Ramsey Electronics FX-440 Manual page 71

STAGE A:
DC POWER INPUT REGULATION
&
DISTRIBUTION and PACKET RADIO 1/0
CONNECTOR
(J
1)
The •power supply" for your FX- transceiver is, basically, any "12-volt9
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 12-1 SVDC 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 •
+
BR" or •
+
8T", these are points where the
regulated
av
output is switched for Receive or Transmit by the PTT (push
to talk) circuitry (012, U4c, U4d, 013, 014) 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 US) operate from this single supply through the use of voltage
divider networks at the respective IC' s. The full 12-15 volt input is
1
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 1/0 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' II 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.
FX-440 Assm. 11