If you want a connected to PC SunSDR to receive announced characteristics, you will have to calibrate it. For that it is necessary to connect to antenna’s input standard-frequency generator with previously known frequency and amplitude. But in most cases such device isn’t on tap. The problem can be solved with the easiest quartz crystal-controlled generator, which is used to calibrate the synthesizer, S-meter and to reject the image in SunSDR transceiver.
Schematic diagram is given at the figure 1.
Figure1 - Schematic diagram of calibration generator
At the basis of this construction lies quartz SMD square wave generator with the span of ~1.5 V. The signal is rejected by attenuator with output resistance 50 ohm. At the output there appears signal’s effective value, nearly -63 dBm, which is enough for calibration. But beforehand it is necessary to indicate in the program signal’s level and frequency.
If you made the generator by yourself, signal’s level at the output can vary (because of element’s different parameters), that’s why it is recommended to measure output signal level after the mounting by precision tool (spectrum analyzer, selective voltmeter, transceiver, etc.) and sign this value in the program. Stable work of generator needs power from stabilized source, voltage 3,3 V and current not less than 30 mA.
For unassisted production of generator according to “laser-ironing” technology was developed double-sided printed circuit. Pictures of both sides are given at the figure 2, elements layout at the circuit board at figure 3, list of components in table 1.
Figure 2 – Top side (left, mirror imaging) and bottom-side (right) of circuit board
Figure 3 – Elements layout at the circuit board
|С1||10μFх10V||Tantalum chip capacitor, case type -B|
|С2||0.1 μF||Chip capacitor, dimension-type 0805|
|G1||Battery box CR2032|
|R1||1.5 kOhm||Chip resistor, dimension-type 0805|
|R2, R5||51 Ohm||Chip resistor, dimension-type 0805|
|R3||2,2 kOhm||Chip resistor, dimension-type 0805|
|R4||300 Ohm||Chip resistor, dimension-type 0805|
|XS1||BNC||Corner jack for a board|
|Z1||CO4305-25.000||Quartz crystal-controlled generator 25 MHz from company Ralton|
In this article there was given a construction of the easiest calibration generator for SunSDR transceiver. There was developed circuit board to revise the construction on your own. We hope that this article will help you to assimilate Software Defined Radio technology.