Futurecom DVRS, Руководство пользователя

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8A083X30 Rev.11
APX Series P25 Interface
DVRS
User’s Guide
January 2019 Page 18 of 94
In-Band
The in-band DVRS models are equipped with two sets of filters, which are required in
order to ensure interference-free operation when both the MSU and DVR are
transmitting and receiving simultaneously in the same frequency band. The DVR is a full
duplex capable repeater, equipped with a duplexer, which provides sufficient isolation to
prevent desense during DVR repeat activation. The DVR duplexer also provides 40 dB
isolation on the Mobile radio transmit / receive frequencies. The filters installed at the
output of the MSU are designed to provide 40 dB isolation on the DVR transmit and
receive frequencies.
IMPORTANT!
The above filtering isolation must be complemented by 30dB minimum antenna
isolation (between the DVR and Mobile Radio antennas) in order to ensure
interference-free operation. It is recommended that the Mobile antenna is mounted
on the roof of the vehicle while the DVR antenna is mounted on the trunk.
Each DVRS is equipped with custom filters tuned to the specified frequency
bands
– note the frequency range specified on the filter Labels.
Programming the DVR / Mobile radio to operate on frequencies outside of the
original specified bands may result in intermittent or complete loss of
communications. Frequency changes may require filter retuning or replacement.
The in-band DVRS models are also equipped with an RF bypass switch, which
bypasses the filtering at the output of the MSU when a “DVR – Disabled” TG is selected
on the MSU control head (see
Figure 5 ).
When a “DVR – Enabled” TG is selected on the MSU CH, the RF switch automatically
connects the extra filters between the MSU antenna port and the MSU antenna to
ensure interference-free operation.
The complex in-band filtering is only feasible if sufficient frequency gap is present
between the DVR frequencies
and the MSU frequencies associated with the “DVR -
Enabled” TGs.
For more information on the feasible filtering options, please refer to the DVRS Ordering
Guides.
As an option, an in-band DVRS can also be configured as simplex only (
Figure 6 ). The
simplex in-band configuration however still requires DVR and in-band filters.
NOTE:
The DVR and MSU always require two (or three in the case of dual band MSU) separate
antennas.
NOTE:
The In-Band filters connected to the MSU have typical insertion loss of 1.5dB.