Bird Technologies Group 61470A Benutzerhandbuch

digital processing techniques to provide a wide
range of filter choices to the end user. It is possible
to program digital filters as narrow as 5 KHz and as
wide as 1.5 MHz centered at any frequency within
the licensed range.

The SBIII Digital Signal Booster is capable of oper-
ating as either a Class A booster (no filters greater
than 75 KHz passband width) or as a Class B
booster (having filters with a greater than 75 KHz
passband width). The boosters operating class (A
or B) is user determined via configuration. Class B
operation must be enabled by the customer and
the customer is responsible for registering a
booster operated as Class B with the FCC. System
specifications for the 614 family of signal boosters
are listed in Table 2.

A signal booster has much in common with a
superheterodyne (superhet) receiver. The incom-
ing signal is converted to a lower frequency so that

single channel selectivity can be obtained. It is then
filtered. Unlike the superhet receiver however, the
signal is not demodulated. Instead, it is up-con-
verted back to its original frequency where it is fur-
ther amplified to reach a useful power level.

Figure 1 shows a simplified block diagram that
illustrates the down/up conversion principle. An
incoming signal at (Freq IN) is amplified and
applied to the first mixer along with a signal from a
local oscillator (Freq LO). A third signal at an inter-
mediate frequency (Freq IF) is produced as a result
of the mixing. The intermediate frequency is given
by the following relationship:

The IF signal from the mixer then passes through
digital filtering with single channel bandwidth
before being amplified and passed on to the sec-
ond mixer. The second mixer also receives the
same local oscillator signal (Freq LO). The result is

Frequency Range (MHz)

450 - 470 MHz  ;  470 - 488 MHz

Number of Carriers per Module

Low Density Model

High Density Model

14 uplink and downlink
30 uplink and downlink

Gain

Low Power Version

High Power Version

80 dB (max)
95 dB (max)

Maximum RF Bandwidth

450 - 470 MHz module
470 - 488 MHz module

3 MHz

1.5 MHz

Output Level

Low Power

High Power

22 dBm composite (max)
34 dBm composite (max)

Maximum Continuous Input Level

Operational: -20 dBm

Static w/o damage: -10dBm

RF In/Out Impedance

50 Ohms

Alarms

Form-C Contacts and SNMP v3

Power

90 - 250 VAC, 50/60 Hz

with +24 VDC back-up

Operating Temperature Range

-30°C to +60°C

95% RH (non-condensing)

Table 2: Specifications for the UHF SBIII system.