Holy Broadband Noise, Batman!

A project log for LowFER Transmitter for your Arduino

Transmit on the license free Longwave band using your Arduino!

casey-halversonCasey Halverson 07/27/2015 at 07:180 Comments

Our spectrum analyzer only goes down to 10MHz, but as you can see, the Arduino PWM generated a ton of noise! The top of the spectrum analyzer is -20 dBm, so while we might have been in good shape, some of the harmonics in the LW and AM band were probably not in compliance.

To fix this, I ordered some components to assemble a low pass filter off Digikey. Once these show up, I will demonstrate how well our spectrum has cleaned up!

Also, for fun, I ordered some programmed crystal oscillators at some specific frequencies for all of the experimental bands (along with low pass filters). We can use the Arduino to turn this oscillator on and off with a GPIO pin, allowing us to use bands that are out of reach of the Arduino PWM to generate CW.

Crystal oscillators are fun because they generate square waves when powered. These square waves can be surprisingly powerful. Driving a crystal oscillator at 12 volts can produce a quarter watt if you are not careful!

Stay tuned for some Arduino PWM LowFER (160-190 KHz) and MedFER (525-1705 kHz) examples, along with some HiFER (13.56 MHz) and 49er (49.82-49.90 MHz) using these cool crystal oscillators.

We did neglect one band that doesn't have a name yet (26.960 MHz - 27.280 MHz), but that falls within the CB band and might be a bit boring.

Remember, these are all part 15 bands. Assuming you follow the rules, they are completely legal to use without a license. Thats right, you could potentially talk around the world without an amateur radio license. How weird is that?