8M083X25 R14
APX Series P25 Interface
DVRS Installation & Programming Guide
–
PART I
January 2019
Page 26 of 153
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 filter 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 MSU in-band antenna is
mounted on the roof top of the vehicle while the DVR antenna is mounted on the
trunk. Each DVRS is shipped equipped with custom filters tuned to the specified
frequency bands
– note the frequency range specified on the filter labels.
Programming the DVR / MSU 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” mode is selected on the MSU CH, the RF Switch 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 require two or three (in the case of dual band MSU) separate
antennas.
IMPORTANT!
In all In-Band DVRS configurations, the MSU Transmit power must not exceed 50
Watts on DVRS Enabled MSU Modes due to the in-band filters power rating.
The in-band filters connected to the MSU have typical insertion loss of 1.5dB.
