SC5305A Operating & Programming Manual
50
Spectral Specifications
RF input range
(1)
................................................................................................................................. 1 MHz to 3.9 GHz
IF output center frequency
............................................................................................................................... 70 MHz
IF output polarity
(2)
............................................................................................................... Non-inverted/Inverted
IF bandwidth (3 dB)
Final IF filter bypassed ................................................................................................................................ > 20 MHz
Final IF filter enabled (default) ................................................................................................................ > 18 MHz
Figure 5. Typical output IF response of filter options. A maximum of two IF filter options are available. Standard
IF option is a 20 MHz bandwidth path and a bypass (no filter) path.
-80
-70
-60
-50
-40
-30
-20
-10
0
40
50
60
70
80
90
100
A
m
p
lif
u
d
e
(d
B
c)
IF frequency (MHz)
10MHz
18 MHz
40 MHz
(1)
RF input below 1 MHz suffers from amplitude roll-off and calibration is not valid below this
lower-end frequency. In the frequency range below the specified IF bandwidth (< ~15 MHz)
the first LO leakage appears inside the IF band. This LO leakage will appear as ~DC when the
RF is converted to baseband in the final analysis. Furthermore, because the LO appears inside
the IF band it will inter-modulate with the input RF signal to produce higher order in-band
spurious signals that may degrade signal integrity. It is recommended to attenuate the RF
signal before the first mixer by applying RF attenuation or attenuate after the first mixer by
applying IF1 attenuation. Suppressing the RF amplitude in front of the downconversion path
will reduce the spurious signal levels.
(2)
The IF output polarity refers to the conversion polarity of the downconverter. When the
polarity is inverted the spectral content of at the output is inverted with respect to the input;
this process is commonly known as “spectral inversion” or “spectral flipping”. The choice
depends on the application. For digitizers that are sampling the IF in the even order Nyquist
zones that naturally inverting spectra, having the IF polarity inverted will produce non-
inverted baseband, and vice-versa. However this is only a convenience in this application case
because inverted spectrum, once digitized, can easily be re-inverted mathematically.