Glenayre Electronics Inc. GL-T8600-CN Manual Do Utilizador
Glenayre Document Number: 9110.00172
DSP Exciter
Issue 1, Rev. I: 01/15/97
THEORY OF OPERATION
Print Date: 02/19/97
Copyright © 1997 Glenayre
Page: 6-15
sec_
6
6.6.2.3
RF Stage Signal Flow
Refer to
. The input to the RF
stage is the second IF signal, supplied by the IF stage circuit through connector pair J10/
P10. The second IF signal carries the paging information on a modulated carrier at the
exciter’s second intermediate frequency. The RF stage converts the second IF signal into
the exciter’s RF output. This RF output carries the same paging information as the second
IF signal, but on a modulated carrier of radio frequency. The RF output is normally applied
to the PA through connector J3. To produce the RF output, the RF stage contains mixer-2,
a filter, and an amplifier. Supporting these circuits are VCO-2 and synth-2. The following
text describes these five circuits and their signal flow.
P10. The second IF signal carries the paging information on a modulated carrier at the
exciter’s second intermediate frequency. The RF stage converts the second IF signal into
the exciter’s RF output. This RF output carries the same paging information as the second
IF signal, but on a modulated carrier of radio frequency. The RF output is normally applied
to the PA through connector J3. To produce the RF output, the RF stage contains mixer-2,
a filter, and an amplifier. Supporting these circuits are VCO-2 and synth-2. The following
text describes these five circuits and their signal flow.
6.6.2.3.1
Mixer-2
Mixer-2 is the second heterodyne mixer. Inputs to mixer-2 are a modulated IF and a carrier.
The modulated IF is the second IF signal. The carrier is supplied by VCO-2. Output from
mixer-2 consists of sum and difference frequencies of the inputs. The sum frequency is
centered near the channel carrier, and the difference frequency about twice the second IF
frequency below that. These two modulated RF carriers are applied to the filter circuit.
The modulated IF is the second IF signal. The carrier is supplied by VCO-2. Output from
mixer-2 consists of sum and difference frequencies of the inputs. The sum frequency is
centered near the channel carrier, and the difference frequency about twice the second IF
frequency below that. These two modulated RF carriers are applied to the filter circuit.
6.6.2.3.2
Filter
The filter is factory-selected and tuned, with a bandwidth determined by carrier frequency
of the transmitter. The inputs to the filter consist of two modulated RF carriers and a key
control.The two carriers are sum and difference frequencies, supplied by mixer-2. The key
control is supplied by the MCU control circuit through J4/P4. The output from the filter,
supplied when the key control is received, is only the sum frequency. This modulated RF,
centered near the channel on-frequency, is supplied to the amplifier.
of the transmitter. The inputs to the filter consist of two modulated RF carriers and a key
control.The two carriers are sum and difference frequencies, supplied by mixer-2. The key
control is supplied by the MCU control circuit through J4/P4. The output from the filter,
supplied when the key control is received, is only the sum frequency. This modulated RF,
centered near the channel on-frequency, is supplied to the amplifier.
6.6.2.3.3
Amplifier
The amplifier provides amplification to the value listed in the specifications as exciter RF
power out. The inputs to the amplifier consist of modulated RF and a key control. The
modulated RF, mixer-2 sum output frequency, is supplied through the filter. Key control is
supplied by the MCU control circuit through J4/P4. Output from the amplifier, supplied
when the key control is received, is an amplified version of the modulated RF. This
amplified output is the exciter RF output.
power out. The inputs to the amplifier consist of modulated RF and a key control. The
modulated RF, mixer-2 sum output frequency, is supplied through the filter. Key control is
supplied by the MCU control circuit through J4/P4. Output from the amplifier, supplied
when the key control is received, is an amplified version of the modulated RF. This
amplified output is the exciter RF output.
6.6.2.3.4
VCO-2
VCO-2 is the RF stage local oscillator. Inputs to VCO-2 are a dc control voltage and an
adjustment. Dc control voltage is supplied by synthesizer-2. The adjustment, which varies
the VCO2 control voltage level, is controlled through the front-panel VCO ADJ access.
This control provides the means for VCO-2 to output a carrier frequency that would
otherwise be beyond the range of the control voltage input. The carrier output, always
second IF frequency below the channel carrier frequency, is applied to mixer-2.
adjustment. Dc control voltage is supplied by synthesizer-2. The adjustment, which varies
the VCO2 control voltage level, is controlled through the front-panel VCO ADJ access.
This control provides the means for VCO-2 to output a carrier frequency that would
otherwise be beyond the range of the control voltage input. The carrier output, always
second IF frequency below the channel carrier frequency, is applied to mixer-2.