Watkins-Johnson Company WJ-8718-19/FE Instruction Manual page 87

CIRCUIT DESCRIPTION WJ-8718-19/FE HF RECEIVER
a. VHF Input - The VHF input is a broadband 30-100 MHz RF
signal sent from the Input Switching Section.
b. IF Output - The IF output is a 29.5 MHz IF signal sent to the
Input Switching Section.
d. 1 MHz Ref. - The Synthesizer Section sends a 1 MHz square
time base signal to the Frequency Extender Section.
e. Tuning Data - Tuning Data is sent from the Digital Control
Section and consists of a 7-bit tuning word, 2-bit band select
word, RF switch control and an analog tuning voltage.
3.2.3 RF/IF CONVERSION SECTION
A general description of the RF/IF Conversion Section functions and signal
interfaces is provided in the following paragraphs.
3.2.3.1 RF/IF Conversion Section Functions
The RF/IF Conversion Section performs the following functions:
a. Frequency Translation - The incoming 0.005-100 MHz spectrum
is converted to 10.7 MHz (2nd IF) by a double conversion
process with a 1st IF center frequency of 42.905 MHz.
b. Bandlimiting - The bandwidth of the 10.7 MHz 2nd IF output is
limited to 50 kHz and is characterized by low in-band ripple
and group delay.
c. Gain Control - Under high RF input signal conditions, the
overall gain of the RF/IF Conversion Section is reduced to
prevent overloading or saturation of succeeding receiver stages.
3.2.3.2 Input/Output Signal Interfaces
The following input/output signals interface with the RF/IF Conversion
Section:
3-4
a. RF Input - Rear panel FE-A2J1 feeds broadband 0.005-100 MHz
RF signals from an antenna or similar source into the receiver
at a 50 ohm impedance.
b. 1st LO - The Synthesizer section sends the 1st LO signal,
42.91-72.90 MHz to operate the 1st mixer.
c. 2nd LO - The Synthesizer Section sends the 2nd LO signal,
32.31000-21.20001 MHz, to operate the second mixer.