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R & S E K 8 9 5 / R & S E K 8 9 6
User Manual
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Preselection R&S FK 890H1 (Option)
1.3.10 Preselection R&S FK 890H1 (Option)
1.3.10.1 Design
Preselection R&S FK!890H1 consists of a printed
circuit board, a screen set, two RF covers, two
black extracting levers, the interface to the
carrier board and of HF interfaces.
Preselection R&S FK 890H1 is connected to the
rear panel via the HF interfaces and a cable
from the cable set and to the IF / AF processor
via cable W13.
1.3.10.2 Functioning
(See Fig. 1.14)
Depending on the receive frequency (f
Rx
)
selected by the operator, the antenna signal is
routed to the HF unit either via the lowpass
filter (10 to 500 kHz) or via the bandpass filter
(0.5 to 1.5 MHz) or via one of the eight
suboctave filters.
The suboctave filters cover the following
frequency ranges:
f 1.500 to 2.181 MHz
f 2.181 to 3.172 MHz
f 3.172 to 4.613 MHz
f 4.613 to 6.708 MHz
f 6.708 to 9.755 MHz
f 9.755 to 14.186 MHz
f 14.186 to 20.630 MHz
f 20.630 to 30.000 MHz
By means of the suboctave filters, signals in the
short>wave range (1.5 to 30 MHz) with an
f interfering frequency f
inter
= f
1
> f
2
are
further attenuated by more than 20 dB and
signals with an
f interfering frequency f
inter
= f
1
+ f
2
are
attenuated by more than 40 dB.
If the frequency of the interfering signal is in>
side the stopband of the lowpass or bandpass
filter, the interfering signal is attenuated in the
VLF range (10 kHz to 1.5 MHz) in the same way
as in the short>wave range.
In the stopbands of the filters interference
caused by cross modulation and distortion
products of the third order (f
inter
= 2¥f
1
±f
2
)
decreases with the second / third exponent of
the selection value.
By use of the preselection the oscillator inter>
fering voltage at the antenna input is reduced
and the attenuation for the first image fre>
quency (f
image
=f
Rx
+ 2¥f
1st!IF
with f
1st!IF
=
41.44 MHz) improved by more than 20 dB.
A limiting circuit at the output of Preselection
R&S FK 890H1 protects the receiver input.
By use of the preselection the permissible input
voltage at the antenna input is increased to
30!V
EMF
.
6164.0717.02_01
> 1.26 >
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