1-10 Subject to Export Control, see Cover Page for details.
H. RF Assy (62A1A3) (Figure 1-6)
The RF Assy consists of the RF Converter PCB Assy and the RF Controller PCB Assy. The RF Assy
receives power and control via the Multi-Function PCB Assy.
The RF Converter PCB Assy contains the RF termination for the T/R Connector, ANT Connector and
SWR Connector, as well as the frequency translation circuitry and step attenuator for both the
receive and generate paths. The RF Controller PCB Assy interfaces directly with the Multi-Function
PCB Assy to control the RF Assy. The RF Controller PCB Assy contains the 80 MHz TCXO system
clock and the RF synthesizers that generate the required Local Oscillator (LO) signals.
An 80 MHz TCXO with a stability of 1 ppm provides the reference signal for the RF Assy as well as
the Multi-Function PCB Assy. The 80 MHz TCXO provides the reference signal to the five Phase
Lock Loops (PLL) used to generate the required Local Oscillator (LO) signals.
The Generate path of the RF Assy receives a 10.5 MHz IF signal from the Multi-Function PCB Assy.
This signal is mixed with the 80 MHz Gen. 3rd LO to create a 69.5 MHz IF that is filtered to remove
unwanted mixing products and amplified before being input to the Generate leveler circuit. The
Generate leveler circuit is used to set the desired output signal level by compensating for variations
in flatness over the 2 to 1000 MHz output band. The 69.5 MHz IF is then mixed with the 1330 MHz
Generate 2nd LO to produce a 1399.5 MHz IF. The output of the mixer is filtered to remove unwanted
mixing products and amplified before being input to the last mixer. The Generate 1st LO, which
covers 1401.5 to 2399.5 MHz, is mixed with the 1399.5 MHz IF to produce an output frequency of 2 to
1000 MHz. Following the mixer the signal passes through a low-pass filter and into an amplifier. The
output of the amplifier is tapped off to the Generate Level detector. The output of the detector is
feed back to the Generate Leveler to level the generate system. The RF signal out of the amplifier
then passes through the step attenuators. The step attenuators provide 60 dB of attenuation in 1 dB
steps to set the signal level out of the Unit. The signal is then input to a RF switch. One port of the
switch goes to the T/R Connector via a 3 dB pad, 3 way resistive splitter, and the 20 dB power pad.
This attenuator allows the T/R Connector to accept signal levels up to 20 W directly into the Test Set.
The other port of the RF switch is input to a second RF switch which steers the signal to either the
ANT Connector or the SWR circuit. When the ANT Connector is selected, the signal passes through
another RF switch to insure sufficient isolation and is coupled to the ANT Connector through the ANT
Connector protection relay.
Connected to the ANT and SWR Connectors are the connector protection circuits. These circuits are
designed to protect the rest of the circuitry from damage if a high power signal is inadvertently input
to either of these connectors. If the signal level input to either connector is to high, the signal level
is detected by diode detector and the mechanical relay at the connector is opened. Additionally a
signal is sent to the software via the Multi-Function PCB Assy that alerts the operator that an
overload condition exists.
The SWR Connector can be used to measure SWR and Distance to Fault (DTF) or as a generate
connector providing up to -5 dBm output. When SWR or DTF testing is selected, the signal is
amplified and passes through a 6 dB pad to insure a good match at the SWR Connector. The signal
then goes through two directional couplers and the SWR connector protection relay. The coupler
couples off the forward and reverse power at the SWR Connector. The coupled signals are input to a
dual Log Amp that outputs video signal proportional to the amplitude and phase difference of the
forward and reverse power. From these measurement the software can calculate the SWR of the
UUT. It is necessary to calibrate the SWR circuitry by connecting a short, an open and a 50 Ω
termination to the end of the cable connected to the UUT.
When the 3500 / 3500A is in a Receive Mode, either Transmitter Test or Duplex Test, the signal may
be input to the T/R or ANT.
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