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# Do a Real Magic Spell: "Essdeeaar!"

Software Defined Radio (SDR) is the wonder child of our times. This project is about understanding, designing, building & playing an SDR.

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SDR seems intimidating at the beginning, but at a closer look it is not so complicated. Like all brilliant ideas, at its core is pretty simple.

The name SDR is not fair. MDR (from Mathematically Defined Radio) or TDR (from Trigonometry Defined Radio) might have been more appropriate, but with a name starting with 'Math', even the most enthusiastic Ham Radio will have stayed away from it.

At the first encounter SDR looks very geeky, but it's addictive too. Just play a little with HDSDR and you are hooked!

The mind immediately starts pouring questions: "How does it works?", "What is this button for?", "How would you do that?". After fiddling with an SDR for hours, after jumping from FM radio to Taxi channel peeping, after sniffing the temperature data from the neighbors weather stations, after looking at the ADS-B airplanes position, start reading the whole Internet in one night.

After reading the whole Internet over night, even more questions pop up: "Now WTF is a constellation?". Oh, forget it!

Building an SDR might clear some things up, but blindly copying an existing schematic would not help too much. Designing one would certainly be more interesting, but this will require to understand the basics.

Understanding SDR requires some math, and all this trigonometry can become very confusing. Some simulations will help understanding. Then, design a schematic and build it.

This is the rough plan.

## FAQ

• What is an SDR? It's a radio. A radio the same as the one used in mobile phones, in Wi-Fi, etc.
• Why it's so special? Because with the same hardware:
• it can receive a wide band of many different frequencies at the same time (same for transmitting)
• can be used with any kind of modulation, for data or audio/video broadcasting
• most of its functionality is implemented in software

• ### Online GeoGebra IQ modulation playground

Interactive IQ modulation and demodulation webpage, with adjustable constant values for I and Q:

https://www.geogebra.org/classic/nymqtwnc

- drag the sliders and observe the changes live
- sliders can be animated
- zoom and pan
- turn functions on/off by clicking the left circles
- edit the functions and play around with ideas and visualization
- can be saved, shared or exported as a picture

The model can be accessed online, as a webpage, no installation required.
(The same model can work offline, too, but only after installing GeoGebra.)

## Get an SDR

A good example for a cheap SDR receiver is an RTL-SDR TV USB dongle. RTL-SDR was designed as a TV tuner for PCs. It can be plugged into a USB port, and with it's software installed it can receive FM radio stations or TV programs.

But with a hacked driver, the same USB dongle can be used as an SDR. And it's cheap, about \$10. This is the little beast:

and this is the tuner chip used by this USB SDR:

Get one, but don't waste your life watching stupid TV broadcasts with it!

## Install HDSDR

HDSDR stands for High Definition Software Defined Radio, and it's a free software that can be used with many SDR tuners.

• download ExtIO_RTL.dll and copy the ExtIO_RTL.dll file into the HDSDR folder (usually "C:\Program Files (x86)\HDSDR")
• start HDSDR and press F2 (Start)

## Play with it, get used with an SDR

3D Printing AVR Arduino Art Audio Automation BeagleBone Bluetooth Cameras Clock Drones Environment Hardware IoT LED Medical Music Radio Raspberry Pi Remote Control Robotics Rockets Satellites Science Security Software Virtual Reality Wearables

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## Discussions

Matthew Rowberry wrote 06/15/2017 at 03:27 point

I want to analyze 2.4 ghz signals. How can I do this? Is there a special receiver for purposes like this? Really interested in this and I hope you post more.

Are you sure? yes | no

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