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DDS VFO 2 Construction Manual – Issue 1

Page 1

DDS

VFO

2

C

ONSTRUCTION

M

ANUAL

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2
3
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Содержание DDS VFO 2

Страница 1: ...DDS VFO 2 Construction Manual Issue 1 Page 1 DDS VFO 2 CONSTRUCTION MANUAL ...

Страница 2: ...ch is pre programmed and shipped in an anti static bag Do not remove the devices from their protective anti static bags until you have taken precautions against static discharge If possible use an anti static wrist strap and conductive mat These can be purchased readily from electronic retailers If these are not available then at least ensure you have discharged yourself by touching an earthed met...

Страница 3: ...standing options 16 7 2 Using the rotary encoder 18 7 3 Configuration Preview 18 7 4 Entering New Values 18 8 Installing in a MST 20 8 1 Front Panel 20 8 2 Wiring 21 8 3 Power 21 8 4 Output 21 9 Operation 22 9 1 Power on 22 9 2 Tuning 22 9 3 Frequency steps 22 9 4 RIT 22 9 5 Voltage Display 22 9 6 Frequency calibration 23 9 7 Voltage display calibration 23 10 Notes 24 10 1 Overclocking 24 10 2 DDS...

Страница 4: ...sue 1 Page 4 List of Figures Figure 1 CPU 7 Figure 2 DDS generator 8 Figure 3 LCD Rotary Encoder and Power Supply 9 Figure 4 Component overlay 14 Figure 5 Installing in a MST 20 Figure 6 MST3 cable 21 Figure 7 LCD operating display 22 ...

Страница 5: ...ffecting the transmit frequency 7 Display of power supply voltage 8 Display state of USB LSB and TX RX inputs 9 Programmable IF frequencies Separate high and low side IF frequencies ensure the displayed frequency is the same as the transmitted frequency when changing sidebands 10 Programmable option to save the current frequency and step value into memory These are re loaded at power up 11 Fine ad...

Страница 6: ...ures the incoming power supply rail via a resistive attenuator formed with R5 and R6 The calculated value is displayed on the LCD during use The A input is used to monitor the TX RX state while the D input is used to detect the state of the USB LSB switch The inputs expect a nominal 12 Volt to 0V state change and are buffered by resistive attenuators to protect the microprocessor inputs The PCB al...

Страница 7: ...DDS VFO 2 Construction Manual Issue 1 Page 7 Figure 1 CPU ...

Страница 8: ...DDS VFO 2 Construction Manual Issue 1 Page 8 Figure 2 DDS generator ...

Страница 9: ...DDS VFO 2 Construction Manual Issue 1 Page 9 Figure 3 LCD Rotary Encoder and Power Supply ...

Страница 10: ... resistor R1 R3 R10 1 30K 1 4W 1 resistor R5 1 20K horizontal trimpot VR1 Semiconductors 1 ATmega328 28pin DIP U1 1 AD9834 DDS 20 pin TSSOP U2 1 7805 5V regulator TO220 VREG1 1 50MHz crystal oscillator module XO1 1 16 x 2 LCD with backlight LCD1 Inductors 2 4 7uH moulded RF choke L1 L2 Hardware 1 DDS VFO PCB 1 28 pin DIP narrow IC socket 1 3 pin x 2 row 2 54mm pitch header HDR1 ISP 1 Rotary Encode...

Страница 11: ... DDS VFO is configured for an IF frequency of 10MHz and display frequency of 7 100MHz The DDS computes the output frequency to be 10 000MHz 7 100MHz 2 900MHz The final transmitted signal will be 10 000MHz 2 900MHz 7 100MHz Now let s assume that we want to move the carrier frequency 300Hz higher This could be due to a slightly higher crystal filter response or after testing we find the USB is not s...

Страница 12: ...onents The lesson is to double check the values and orientation of components before installation There isn t a best scheme for loading the components however the suggested procedure is to load the smaller components first and then work upwards 5 2 CONSTRUCTION STEPS Refer to the parts list and Figure 4 when installing the components Step 1 Resistors If in doubt check the values with a multimeter ...

Страница 13: ... mounted on the reverse side with the short ends of the pins located in the PCB Ensure it is pushed in completely and solder the end pins first and check it is at right angle to the PCB before soldering the remaining pins Step 8 Rotary encoder The rotary encoder is mounted on the reverse side Insert into the holes and check that it is at right angle to the board before soldering It is not necessar...

Страница 14: ...DDS VFO 2 Construction Manual Issue 1 Page 14 Figure 4 Component overlay ...

Страница 15: ...nstalled is not the one supplied in the kit the current may be different depending on the backlight characteristics If the readings are way outside this range turn off immediately and look for problems At this stage you may or may not see anything on the LCD Most likely this is because the LCD contrast has not been set Adjust the contrast trimpot until the characters are clear and easy to read Tur...

Страница 16: ...ncy DDS VFO frequency Transmit frequency 80M 10MHz 6 5MHz 3 5MHz 40M 10MHz 3MHz 7MHz 20M 10MHz 4MHz 14MHz 17M 10MHz 8MHz 18MHz Note that the DDS VFO firmware assumes that the DDS VFO frequency is always below the IF frequency If the IF Offset is set to No the DDS output frequency will be the same as the displayed frequency This is the setting selected when the DDS VFO is to be used as a general pu...

Страница 17: ...master clock frequency Due to component tolerances the master clock may not be exact and as a consequence the transmitted signal will be slightly off frequency when compared to the display frequency This option allows trimming of the DDS output frequency in firmware The range is plus and minus 500Hz in 10Hz steps Volts Calibrate The microcontroller measures the battery voltage using an analog to d...

Страница 18: ...ing the encoder button for less than 1 second will toggle between Yes and No Once completed press the encoder button for longer than 1 second and release If this option is set to No the IF Freq High and IF Freq Low menus will be bypassed 5 The IF Freq High menu will be displayed and the cursor will be positioned on the 10MHz digit Rotating the encoder clockwise increments the digit while rotating ...

Страница 19: ...displayed Rotating the encoder clockwise increments the value while rotating the encoder anti clockwise decrements the value Pressing the encoder button for less than 1 second will toggle the plus minus sign Once completed press the encoder button for longer than 1 second and release 11 The Volts Calibrate menu will be displayed Rotating the encoder clockwise increments the value while rotating th...

Страница 20: ... nuts A countersink screw is used on the front panel to provide a flush surface for the front panel label to sit If preferred round head screws can be used which means that holes need to be made in the label and also the heads will be visible from the front If a LCD is used that does not incorporate a backlight it will not be as high and so the length of the screws and spacers need to be reduced a...

Страница 21: ...ble The MST3 end is terminated with a 6 pin plug with only 4 pins used The DDS VFO end is terminated in a 4 pin plug The connections are shown in Figure 6 Figure 6 MST3 cable 8 4 OUTPUT The DDS VFO output is via a 2 pin connector The ground pin is indicated with a G on the PCB overlay MST3 DDS VFO GND 12V RX TX USB LSB ...

Страница 22: ...e available steps which are 10KHz 1KHz 100HZ and 10Hz 9 4 RIT In receive mode press the button down for longer than 1 second RIT will be displayed on the bottom line The frequency can now be adjusted independent of the transmit frequency When switching to transmit mode the DDS will revert to the transmit frequency To exit RIT press the encoder push button for longer than 1 second The RIT message w...

Страница 23: ...ating the encoder will increase or decrease the difference value 6 Once set press the encoder button for longer than 1 second 9 7 VOLTAGE DISPLAY CALIBRATION 1 Measure the power supply voltage and compare this to the voltage displayed on the LCD Note the difference 2 If the power supply voltage is less than the displayed voltage the difference needs to be subtracted in the Volts Calibrate configur...

Страница 24: ...ange is not limited by the firmware but there is a practical limit set by the hardware The AD9834 is clocked by a 50MHz master clock and the maximum usable frequency is 1 4 of this or 12 5MHz Also the DDS VFO hardware incorporates a LPF with a 10MHz cutoff frequency and any frequencies higher than this will be greatly attenuated The DDS VFO does not limit operation beyond the amateur bands It is u...

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