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from 40.955 to 70.455 MHz. This signal
is
brought through a fIlter and
AGe
controlled amplifier
stages to the second mixer.
The 40.455 MHz first IF
is
combined with the fIXed 40 MHz output from the second oscil-
lator synthesizer to produce a 455 kHz second IF. After amplification, this second IF
is
routed to the
plug-in 455 ,kHz filters which provides the main Receiver selectivity:
A second AGC-controlled amplifier follows before demodulation takes place. In the SSB/
CW / AM modes, a product. synchronous detector is used. In the CW mode, the BFO synthesizer may
be varied ±8 kHz (above 'or
~elow
the .155
kHz
c.enter frequency) through front panel controls. For.
FM
reception, the 455 kHz second IF is input to a limiting amplifier and subsequently to a separate
FM detector. A:ll three outputS from the synthesizers are referenced to an internal 5 MHz standard
frequency source, or to an external reference of 1 MHz. The demodulated signal is fed through an
audio crosspoint swit.:h to separate AF amplifiers which provide outputs for a 600 ohm line, a head-
phone jack, and an external loudspeaker.
For ISB operation, the optional ISB board provides the LSB signal path, while the main
IF / AF board provides the USB signal path. The LSB component of the 455 kHz second IF is processed
through similar circuitry with the common BFO synthesizer providing the remserted carrier for de-
modulation. A separate audio amplifier provides a 600 ohm line output.
All command signals, whether from the front panel controls or from an extended or remote
operating, position, are processed by the microcomputer assembly. Two separate buses carry control
data and address information to and from the microcomputer control assembly to the synthesizers for
frequency selection, and to the appropriate switching circuits controlling the different operating modes.
1.2
MECHANICAL CHARACTERISTICS
The RA6790/GM Receiver mounts in a standard 19-inch (48.3 cm) equipment rack, and
OCCUples 5,25 inches (13.33 cm) of vertical space, 19 inches (48.3 cm) wide, 18.5 inches (47 cm) deep
and weighs 30 pounds (13.5 kg).
A rigid, die-cast full width chassis is used as the base for the main frame of the Receiver.
~10unted
within compartments on the undersIde of this chassis are the mixer boards and the frequency
generation system. The input low pass fllter, main IF/AF,·optional ISB IF/AF and power supply
,
modules are'located on the top surfaces of the die-cast chassis while the control and digital I/O mod-
ules are attached on the Receiver main frame. All modules are accessible for maintenance and can be
removed or replaced using simple hand tools without the use of a soldering iron.
Manual controls and indicators for operation and monitoring of the Receiver are contained
on the front panel while input/output jacks and connectors are provided on the rear panel. A PHONES
jack. for audio connection to optional headphones. is contained on the front panel for convenient ac-
cess. A primary power fuse is accessible from the rear panel.
1.3
EQUIPMENT SUPPUED
The equipment supplied consists of the following:
1. RA6790/GM HF Receiver
2. WI8, Primary Power Input Cable
3. Connector, Mating for 13
1-2
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