Citizen Band Radio Frequency Interferences

[Lorenzo]

Hi,
a lot of years ago I like to speak with my two-way radio.

Do you know the sounds of those transceiver ? uiii sfi wiwee

may radio work around 27Mhz... but frequences like LF, MF, HF or high frequnces like SHF maybe have more "coloured" sounds.

Do you know how can I reproduce these kind of sounds?

[iopop3]

Prolly not exactly what you're looking for, but have you seen, http://ericarcher.net/devices/tit/ ?

[EdisonRex]

In general, one of the characteristics of "low fidelity" communications such as AM radio, telephone, intercom, tannoy etc is "narrow bandwidth"; all of these technologies had anything but a flat response curve for the actual signal.

For AM radio technologies, without getting too technical, there were three components to the output. One was the actual demodulated signal, usually tuned into a fairly narrow band of 300-3000Hz in order to reproduce voice. Below 300Hz, the main component of sound is noise, and above 3000Hz, the main component are artifacts of the demodulation (sidebands) and of course noise.

So a bandpass filter 300-3k, some kind of amplitude modulation byproducts, and some good old fashioned noise, in judicious mixing.

[beautyofdecay_]

The best way to get that kind of noises is to use a shortwave radio.
VHF and higher (140MHz and up) usually doesn't have very good propagation of radio waves (reflections in the atmosphere so the radio signal is transported over a very wide range) and you just hear white noise.

Short wave however has very interesting noises, bleeps and digital communications.
Long time ago we recorded a track using an shortwave receiver tuned and detuned to a Morse code transmission, fed into a very long hall effect. It really added a surreal atmosphere to the track.

Great stuff for (random) experimentation

Just look for a second hand shortwave receiver (capable of receiving 1-30MHz), use a long wire as antenna and you're ready to go.

[Lorenzo]

Thank you, EdisonRex!

[LektroiD]

[Lorenzo]

[LektroiD]

Here's a G2 patch, designed for the demo (which you can download here), if you have a hardware G2, let me know and I'll post a full version with mic input

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RadioInterference.pch2
Description:		Download (listen)
Filename:	RadioInterference.pch2
Filesize:	1.02 KB
Downloaded:	1871 Time(s)

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[beautyofdecay_]

What you hear in the youtube movie are USB (Upper Side Band) transmissions. These are so-called single side band (SSB) transmissions where only one side of the spectrum (upper or lower sideband) is transmitted and there is no carrier signal (like with FM transmissions where both sidebands are transmitted).

The "funny" modulation is created when you tune the radio above or below the (suppressed) carrier signal with as result that the audio content is shifted up or down in frequency.

I guess you can simulate that effect by using a pitch shifter.
As the audio bandwidth normally is 3 kHz the higher frequencies are also more attenuated than the lower ones as the audio band is shifted up or down, so that's also something to take into account.
So basically, the audio content is being shifted in frequency while at the same time a low pass filter is being applied.

[Lorenzo]

[Lorenzo]