User's Manual

P. G. TM0047
2-1
SECTION 2. THEORY OF OPERATION
2.0 GENERAL
As explained in Section 1, the A300 is a bidirectional amplifier, which provides 20 dB of
gain in both the SMR and PCS wireless transmit and receive bands. The block diagram
of the amplifier is shown in Figure 2-1.
2.1 DESCRIPTION
2.1.1 - The unit is composed of two diplexers, two independent bidirectional amplifiers
and alarm and voltage regulation circuits.
2.1.2 - The diplexers U1 and U2 divide power between the SMR and PCS bidirectional
amplifiers. In each bidirectional amplifier additional bandpass diplexers separate signals
for the uplink and downlink amplifiers.
2.1.3 - The bias condition of devices in the amplifiers is monitored. If the bias changes
outside certain limits a fault condition is indicated. The downlink RF output power in
each band is also monitored. If the power in either band drops below established limits
a FAULT condition is indicated.
When a FAULT condition occurs the unit transmits the unit identification (or "Fault
Code") by two level amplitude modulation of a low frequency carrier placed on the cable
center conductor. The signal is transmitted as a short burst repeated at approximately
80 second intervals while the fault condition persists. The fault code can be
reprogrammed as described in Section 3.2. While a NORMAL condition exists the
amplifier transmits an OK code at intervals of approximately 80 minutes.
2.1.4 - The voltage regulators take 24 - 28 VDC input and provide 20 VDC and 12 VDC
outputs. A zener diode provides transient protection against voltage spikes on the cable.
2.1.5 - The A300 dual band bidirectional amplifier requires external DC power to be
supplied through the 5-pin DIN receptacle. The unit should be powered locally by the
PS293 external power source. The local power source is isolated from J1 and J2.
The unit provides DC continuity from J1 to J2 to allow downstream cable powered
amplifiers to receive their power from upstream power sources such as the PS212 and
PS213. In addition, status signals from downstream cable powered amplifiers are
passed through the amplifier from J1 to J2.