User Manual

Axell Wireless Limited
Technical Literature
FM Rebroadcast Amplifier 55-203201
Document Number 55-203201HBK Issue No. 1 Date 22/12/2008 Page 6 of 23
3. Equipment Overview
FM Rebroadcast Amplifier 55-203201 is built into a wall-mounted, environmentally protected (IP65)
aluminium alloy case; RF ports and connectors are also IP65 standard making the entire enclosure
and connecting ports weatherproof. Handles are provided for carrying the unit and the door is fitted
with locks. A supply isolator switch is fitted inside the unit and there are Power On and Alarm
indicators on the outside of the door.
The amplifier passes one VHF band, 88MHz to 108MHz in the Downlink direction only.
The Downlink signal cable enters the Rebroadcast Amplifier case via the cable gland in the base of
the case (annotated “E” in section 3.4.) and makes a connection to the BNC connector labelled “75
OHMS INPUT” (annotated “B” in section 3.5.). The signal passes through Impedance Matching
Pad 98-000011 which changes the impedance from 75 to 50 and then passes through the
“input” Bandpass Filter 01-004503 which is tuned to pass the Downlink bandwidth of 88MHz to
108MHz and to reject out-of-band noise.
After leaving the filter the signal passes through Low Noise Amplifier 11-008802 and then passes
through Variable Switched Attenuator 10-000701 (annotated “F” in section 3.5.) which can provide
up to 30dB of signal attenuation (in 2dB steps) if required. The attenuator is controlled by the four
toggle switches on the attenuator body; each switch is clearly marked with the attenuation it
provides, and the total attenuation in-line is the sum of the values switched in.
After passing through the attenuator the Downlink signal passes through Low Noise Amplifier 11-
006002 and then into Hybrid Splitter/Coupler 05-000102 which splits the signal into two equal
paths, each path then passes through a 20W Power Amplifier 12-028401 and then the two paths
are recombined by a second Hybrid Splitter/Coupler 05-000102; the resultant signal then passes
through a second Bandpass Filter 01-004503 to further reject out-of-band noise. The signal then
passes through 30dB Directional Coupler 05-000316 which couples off a small portion of the signal
which is passed through an Impedance Matching Pad 98-000011 which changes the impedance
from 50 to 75 and then goes to a BNC monitor/test port for the Downlink output labelled “-30dB
COUPLER” (annotated “P” in 5.3.).
The main RF Downlink path after passing through 30dB Directional Coupler 05-000316 goes to the
N type Port labelled “50 OHMS OUTPUT” (annotated “N” in 5.3.) and the Downlink output cable
which connects to the output port exits the Rebroadcast Amplifier case via the cable gland in the
top of the case (annotated “H” in section 3.4.).