Simoco EMEA Ltd SB2K5354O2O2V Manual De Usuario
SGD-SB2025NT-TUM, Part 1
Jan 12
Page 34
TECHNICAL DESCRIPTION
The Micro Controller sends programming data to the synthesiser ICs on the Rx and Exciter
modules each time the channel is changed as well as on PTT. This information is communicated
to the Rx and Exciter modules by way of bussed data and clock lines on SKC/D-18 and SKC/D-15
(Exciter/Rx) and an individual module strobe on SKC/D-17. A lock detect signal from each module
on SKC/D-16 is read by the Micro Controller.
modules each time the channel is changed as well as on PTT. This information is communicated
to the Rx and Exciter modules by way of bussed data and clock lines on SKC/D-18 and SKC/D-15
(Exciter/Rx) and an individual module strobe on SKC/D-17. A lock detect signal from each module
on SKC/D-16 is read by the Micro Controller.
In addition to the synthesiser programming bus, an I
2
C bus goes to each of the modules. This bus
is currently unused.
5.4.2
Tx Signal Processing
Tx audio may be sourced from a number of different paths. These include VF from line, T/T audio,
the microphone, and DC FM/Wideband input, Tone generator from the Micro Controller, Test Tx
VF inject from the Monitor port, CTCSS generator and the internal RF modem.
the microphone, and DC FM/Wideband input, Tone generator from the Micro Controller, Test Tx
VF inject from the Monitor port, CTCSS generator and the internal RF modem.
The Tx VF path is readily user configurable with most major functional blocks being possible to
either select or bypass by means of links (refer to Table 4 – Micro Controller Jumpers for details
of link settings). The VF from line enters the board on SKH-14 and RV4 (Tx VF gain) provides gain
adjustment to accommodate different line levels. This is followed by a selectable compressor
(IC34A) with 30 dB dynamic range. The output of the compressor, apart from being fed to the
main Tx audio path, is also connected to the input side of the “Line” Fast Frequency Shift Keying
(FFSK) modem and via a gain control pot the speaker amplifier (IC60). Following the main Tx
audio path, IC36B serves to switch the VF further on the Tx audio path or, under the control of the
external input on SKH-13, to loop it back to the line output via RV7, which provides level
adjustment for the looped back signal. From this switch, the VF passes though a second switch
IC32B under the control of the Micro Controller and the external Tx talk line on SKH-10. This
switch is used to disable the line Tx VF path. From here the VF passes through a pre-emphasis
stage C66, R67 and a 300 Hz high pass filter (IC30B and IC29A) each of which is selectable
through links. The output of this filter is fed to IC30A a summer/limiter amplifier.
either select or bypass by means of links (refer to Table 4 – Micro Controller Jumpers for details
of link settings). The VF from line enters the board on SKH-14 and RV4 (Tx VF gain) provides gain
adjustment to accommodate different line levels. This is followed by a selectable compressor
(IC34A) with 30 dB dynamic range. The output of the compressor, apart from being fed to the
main Tx audio path, is also connected to the input side of the “Line” Fast Frequency Shift Keying
(FFSK) modem and via a gain control pot the speaker amplifier (IC60). Following the main Tx
audio path, IC36B serves to switch the VF further on the Tx audio path or, under the control of the
external input on SKH-13, to loop it back to the line output via RV7, which provides level
adjustment for the looped back signal. From this switch, the VF passes though a second switch
IC32B under the control of the Micro Controller and the external Tx talk line on SKH-10. This
switch is used to disable the line Tx VF path. From here the VF passes through a pre-emphasis
stage C66, R67 and a 300 Hz high pass filter (IC30B and IC29A) each of which is selectable
through links. The output of this filter is fed to IC30A a summer/limiter amplifier.
The summing point of this amplifier also serves to combine the audio from the T/T path, which is
level adjusted by RV3, the microphone which is processed through a similar compression, pre-
emphasis and filtering chain as the line VF, the tone (Morse code) signal from the microprocessor,
the DC FM input, which enters the board on SKH-6 and the Test Tx VF injection from SKE-2. The
latter three inputs are all at fixed levels. RV2 on IC30A provides overall gain adjustment.
Following the limiter amplifier is the Tx VF low pass filter. The standard Bessel filter has a 3.4 kHz
cut off frequency. A second summing amplifier IC24B follows, which combines the CTCSS,
optional modem (IC52 and IC54) and Wideband audio inputs with the Tx VF. Level adjustment of
the CTCSS signal is in three 0.85 dB steps either above or below the nominal level (10% of max
dev). These level steps are setup using the Configure screen of MxTools. The output of this final
stage is fed to two microprocessor-controlled digipots, which serve to adjust the modulating signal
level to the VCO and the reference oscillator. A third digipot is used to provide an offset null for the
reference oscillator centre frequency. Adjustment of these levels is also by way of MxTools using
the Channel Edit screen.
level adjusted by RV3, the microphone which is processed through a similar compression, pre-
emphasis and filtering chain as the line VF, the tone (Morse code) signal from the microprocessor,
the DC FM input, which enters the board on SKH-6 and the Test Tx VF injection from SKE-2. The
latter three inputs are all at fixed levels. RV2 on IC30A provides overall gain adjustment.
Following the limiter amplifier is the Tx VF low pass filter. The standard Bessel filter has a 3.4 kHz
cut off frequency. A second summing amplifier IC24B follows, which combines the CTCSS,
optional modem (IC52 and IC54) and Wideband audio inputs with the Tx VF. Level adjustment of
the CTCSS signal is in three 0.85 dB steps either above or below the nominal level (10% of max
dev). These level steps are setup using the Configure screen of MxTools. The output of this final
stage is fed to two microprocessor-controlled digipots, which serve to adjust the modulating signal
level to the VCO and the reference oscillator. A third digipot is used to provide an offset null for the
reference oscillator centre frequency. Adjustment of these levels is also by way of MxTools using
the Channel Edit screen.
5.4.3
Rx Signal Processing
In a similar fashion to the Tx audio path, the major functional elements of the Rx audio path are
capable of being selected or bypassed by means of links.
capable of being selected or bypassed by means of links.
Discriminator audio enters the board on SKD-3 and is fed to a selectable 300 Hz high pass filter
comprising IC37 and IC38B. This output or an unfiltered version of the discriminator audio is fed
via a switch IC32A to the TTR (repeater) path. The switch is used to disable talk through audio
under the control of the microprocessor and the external Tx talk line on SKH-10. Following the
high pass filter, a selectable 3.4 kHz cut-off low pass filter IC38A and IC39B connects to the de-
emphasis circuit IC39A. From here the audio passes through the mute switch IC32C that is under
control of the microprocessor and on to the Rx talk switch IC36C, which is controlled externally
from SKH-3. This second switch is used to disable Rx audio to line. A final switch IC36A selects
comprising IC37 and IC38B. This output or an unfiltered version of the discriminator audio is fed
via a switch IC32A to the TTR (repeater) path. The switch is used to disable talk through audio
under the control of the microprocessor and the external Tx talk line on SKH-10. Following the
high pass filter, a selectable 3.4 kHz cut-off low pass filter IC38A and IC39B connects to the de-
emphasis circuit IC39A. From here the audio passes through the mute switch IC32C that is under
control of the microprocessor and on to the Rx talk switch IC36C, which is controlled externally
from SKH-3. This second switch is used to disable Rx audio to line. A final switch IC36A selects