Subject to Export Control, see Cover Page for details. 1-11
H. RF Assy (62A1A3) (Figure 1-6) (cont)
When the T/R Connector is selected, the signal is routed through a 20 dB high power attenuator.
This attenuator allows the T/R Connector to accept signal levels up to 20 W directly into the Test Set.
A temperature sensor mounted next to the attenuator is monitored by software. If the temperature
rise is too great, the operator is alerted. Following the attenuator are resistive splitter feeds, part of
the received signal to the power detect circuit. The power detect circuit is a diode detector used to
measure the input power for the Power Meter function. The resistive splitter also feeds the signal
through a 10 dB pad to the receive connector selection switch.
When the ANT Connector is selected, a signal input to the ANT Connector passes through the
protection circuitry to the receive connector selection switch. From this point on both the ANT and
T/R Connectors share a common path. The signal is input to the step attenuator that provides 0 to
30 dB of attenuation in 10 dB steps. Following the attenuator part of the signal is tapped of to feed
the log amp detector. The detected level out of the log amp is used to insure that the receiver does
not go into compression.
The received signal passes through a low-pass filter to remove out-of-band signal to the switchable
pre-amp. The pre-amp is selected by software to increase sensitivity for low-level signals. The
signal is then input to a mixer where the signal is mixed with the Receive 1st LO. The LO is tunable
from 1405 to 2403 MHz to produce an IF signal at 1403 MHz. The IF signal is filtered to remove
unwanted mixing products and amplified before being input to a second mixer. The signal is then
mixed with the Receive 2nd LO of 1310 MHz to down-convert the signal to a 93 MHz IF. The 93 MHz
IF is amplified and filtered then input to the 3rd mixer. The signal is mixed with the Receive 3rd LO
of 80 MHz to down-convert the signal to the final IF of 13 MHz. The IF then passes through a low-
pass filter and an amplifier before being input to a switchable filter network. At this point the signal
either passes through a 1 MHz wide bandpass filter or a 3 dB pad that compensates for the insertion
loss of the filter. Following the switchable filter, the signal then passes through several selectable
gain amplifiers before being output to the Multi-Function PCB Assy for digital processing. The
amplifiers are selectable in gain increments of 10 dB and controlled by the AGC software.
To Next Page
Loading...
