SC5313A Operating & Programming Manual
Rev 1.0.2
10
The RF attenuators provide attenuation when required. RF ATTEN#1 attenuation should be stepped up
as the signal power at the RF port increases above -10 dBm. Nonlinear components of the signal such as
IMD3 and second order harmonics will increase in magnitude as the input signal increases, therefore the
user should exercise good judgment to determine when to use RF ATTEN#1. Do not over attenuate
because this will hurt the signal to noise ratio.
RF ATTEN#2 is used when if the input signal needs further suppression to improve linearity. It should
also be used if RF AMP#1 is enabled to improve sensitivity, but as a result the level at the input of RF
AMP#3 (always in the path) may be too high. Step up the attenuation of RF ATTEN#2 to ensure the
system (resulting from RF AMP#3) is not driven too hard. Finally RF ATTEN#3 is used to control the level
to the IQ demodulator when RF AMP#2 is enabled (switched into the signal path).
There is also an auxiliary RF input to the device. This input is almost identical to the main RF input with
the exception of having an extra switch path. The intended use of this port is to allow the user a
calibration path without having to detach the device under test (DUT) that is already attached to the
main RF input port. The user must perform in-situ equalization to remove IQ errors such as phase
imbalance and quadrature gain offsets that are inherent to the device.
There are nine low pass filters in the RF filter bank. These filters are automatically selected when the
user enters the operating frequency. These filters can also be selected manually should the user choose
to do so. As with all filters there is generally an amplitude roll-off as the frequency nears its 3 dB cutoff
point so it is important to understand that frequencies near to the cutoff point may experience a slightly
faster roll-off of its IF bandwidth. A typical 1 dB IF bandwidth (IQ) is about 160 MHz. The user may want
to choose a higher frequency filter if this becomes a problem. See the programming section in this
manual for more details. The filters in both the RF and LO filter banks are identical and are listed below.
Filter Number
1 dB Cutoff Frequency
0
400 MHz
1
500 MHz
2
650 MHz
3
1000 MHz
4
1400 MHz
5
2000 MHz
6
2825 MHz
7
3800 MHz
8
6000 MHz
LO Input Section
The SC5313A requires an external RF signal as its “Local Oscillator” (LO) for the frequency conversion
process. The external RF signal must be connected to the “LO in” port. The typical required input level is
-3 dBm to 3 dBm. These levels are required to sufficiently drive the IQ demodulator for good linearity
performance and conversion loss. The LO signal is conditioned through a bank of low-pass filters to
reduce the signal harmonics. Reducing the harmonics produces a “purer” signal tone, improving the
