What do you get when you combine a direct digital synthesis (DDS) chip, a power detector, and an Arduino? [Brett Killion] did make that combination and wound up with a practical network analyzer.

The project uses an Analog Devices AD9851 DDS chip clocked at 180 MHz which will output a sine wave at any frequency from 0 Hz and 72 MHz. A Butterworth low pass filter processes the DDS signal and then feeds a two-transistor amplifier. The circuit will output about 0dBm into 50 ohms. The power detector is an Analog Devices AD8307 along with a 50-ohm input load. There is no filtering on the power detector so it can measure from very low frequencies to 500MHz.

[Brett] uses a Python program to process the data from the Arduino. For example, here’s a plot of a 10 MHz crystal from the software:

If you want to know more about DDS, our own [Bil Herd] has you covered (see the video, below). We’ve also seen similar antenna analyzers that are about the same thing.

Network Analyzers are frequently used for measuring filters, making them extremely valuable for building radios and general mucking about with RF. They are, however, extremely expensive. You can, however, build one in an Altoids tin with an Arduino Nano, a small screen, and an AD9850 frequency synthesis module picked up on eBay.

The basic idea behind a network analyzer is to feed a frequency into a device, and measure the amplitude coming out of the device, and plot this relationship over a frequency. [Bill Meara] has been a human network analyzer before, changing frequencies and plotting the output of devices under test by hand. [DuWayne] (KV4QB) build a device to automate the entire process.

The block diagram is easy enough – an AD9850 sends a signal to the device, and this is measured by the Arduino with a small amplifier. The signal is measured again when it comes back from the device under test, and all this is plotted on a small display. Simple, and [DuWayne] is getting some very good readings with a lowpass filter and crystal filter made on a small solderless breadboard.