User Manual

Axell Wireless Limited
Technical Literature
L.A. M.T.A. Remote Sites
Document Number 80-301401HBKM Issue No. 1 Date 13/06/2008 Page 24 of 148
3.4. VHF/UHF BDA Unit (80-301403)
VHF/UHF BDA Unit (80-301403) provides the amplification stages for the VHF and UHF Lowband
paths, The unit is housed in a wall mount case 600x600x250mm (24” x 24” x 10” approx).
The Downlink VHF signal is received at the port labelled “VHF D/L INPUT” (Annotated A in the picture
in section 3.4.4.2.). The Downlink VHF path passes through a bandpass filter to remove out of band
noise and then a switched attenuator providing 0 to 30 dB of RF signal attenuation.
After leaving the attenuator the VHF Downlink signal passes through a 5W amplification stage, this
amplification stage is straddled by an Automatic Gain Control assembly providing limiting to the output
signals in the case of high input signals.
After leaving the Amplification/AGC stage the VHF Downlink signal passes through a second
bandpass filter and exits the BDA via the port labelled “VHF D/L OUTPUT” ( B in section 3.4.4.2.).
The Uplink VHF Signal is received at the port labelled “VHF U/L INPUT” (C in section 3.4.4.2.). The
VHF Uplink path passes through a bandpass filter to remove out of band noise and then a switched
attenuator providing 0 to 30 dB of RF signal attenuation.
After leaving the attenuator the VHF Uplink signal passes through a 5W amplification stage, this
amplification stage is straddled by an Automatic Gain Control assembly providing limiting to the output
signals in the case of high input signals.
After leaving the Amplification/AGC stage the VHF Uplink signal passes through a second bandpass
filter and exits the BDA via the port labelled “VHF U/L OUTPUT” (D in section 3.4.4.2.).
The Downlink UHF Lowband signal is received at the port labelled “UHF LOW D/L INPUT” (E in
section 3.4.4.2.). The signal passes through a switched attenuator providing 0 to 30 dB of RF signal
attenuation and then into the amplification stage. The Downlink UHF Lowband amplification stage is
provided by tow amplifier modules, the first is a 15dB gain Low Power Amplifier and the second is a
20W, 23dB gain power amplifier. Both amplification stages are straddled by an Automatic Gain
Control assembly providing limiting to the output signals in the case of high input signals.
The input to the AGC detector is provided by the output of a 30dB tap. After leaving the
Amplification/AGC stage the Downlink UHF Lowband signal exits the BDA via the port labelled “UHF
LOW D/L OUTPUT” (F in section 3.4.4.2.).
The Uplink UHF Lowband signal is received at the port labelled “UHF LOW U/L INPUT” (G in section
3.4.4.2.). The signal passes into a Low Noise Amplifier providing 15dB of gain and then into a
switched attenuator providing 0 to 30 dB of RF signal attenuation. After the attenuator the Uplink UHF
Lowband signal passes into a second stage of amplification provided by a 5W, 30dB gain Power
Amplifier, this amplification stage is straddled by an Automatic Gain Control assembly providing
limiting to the output signals in the case of high input signals.
The Uplink UHF Lowband signal exits the BDA via the port labelled “UHF LOW U/L OUTPUT” (H in
section 3.4.4.2.).
VHF/UHF BDA Unit (80-301403) is provided with a 24V DC input to power the amplifier modules
within and those amplifier modules are configured to provide alarm status reports. Separate alarm
contact outputs are provided for the VHF and the UHF Lowband paths.