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Radio Antenna signal 'sound art project'
Old 6th March 2014
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djtoshi182's Avatar
🎧 5 years
Radio Antenna signal 'sound art project'

It is my pleasure to find this forum, since I have been looking for any kind of solution for my project with lack of understanding on signal processing.

I am making an art project using a typical radio antenna. (pic)
I want to make this antenna to generate a static sound thru a speaker.
I don't want it to be a fully functional radio with all the hardware parts.
When you swivel or touch the antenna from tv or radio, you get a bad signal reception, and generate a static noise.
I will install many of this radio antenna suspended from the ceiling, so it's static/non-static sound gets shifted when the audience walks by or touch it directly. (just like a Theremin - you don't touch the antenna,coil, but its sound shift)

I do not know the hardware like transmitter, amplifier, receiver etc. from the radio. I guess this needs an amplifier to be connected to the speaker.
I was thinking to use a contact mic or a phone pickup mic with a preamp, but I wonder if it collects any noise signal?
How can I make this antenna gathers a static signal, so simply generates its noise thru the speaker?

Could you PLEASE tell me which equipment is minimally needed to make this antenna work as a sort of basic Signal Theremin?

I hope someone could guide me a bit despite of my lack of understanding on radio.


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Radio Antenna signal 'sound art project'-screen-shot-2014-03-05-11.31.21-pm.png  
Old 6th March 2014
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Lotus 7's Avatar
If you just connect a antenna to an audio amplifier, you will get a lot of hum and possibly a little "static " noise when someone touches it or gets very, very close (a fraction of an inch). You can also expect to get some very loud "clicks" and "pops" when the antenna is touched, due to discharge of the electrostatic charge most moving humans carry.

To pick up the typical "static" sound that is associated with a radio, you actually need a radio.

It doesn't have to be anything fancy, just a radio which is tuned between stations with the gain (volume) turned up. that will provide a background "hiss" and some electrical noise depending on what electrical equipment is in the vicinity. The noise may change somewhat as people move near the antenna, but don't expect anything dramatic.

An AM radio will generally pick up more noise from nearby electrical equipment, but it will be difficult to find one that has a connection for an external antenna. Most small AM radios use an internal ferrite rod antenna, even if they have a telescopic antenna built in, the telescopic antenna is usually only for the FM and short-wave bands if the radio has them. It wont affect the AM section.

Your simplest solution (one that doesn't require any engineering knowledge or construction of special circuits) would probably be to just get an older (non-digital) FM radio (one that allows tuning between the regular station frequencies) and connect its headphone output to an audio amplifier. connect your hanging antenna to the radio's built in telescopic antenna, but keep the one in the radio retracted. The US FM radio band is one that has wavelengths of a few meters, so persons within those distances (a few meters) can affect the amount of reflected radio signal reaching the antenna. and change the noise level as the FM limiting and automatic gain control change with the signal strength. Again, don't expect dramatic changes as persons approach and move away from the antenna.

With additional circuitry, you could, in fact, have the noise level change dramatically using the same sort of RF controls that a Theremin uses to change the sound frequency with one antenna and the sound amplitude with the other. However, that requires constructing some, not trivial RF circuitry, and is not a job for a beginner.

It would actually be simpler to build a circuit that controlled the volume of a noise source (or any audio signal, like a pre recorded sound track) driving an audio amplifier with a photo cell that was positioned to pick up reflected light from a passing person, or was positioned so that the passing subject blocked an invisible infrared beam from an IR LED.
Old 6th March 2014
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djtoshi182's Avatar
🎧 5 years
Thank you for your reply.

Then, can I connect multiple antennas into a single radio for a multiple signal reception? or will it sounds same as with a single antenna?
Old 6th March 2014 | Show parent
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Lotus 7's Avatar
Originally Posted by djtoshi182 ➑️
Thank you for your reply.

Then, can I connect multiple antennas into a single radio for a multiple signal reception? or will it sounds same as with a single antenna?
Adding more antennas may increase the amount of constant noise, but multiple antennas won't pick up "more" or different signals. A standard (unmodified) radio will limit your reception to one narrow frequency range and you will receive whatever noise happens to be on that frequency.

Adding several antennas will also make the signal less sensitive to change when someone approaches the antenna since the radio signal will sort of average out from the signals being picked up by each antenna segment. If you have (5) antennae, each antenna contributes 20% of the signal and if a person changes the signal on one antenna by half, the total signal only changes by 10%. If you have only one antenna, and it's signal changes by half, the total signal also changes by 50%.

Combining signals from multiple antennae is actually used to reduce noise pick up and increase received radio signal strength due to signal sources moving.
Old 6th March 2014
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djtoshi182's Avatar
🎧 5 years
Thanks for the info.
I could somewhat amplify the gap of signal difference, but limiting reception is problem. If antennas are connected to each different radios (maybe different freq), will antennas get interfered by other antennas, or a person in near?
I want the viewer to be a sort of spatial interference to the signal reception field of antennas. so he can feel the signal conflict more audibly.

plus, could you please tell me which cable do I need to use to connect between hanged antenna and the one from the radio?

much thanks!
Old 6th March 2014
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Lotus 7's Avatar
Having different anntennas on different radios won't interfere with each other, but the effect may be similar as one approaches each antenna. You will be picking up a combination of atmospheric radio noise (which may be coming from hundreds of miles away) and local RFI (radio frequency interference) which may be caused by a computer in the next room or a truck going by across the street. The sound coming from the audio output of a receiver will be a combination of many sources and is unpredictable. It will depend on local conditions. It's noise after all.

Having different antennas on radios tuned to different frequencies will will have different spatial effects, but the noise will be essentially the same. If there's a local source of RFI, it will probably be picked up equally by all of the radios.

As I mentioned, you will not get a dramatic effect with just an antenna or several connected to different radios. Having a audio "expander" in the audio signal path before the audio amplifier can enhance the effect of the signal changing as people move around near the antenna(s).

If the antennas are going to be located more than a few feet from the radio receivers, you can't just use plain wire to connect. For the US FM band, the first 4 or 5 feet of wire will become the effective antenna and anything beyond that will have little effect as an antenna.

To connect a "remote antenna", you must use shielded cable. For the radio frequencies involved the correct cable is called "coax" (coaxial cable). It has a center conductor that can carry the antenna signal, but to function correctly its outer shield (which is usually made of braided fine copper wires) must be connected to the radio ground. That would be the metal chassis on a larger radio or the ground conductor on a smaller, battery powered radio's printed circuit board. On a small portable radio, usually, the only access point to the radio's ground conductor (or ground plane) is the outer contact of the earphone jack. The coax outer conductor (the shield braid) is only connected at the radio. Leave it unterminated at the antenna end, but be sure it's trimmed so it does not short to the antenna. The antenna itself is connected to the coax center conductor, and the coax center conductor is connected to the (retracted) antenna on the radio.

Using coaxial cable, the antenna can be many feet away from the radio receiver. You may find shielded audio cable, but that won't work very well for an antenna, it should be real "coax".

The other possibility is to use small portable radios and locate them at the antennas. Then use longer audio output cables to get the signals to your mixer and audio amplifier.

Be sure that the radio(s) you choose do not have automatic noise muting. Some "better" FM radios have built-in circuits that mute the audio output if the radio is not tuned to a strong, noise-free station. If the station signal strength drops, the radio mutes its output rather than subject the listener to a burst of noise. Obviously, that's not what you want.

If I were doing such a project, I'd do it optically. I'd use a recording of "white" or "pink" noise, or a repeating, long loop of off-the-air radio noise (if you want something "dirtier") and send it though several CDS photo-cells connected to an audio voltage divider. I'd illuminate the cells with an invisible IR beam the would be reflected by people moving by. That would result in a much more consistent system response.

However, I'm not an "artist", only an engineer, and engineers like predictable systems.
Old 13th March 2014
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djtoshi182's Avatar
🎧 5 years
Thank you, Lotus 7
your advices are really helpful.

I am going to try one of analogue shortwave radio, with audio expander for connecting multiple antennas.
I really like the quality of noise signal from the shortwave radio. so would like to amplify that as much as possible.
also thinking what would happen, if antenna would get any static noise when it placed closely to the external coaxial speaker. will there be a signal interference just like the speaker and the microphone get close to each other.
I am trying to avoiding audio playback from the pre-recorded sound.. to go in live.

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