Bird Technologies Group 5PI613805 Manual De Usuario
TXRX Systems Inc. Manual 7-9408-1.2 07/25/05 Page 7
61-38-05 UserMan page 7 of 38
INTRODUCTION
This publication, Instruction Manual 7-9408-1, con-
tains information to support the installation, opera-
tion, and maintenance of the model 61-38-05
signal booster system. Also included in this manual
are the procedures necessary for field adjust-
ments. It is assumed that procedures in this man-
ual will be carried out by a skilled electronics
technician who is familiar with the communications
system. This manual also gives an elementary
explanation of the operation of signal boosters and
signal distribution systems. For a more detailed
discussion of signal booster systems and design
methods, refer to the TX RX Systems Inc. publica-
tion "SEMINAR SUBJECTS" entitled "Repeater
Amplifier Systems: Principles and Applications" (lit-
erature number C2012J94). Contact your TX RX
Systems, sales representative if you wish to order
a copy.
tains information to support the installation, opera-
tion, and maintenance of the model 61-38-05
signal booster system. Also included in this manual
are the procedures necessary for field adjust-
ments. It is assumed that procedures in this man-
ual will be carried out by a skilled electronics
technician who is familiar with the communications
system. This manual also gives an elementary
explanation of the operation of signal boosters and
signal distribution systems. For a more detailed
discussion of signal booster systems and design
methods, refer to the TX RX Systems Inc. publica-
tion "SEMINAR SUBJECTS" entitled "Repeater
Amplifier Systems: Principles and Applications" (lit-
erature number C2012J94). Contact your TX RX
Systems, sales representative if you wish to order
a copy.
The 61-38-05 booster family is designed to cover
the frequency range of 138 to 174 MHz in two non
contiguous bands, One version covers 138 to 144
MHz for operation in Canada and another version
to cover 148 to 174 MHz. This version is also used
to cover U.S. land-mobile frequencies from 150.8
to 174 MHz. Units for both bands share common
active circuitry but differ in the passive filter units
that duplex the downlink and uplink branches from
a common input or to a common output.
the frequency range of 138 to 174 MHz in two non
contiguous bands, One version covers 138 to 144
MHz for operation in Canada and another version
to cover 148 to 174 MHz. This version is also used
to cover U.S. land-mobile frequencies from 150.8
to 174 MHz. Units for both bands share common
active circuitry but differ in the passive filter units
that duplex the downlink and uplink branches from
a common input or to a common output.
Because
signal booster systems are often times subjected
to very demanding environments with extreme con-
ditions of temperature, moisture, dirt and corro-
sives, the system is housed in a high quality
(NEMA style) enclosure. This type of housing
maintains its dimensional stability and appearance
better than other materials. Figure 1 shows a front
view of the unit with the door opened.
to very demanding environments with extreme con-
ditions of temperature, moisture, dirt and corro-
sives, the system is housed in a high quality
(NEMA style) enclosure. This type of housing
maintains its dimensional stability and appearance
better than other materials. Figure 1 shows a front
view of the unit with the door opened.
The system uses linear RF active amplifiers, filters,
OLC (output level control) circuitry, and DC power
sources to adequately boost the level of the RF sig-
nals. Linear power amplifiers (Class-A) are used in
the amplifier stages of this signal booster system in
contrast to the highly efficient Class-C power
amplifiers used in the output stages of most FM
landmobile transmitters. Linear amplifiers are
biased for a relatively high continuous DC current
drain that does not change with changing RF drive
levels.
OLC (output level control) circuitry, and DC power
sources to adequately boost the level of the RF sig-
nals. Linear power amplifiers (Class-A) are used in
the amplifier stages of this signal booster system in
contrast to the highly efficient Class-C power
amplifiers used in the output stages of most FM
landmobile transmitters. Linear amplifiers are
biased for a relatively high continuous DC current
drain that does not change with changing RF drive
levels.
Class-A amplifiers generally have the lowest effi-
ciency of the various amplifier types, typically in the
range of 25-33%. They also draw relatively high
ciency of the various amplifier types, typically in the
range of 25-33%. They also draw relatively high
current levels on a continuous basis, making heat
dissipation an impor tant factor. Their biggest
advantage is faithful reproduction of the input
waveform which results in the lowest levels of inter-
modulation distor tion products (IM) of all the
classes of amplifiers. IM generation is a serious
design consideration when two or more channels
are simultaneously present in the same amplifier
stage.
dissipation an impor tant factor. Their biggest
advantage is faithful reproduction of the input
waveform which results in the lowest levels of inter-
modulation distor tion products (IM) of all the
classes of amplifiers. IM generation is a serious
design consideration when two or more channels
are simultaneously present in the same amplifier
stage.
Preselector filters are used in the system to provide
a number of functions including; reduction of the
level of undesired signals that may enter the sys-
tem and also help suppress any IM products that
may be inadvertently generated. They also pro-
duce a convenient impedance characteristic that
allows multiple branch paths to be tied together to
a common input/output port. This is accomplished
using critical length cables from the filter assem-
blies to a tee junction.
a number of functions including; reduction of the
level of undesired signals that may enter the sys-
tem and also help suppress any IM products that
may be inadvertently generated. They also pro-
duce a convenient impedance characteristic that
allows multiple branch paths to be tied together to
a common input/output port. This is accomplished
using critical length cables from the filter assem-
blies to a tee junction.
The output level of any signal passing through a
signal booster is determined by the input signal
level, the gain of the booster, and the maximum
output power per carrier rating of the booster. The
high power output stages used in the signal
booster may be damaged by excessive input sig-
nals. An output level control (OLC) circuit is added
to each amplifier chain to protect the amplifiers and
reduce spur ious signals. The OLC circuit is
designed to maintain the maximum output level of
the booster during times of excessive input signal
levels.
signal booster is determined by the input signal
level, the gain of the booster, and the maximum
output power per carrier rating of the booster. The
high power output stages used in the signal
booster may be damaged by excessive input sig-
nals. An output level control (OLC) circuit is added
to each amplifier chain to protect the amplifiers and
reduce spur ious signals. The OLC circuit is
designed to maintain the maximum output level of
the booster during times of excessive input signal
levels.
OLC circuitry actuates when a predetermined max-
imum output level is reached. The output power
level in all OLC branches is sampled, and then fed
to a detector circuit which generates a DC voltage
proportional to the output power level. The DC out-
put of the detector is then applied to a control cir-
cuit which develops a voltage used to control a
variable electronic attenuator. The electronically
controlled attenuator is placed within the amplifier
signal path and reduces the incoming signal by an
amount necessary to keep the power from exceed-
ing the maximum safe level. The gain reduction
range is typically from 5 to 40 dB which is more
than adequate for most real life situations.
imum output level is reached. The output power
level in all OLC branches is sampled, and then fed
to a detector circuit which generates a DC voltage
proportional to the output power level. The DC out-
put of the detector is then applied to a control cir-
cuit which develops a voltage used to control a
variable electronic attenuator. The electronically
controlled attenuator is placed within the amplifier
signal path and reduces the incoming signal by an
amount necessary to keep the power from exceed-
ing the maximum safe level. The gain reduction
range is typically from 5 to 40 dB which is more
than adequate for most real life situations.
OLC circuitry should not be considered a panacea
for a poor system design. One undesirable affect of
OLC is that the signal level of all signals being pro-
cessed by the branch will be reduced when the cir-
c u i t r y i s a c t i v a t e d . T h i s m e a n s t h a t t h e
for a poor system design. One undesirable affect of
OLC is that the signal level of all signals being pro-
cessed by the branch will be reduced when the cir-
c u i t r y i s a c t i v a t e d . T h i s m e a n s t h a t t h e