For radio ga ga’s final, I decided to do a sound installation using brazilian sociologist Luiz Eduardo Soares work about invisibility. His essays published on the book Cabeça de Porco addresses the topic on the light of brazilian society’s perception and stigma over kids that were born and raised in underprevileged communities in Brazil. Working with an apparently empty space, the user gets in a room and is given a listening device.
Through radio transmition and emition, two different frequencies that alternate each other are transmitting synched audio recordings of a woman (reference to the unclear goal of numbers station) reading the essays – in english and in portuguese. As the public walks in the room, the listening device will hop between the frequencies, creating intentional noise to the understanding of the essay by making it understandable/visible or obfuscate/invisible in different areas of the room.
So the first thing I tried was to receive/listen signals with GQRX + RTL-SDR radio set. After a few software updates and installed it worked fine. So I went to the other challenge: to transmit radio signals.
I reached out to the student list and I got this 80s Radio Shack FM wireless mike transmitter. It was very insteresting to see that it all came to be assembled – and how basically to make a radio transmitter is just a matter of putting a bunch of capacitor, resistors and antenna together.
The transmitter works between 91-96 MHz and the “potentiometer” that sets the frequency is very small. It doesn’t give any visual indication of what frequency you are tuned in to, so I had to turn the GQRX on keep on tapping the mic / whistling on it and see where I saw some kind of distortion on the frequency. It really messed up the signal:
After this experiment, I came with it to class and Surya brought a few questions to me: was I able to stabilize the frequency transmission? Is the antenna the right length? How is the output of the transmission and reception (aka what will be the experience)?
So the first thing I did was to use an antenna that was the right size. For the frequency range, the antenna had to be between 3-3.20 m. So I coiled it up and went back to the GQRX to see how the signals would be. This time they were not distorting the whole range and they showed a stronger signal.
And then I decided to experiment and replace the microphone on the transmitter for a jack plug. I plugged it in and turned the transmitter on as well as turned the music on on Spotify.
And this is what I got:
Because I was using the jack plug in to transmit music, I wasn’t able to listen to the GQRX. So I tried using a jack splitter, but it didn’t work – I was listening to both audios (the computer and the radio).
Although the class is over, I really feel motivated to keep on developing this project. There are a lot of things that I should explore (ie soundflower and rpitx), so the next steps are the following:
transmit recorded sounds from transmitter
“anchor” audio to two specific frequencies
control frequency hopping
design user (receiver) device
fabricate transmitter(s) and receiverLeave a Comment