Q12, U4c,
U4d, Q13, Q14) which we'll discuss in more detail when it's time to build it in
Stage M.
The Receiver IC (U1) and the digital frequency synthesis circuit is powered by
+5 volts regulated by VR2. The op amps used in the circuit (U4 and U5)
operate from this single supply through the use of voltage divider networks at
the respective IC's. The full 12-15 volt input is supplied to the transmitter RF
output section and to the receiver audio amplifier (U2).
The large 1500 uf capacitor (C42) and inductor L20 are installed at the DC
input to filter out ignition noise, etc. Fuse F1 is contained in the power cord
and the DC power switch is integral to the volume control. The DC negative
(black) wire is soldered directly to the PC board ground plane.
The Packet Connector
The Packet I/O Jack (J1) is not a "stage" or section of your transceiver in
itself. It is simply a convenient "port," to use computer terminology, which
gives a packet TNC (terminal node controller) convenient access to the
microphone and receiver audio circuits. We'll install J1 and its associated
bypass capacitors at the beginning -- because now is as good a time as any,
and it gets some parts on your PC board quickly and easily! Also, having J1 in
place will give a little extra protection to other parts when you are working on
the solder-side of the board.