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ATV Controller for Comtech Modules
This Product will allow the control of Comtech transmit and receiver modules,
it may also control modules from other manufacturers which use the
TSA5055 or SP5055 PLL I/Cs.
Features
· Rotary tuning
· 125KHz channel spacing
· Seven VFOs each for transmit and receive
· Bar graph "S" meter
· PTT with on-board transmit power switching, PA and antenna change over sequencing
· VFO and band scan modes
· 13 or 23cm operation with the same software*
· Linking of transmit and receive VFOs*
· Auto-net function*
· Receive only function*
* By menu selection
A 16 character by 2 line LCD displays transmit and receive frequencies or "S" meter
and menu functions, versions are available with or without backlit displays.
Operation
This unit's functionality can be best appreciated from a description of its operation.
Normally both transmit and receive frequencies are displayed, a ">" symbol in the right
hand column points to a label on the front panel to indicate which function is current.
Receive frequencies and VFO number are display on the top line transmit on bottom,
there are 3 press buttons which function as follows:
VFO
Each press on the VFO button increments the selected VFO, the ">" symbol indicates
which VFO is affected. Note that if linked VFOs is turned on in the menu, both transmit
and receive will advance together. There are seven VFOs each for transmit and receive,
three have special uses; VFO 0 will be overwritten by the band scan function,
VFO 5 holds the lower band scan limit indicated by "SL" and VFO 6 holds the
upper band scan limit indicated by "SU".
Mode
Pressing the MODE button toggles between transmit and receive adjustment mode,
the ">" symbol indicates which is active.
PTT
Pressing the PTT button initiates the transmit sequencing, the order and timing is as follows:
Immediate Energise antenna change over relay
50mS Turn Tx module power on
150ms load synthesiser with transmit frequency
250mS Switch on power amplifier
A second press returns to receive, sequencing as follows:
Immediate PA power is turned off
100mS Tx module power turned off
200mS Antenna change over relay de-energised
Scan Functions
Pressing both VFO and Mode buttons together will start the band scan,
the start frequency is held in Rx VFO 5 and the stop frequency in Rx VFO 6.
Holding both buttons for a couple of seconds will start the VFO scan.
Pressing any button or turning the rotary encoder whilst scanning cancels the function.
"S" meter
Pressing and holding the MODE button for more than 1.5 seconds will set the
"S" meter, this will be displayed on the second line of the LCD display.
Set-up menu
Pressing and holding the VFO button for more than 1.5 seconds will enter the
menu system, changes can be made to each setting with the rotary encoder,
store each setting by pressing the VFO button. The menu can be exit at any time
without storing a change by pressing the MODE button.
Set-up menu functions
"Set IF Frequency" - On receive it's possible the programmed IF offset doesn't
accurately reflect the module's IF frequency, a facility is therefore provided to
adjust the internal IF offset so the displayed frequency matches that being received.
With a weak signal of known frequency tuned so the display indicates the correct
frequency, enter the "Set IF Frequency" mode and use the rotary encoder to adjust
the IF offset for the best picture.
"Set Autonet" - If set to "On" receiver will automatically tune to transmitter output
when the transmitter is powered up. When set to "Off", receive operation isn't affected.
"Set System" - Change to "Receive only" to permanently display the "S" meter,
would normally be used without a transmitter module as all transmit functions are disabled.
"Set Band" - Select either 13cm or 23cm as appropriate, note that when the band is changed
all the VFOs are set to default frequencies.
"Linked VFOs" - If set to on, when changing the selected VFO Rx and Tx VFOs change in unison.
System reset
If the eeprom becomes corrupt normal operation may not be possible, to reset,
hold down the VFO button and cycle power, all internal settings will be restored
to their default values.
Circuit Description
Comtech modules are normally supplied with on board microcontrollers,
these instruct the PLL I/Cs within the "cans" to go to specific frequencies selected via.
DIP switches. The ATV controller talks to the PLL I/Cs directly making the existing
micro redundant, they should be removed from their sockets and kept in case they are
required for de-bugging.
The "brains" of the system are provided by a PIC16F628, this controls the display,
which is used in the 4-bit mode. Data is output from RB4-7 with control from
RB1 (Rs), RB3 (En), and RA1(R/W). The pushbuttons SW2-SW4 are also multiplexed
in to RB4-7, an active low key enable signal is taken from RA7. During display use,
RA7 goes high reverse biasing diodes D1-3 so isolating the switches. The rotary encoder
is input to RB0 and RA5, this function is interrupt driven for smooth operation.
The synthesiser ICs within the Comtech modules are controlled via I2C .
As the receiver "S" meter pin is shared with the I2C address selection pin, independent
device addresses can't be set up, there are therefore separate SDA outputs for
transmit and receive. Diodes D4-6 are incorporated to isolate the modules from the
I2C bus when either module is powered down. The Tx SDA line is not isolated, the
pin level is periodically checked to determine if the transmitter is powered
(for the Auto-net function).
Transmit sequencing is generated from RA3 (PA on), RB2 (antenna relay)
and RA6 (telltale LED and transmit module power). Antenna relay and PA switching
are provided by open collector outputs, these may be used to drive relays directly
(remember to place back EMF protection diodes across the relay coils).
A "confirmation bleep" is provided from RA0 by the filter R16, C3 and R17. This may
be connected to the receiver audio output or alternatively to a piezo sounder by
removing C3 and fitting links in place of R16-17.
The "S" meter is input to RA1, R12 is included to limit current as the port pin is also
used for display R/W.
The power for microcontroller and display is derived from the receivers 5V regulator,
typical power consumption measures 2mA on receive and 10mA in transmit.
This extra load shouldn't cause any problems for the receiver regulator, although
on the 23cm version the regulator will run hot. Power for the LCD back-light is taken
from the 12V supply via resistors R3,4,7,9 and R15 in series, these have been
calculated for an LED current of about 110mA..
Before applying power check that the 5V input (pin 4) is connected to a 5V supply,
excess voltage will destroy the display and microcontroller.
Adjust R18 fully clockwise, with power applied re-adjust for correct display contrast.
Making the connections
Firstly label, then remove the existing microcontrollers from receiver and transmitter PCBs,
keep safe in case they are required later. Follow table 1 for interconnections to
transmit and receive PCBs, extracts from the manufacturers data sheet have been
reproduced to help with identification.
The controller has I2C "pull-up" resistors incorporated, if leaded resistors are fitted under
the receiver or transmitter PCBs they may be left in place but are not required. Depending
on the source, some modules will have one or
perhaps two resistors
Controller connections
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Control ler Pin Number
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Name
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Function / Connection
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1
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Tx Power
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Output from transmit power switch, connect to transmitter module power input (centre pin of DC socket on power module). Power is then supplied by the controller NOT by the transmitter power socket, this is required for the Autonet mode to operate correctly.
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2
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12V Supply
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12 V supply for back-light and transmit power. Connect to the system 12V supply, this would normally be the centre pin of receiver DC supply socket.
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3
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Gnd
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System ground. Connect to receiver screening can. If a transmitter module is used a ground connection should be made between transmit and receiver screening cans.
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4
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5V Supply
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Micro and display 5V supply. Take this from the receiver 5V regulator output, this can be found on the 3rd pin from antennae socket end on the receiver module, see diagram.
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5
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Antenna relay
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Open collector output that can be used to switch an antenna relay, this output is sequenced with Tx OK and Tx Power. Transistor turns on in transmit so pulling pin low, in receive this output is open circuit.
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6
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Tx OK
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Open collector output which can be used to switch a power amplifier on (possibly via a relay), this output is sequenced with Antenna relay and Tx Power. Transistor turns on in transmit so pulling pin low.
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7
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"S" Meter
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"S" meter input to the micro. Connect to "S" meter output of tuner, which is the 6th pin along counting from the antenna end of the tuner, can. Note that a link must be made within the tuner for the "S" meter to function, this can be found under the screening can at the point that pin 6 enters.
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8
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Key press confirmati on Beep
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Produces a "beep" output when keys are pressed. May be directly connected to audio output of receiver module or alternatively connected to a piezo sounder. If using a sounder omit C3 and fit links in place of R16 and R17.
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9
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Tx SCL
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Transmit serial clock output. Connect to SCL pin of transmit module, this is the 5th pin from antenna end.
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10
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Tx SDA
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Transmit serial data pin. Connect to the transmitter SDA pin, 6th pin from transmitter module antenna connection.
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11
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Rx SCL
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Receiver serial clock output pin, connect to the SCL pin on receiver module. This is the 12th (last) pin from antenna end.
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12
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Rx SDA
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Receiver serial data pin, connect to the SDA pin on receiver module. This is the 11th pin from antenna end.
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Specifications
Voltage and current ratings
Logic (display and microcontroller) 5V at 2mA rx and 10mA Tx (typical)
Display back-light and Tx switch 12V at 110mA for display + Transmit module current
Transmitter module power switch Maximum output current 500mA
TxOK and Antenna relay drive Maximum current 500mA, relay voltage 28V
Ensure a back EMF diode is fitted across the relay coil
Tuning specification
23cm Transmit 1240 - 1320MHz
23cm Receive 800 - 1800MHz
13cm Transmit 2310 - 2450MHz
13cm Receive 2200 - 2700MHz
IF offset 479.5MHz (Oscillator high for 23cm and low for 13cm)
IF offset adjustment range 474.5 - 484.5MHz
Channel spacing 125KHz
Steps per revolution 24
Tuning rate 125KHz - 10.125MHz per step depending on speed of rotation
Document history
27-11-03
Modified from published article incorporating changes to PCB and firmware.
PCB and firmware currently V3.0.
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