V L F - H F R E C E I V E R S R & S E K 8 9 5 / R & S E K 8 9 6
User Manual Digitally Tuned RF Selector R&S FK 896D (Option)
6164.0171.02_01
- 1.32 -
1.3.15.1 Design
The optional Digitally Tuned RF Selector
R&SFK896D consists of two printed circuit
boards, namely the actual Digital Selection
R&S FK 2020 (R&S FK 896D, mod.02) or Digital
Selection R&S FK 2040 (R&S FK 896D, mod.04),
an interface module as well as an adapter (part of
interface module). It contains three interface
connectors which are used for HFsignal input and
output as well as for connection to the SERBUS.
1.3.15.2 Functioning
(See Fig. 1.19)
The Digitally Tuned RF Selector R&S FK 896D is
used in VLF-HF Receiver R&S EK 896, where it is
switched into the receive path between the HF
amplifier and the HF unit. At a spacing of 10 %
from the nominal frequency, the digitally tuned RF
selector ensures a selectivity of > 20 dB
(R&S FK 2020) or > 40 dB (R&S FK 2040).
The receive signal is routed from HF socket X41
(RXIN) to the overload circuit. The latter ensures
that the HF signal path is interrupted at input
currents of > 4 A and input voltages of >
10 V EMF.
Further the receive signal is routed via a 50-MHz
lowpass filter (suppression of VHF and UHF
frequencies) to the contacts of two relays. In
bypass operation the filters of the digitally tuned
RF selector are bypassed by these relays.
The only exception is the 50-MHz lowpass filter in
which case the receive signal is directly routed to
HF output X45 (RXOUT) via the relay contacts.
If selection is switched on, the receive signal is
controlled by the 1.5-MHz signal. At receive
frequencies in the range from 0 to 1.5 MHz, the HF
signal is routed to a 1.5-MHz lowpass filter and
further to HF output X45 (RXOUT). At receive
frequencies in the range from 1.5 to 30 MHz, the
receive signal is routed via avariable single-circuit
filter to an amplifier or an attenuator depending on
signal GAINCONTROL. The latter guarantees, at
switched-on selection, a gain of 0 to +2 dB from
X41 (RXIN) to X45 (RXOUT). From the amplifier,
the signal SELOUT is routed to HF output X45
(RXOUT) via relay contacts.
Depending on its use, the digital selection can
either be controlled via the SERBUS or else via
discrete lines. The following functions are
ensured:
• Exchange of control, data, acknowledgeand
monitoring signals with the processorof the
Receiver R&S EK 896
• Switchover of filter assemblies in accordance
with the set operating frequency
• Bypass / selection operation switchover
• Interruption of receive signal path in thecase
of overcurrent or overvoltage
• Switchover between amplifier and attenuator
1.3.15 Digitally Tunded RF Selector R&S FK 896D (Option)
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