The author opens up the schematic diagram and supporting Raspberry Pi code. The simulation bandwidth is already 30MHz, and the frequency response is very close to the theoretical simulation, with a difference of about 0.02dB between 1kHz and 30MHz.
This project is a simple scalar network analyzer using DDS, logarithmic amplifier, multi-channel ADC and general purpose I/O interface. The pinout matches a Raspberry Pi, but any microcontroller can be used to program the DDS and read the ADC. The analog bandwidth is intentionally set to 30MHz.
Note how the measured response is very close to the theoretical simulation. There is approximately 0.02dB difference between 1kHz and 30MHz. With the shield installed, the noise floor averages about -69dB.
This circuit is slightly different from most in that in addition to measuring the input voltage from the EUT, it also measures the filtered DDS output. This allows for more accurate measurements as it does not assume the output is constant and any changes due to load effects are automatically compensated for.
| Devices | Class | introduce | Datasheet |
|---|---|---|---|
| AD9850 | semiconductor;The embedded processor and controller | 8-BIT, DSP-NUM CONTROLLED OSCILLATOR, PDSO28 | Download |
| ADS1115 | semiconductor;Analog mixed-signal IC | ADS1115 16-Bit 860SPS 4-Ch Delta-Sigma ADC With PGA, Oscillator, VREF, Comparator, and I2C | Download |
| AD8307 | semiconductor;Analog mixed-signal IC | LOG OR ANTILOG AMPLIFIER, 490 MHz BAND WIDTH, PDIP8 | Download |
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