Ritron RIT44-465 Manual Do Utilizador
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speaker or transmit voice from a microphone. It is designed to operate at 13.8 VDC to yield 10 Watts
output. The repeater can be set up to repeat all super narrowband signals on the receive frequencies or be
set up via a table to repeat only certain RAN codes. For further explanation see the RITRON programmer
and help file. The unit draws about 140 mA in receive mode and about 3 Amps in transmit mode. This
allows it to be battery operated or battery backed up.
5.1
output. The repeater can be set up to repeat all super narrowband signals on the receive frequencies or be
set up via a table to repeat only certain RAN codes. For further explanation see the RITRON programmer
and help file. The unit draws about 140 mA in receive mode and about 3 Amps in transmit mode. This
allows it to be battery operated or battery backed up.
5.1
DUPLEXER
The duplexer allows for simultaneous transmission and reception of RF signals. There is a receive path and
a transmit path which connect to the RF input and output of the main PCB and a common point at the
antenna connector.
In the receive path is a two-cavity notch filter. This filter allows the receive signal from the antenna
connector to pass through with about 1.5 dB loss, but notches the transmitter RF output signal by 70 dB or
more to prevent overloading the receiver. The transmit path also contains a two-cavity notch filter, this one
tuned to the receive frequency. This filter removes transmitter noise which exists at the receive frequency
and which would interfere with the desired receive signal, if not removed. This filter has about 1.75 dB
loss. Because the notches are very narrow, the duplexer must be re-tuned if the frequency of operation is
changed by more than 50 kHz. If the repeater receive frequency is lower than the transmit frequency then
these two notch filters are physically reversed. The coaxial connectors will cross if this is the case. The low
pass filter, which is physically next to the transmitter connector, will be routed to the receive connector and
the high pass filter, next to the receive connector, will be routed to the transmit connector.
5.2
RECEIVER
5.2.1
Front-End
The receiver front-end comprises the RF amplifier stages with associated filters and the first mixer. The
input signal from the J101 (RX IN) passes through a two resonator bandpass filter formed around L101 and
L102. This filter is narrow enough at 10 MHz to protect the receive RF amplifier, but wide enough to keep
its insertion loss low at 2 dB. This filter stage is followed by the RF amplifier. The RF amplifier stage has
a gain of about 12 dB and a noise figure of 1.5 dB. This stage, along with the first filter, are largely
responsible for the sensitivity of the Repeater. The RF amplifier is followed by a two resonator bandpass
filter formed around L103 and L104. This filter is somewhat narrower than the two-pole filter and thus has
a higher insertion loss at 7 dB. The total filtering action is to limit the number of off-channel interfering
signals that the receiver might be exposed to and to remove signals at the spurious response frequencies of
the mixer which follows. More amplification through Q102 is needed to overcome this second filter section
insertion loss.
The job of the 1
st
mixer, U101 is to convert signals at the receive frequency to that of the 1
st
IF at 43.65
MHz. It does this by mixing the 1
st
local oscillator signal at a frequency 43.65 MHz below that of the
desired receive frequency to the IF frequency of 43.65 MHz. The 43.65 MHz output of U101 exits through
T102 and is routed to the 1
T102 and is routed to the 1
st
IF filter. U101 has a conversion gain of 2 dB and a noise figure of 10 dB.
This performance in combination with the front-end RF amplifier stages determines the sensitivity of the
receiver.
5.2.2
receiver.
5.2.2
1
st
IF
The 1
st
IF stage consists of two two-pole monolithic crystal filters separated by an amplifier. The two
filters are FL101 and FL102. These filters are bandpass in response with a bandwidth of 4 kHz and an
insertion loss of 1.5 dB. To overcome the losses of the filters and to prevent interaction between them, they
are separated by an amplifier formed around Q109.
5.2.3
insertion loss of 1.5 dB. To overcome the losses of the filters and to prevent interaction between them, they
are separated by an amplifier formed around Q109.
5.2.3
2
nd
IF Sub-System