Inducing RF interference?

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Jungell

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Hello!

I have some questions regarding radio frequency interference and mainly; how do I best go about getting as much of it as possible?
From what I have read, the most common form of RF interference is your typical static noise. But is it possible to receive actual broadcasts, obnoxious host and all?
Which bands are the most common to be picked up by recording equipment; FM, AM or even shortwave?

I am mostly interested in RF interference in hand held digital recorders. Is RF interference an inherit "flaw" in recording equipment and the good ones are just well shielded, or are only some units/brands affected?
How would you go about getting RF interference in a digital recorder? Should I just buy one, an FM transmitter and just turn the knobs until I strike gold?

Basically, I would like to know what you know on this topic.

I ask because I have picked up a new hobby; debunking paranormal claims. This time, it's EVPs that I'm interested in. Disembodied voices in recordings. From what I have read so far, the few EVPs that aren't hoaxes are most likely caused by RF interference, pareidolia or by an actual voice that the paranormal "investigators" just didn't hear themselves. RF interference is also something that I can provide evidence for, so I would very much like your input.

Any help is greatly appreciated.
Thank you!

Jungell
 
I am sorry Jungell but you are obviously totally unqualified to investigate anything caused by RFInterference. You do not for instance seem to know the difference between frequency of transmission and "mode" of modulation? Any transmission frequency can be AM or FM (but most are going to be complex, frequency hopping PCM these days).

You would need to run an RF spectrum analyser with associated recording hardware to keep track of any interfering signals. This data would then need to be correlated to any suspect audio recorded.

The mode by which RF is demodulated in audio electronic devices means that the original RF information (frequency, modulation type) is lost and so just having an audio recording tell you nothing of the source (unless you can recognise the programme).

I remember the hoo-ha about "Raudive voices" back in the 70's as tape recording started as a hobby. For those that do not know...
It was said that if you leave a recorder running in an empty room with a live microphone, sometimes you would find weird, "ghostly" voices on the tape. There was much, quite heated correspondence on the matter over months but none of the "believers" could ever explain why, when at any one time there must be over a million (even then) mics open in thousands of studios, radio stations, TV cont' suites and film lots all over the world all the time, THEY did not have a problem?

To investigate this properly you need to read, learn and inwardly digest all the data on EMC testing and THEN employ the services of a graduate RF engineer!

Dave.
 
Thank you, ecc83!

Yes, I am indeed totally unqualified to investigate anything caused by RF interference. And I realize that I probably came across as rather daft and arrogant as well.
So let me clearify; my intention is not to investigate existing claims and debunk them with knowledge and experience that I clearly do not have. Nor do I think that I can gain this knowledge throughg a few forum posts and wikipedia articles, so I do apologize for that.

My intention is to broadcast my own, easily recognizable piece of audio, and try to tune my transmitter to a frequency that gets picked up by a cheap digital recorder, PC mic or similar. Just to show that it is possible (if it is possible to acrually pick up this kind of audible interference). So my goal is not to prove that any particular recording, said to be an EVP, is RF interference, but just to show that RF interference is a much more likely source. Because like you said, I am horribly unqualified for the former. So before I start experimenting and reading up, to be able to explain the basics, I would just like to know if this kind of interference is possible and how likely I am to be able reproduce it myself?

But you have given me a great place to start... The books!

Much appreciated!
 
Thinking out loud, if OP just trying to capture bleedover :
Would your transmitter allow a linear amplifier, like HAM operators or old CB good-buddies used? Back in the day, many 27MHz (11m) CB'ers, with illegal 1000W linears, would bleed over onto my stereo receiver and/or TV.

Or

You could try building an unshielded mic cable that is the wave length (or partial WL) of your transmitter's broadcast frequency.
 
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So, they sell these things that you can plug into your cellphone's headphone output to transmit it to your car's radio (since it's too old to have an aux jack). Probably the quickest, easiest way to accomplish what I think you're asking for.
 
Ok J!
Well, your first problem is how to generate a high RF field but one that is legal at your 10/20 (ho,ho ho! Rubber duck) and a likely source of interference. It would not be a fair test say to go and sit 100mtrs from "KLMXYZ" putting out 25kW!

No, I think a basic AM CB rig is the best source. Next comes the recording system. Again to be fair a decent dynamic mic, on a balanced XLR cable of course. It would be in order I think to have the mic cable and CE aerial in close proximity, simulating a much stronger signal. To give yourself the best chance of a result I see no reason why you cannot make the XLR cable sub multiples of a 27mHz wavelength? =11.11mtrs.

Thing is of course, the rules (at least here in EC) for RF immunity are now quite stringent so you might struggle to find a "bad" AI! .......A thought occurs? Whilst mic inputs will and should be well RF proofed, makers are often lapse on outputs and the RF can get in that way. Try long (1/2wave?) leads out to monitors.

Mods! Why does my "token" run out please? Bloody infuriating!

Dave.
 
I can't stay logged in for more than five or ten minutes when I'm at work, but my phone and my home computer stay logged in for ever. Don't know if that's the same issue you're having, but it's pretty annoying to start a post, answer a call, and then finish only to find out I can't actually post because I'm not logged in anymore.
 
Wow, thank you for some fantastic suggestions!

It's going to be a lot of fun testing your suggestions and see what comes out of it. Now I just have to wait for my next paycheck to get a collection of recording devices, part from the ones I already have, and the transmitters. Figure I could try both the CB rig and build one of those cheap transmitters for local use, that ashcat_lt suggested. And then just go nuts with a whole slew of setups; poorly shielded cables to the output, cheap external mic, dynamic mic, combinations of bad ideas and so on.

I really appreciate the help. And now it's time to do some more reading on the subject!

I'll let you know how it turns out. And further suggestions are, of course, welcomed!

Jungell
 
Simple approach is to stick your cellphone real close to the recorder and then have someone call it.
CB radio would be really easy - put the recorder near the antenna and transmit. Even without an illegal power amp on it the radio will get into the recorder.

If you know anybody who is into ham radio - they might help you with more ideas (and potentially higher power).
It's generally a lot harder to prevent getting interference than it is to cause it. (sez my 40 years in ham radio....)

Had an acquaintance claim that a part of Colorado was under radio-silence because there were black helicopters seen in the area. And her AM/FM radio didn't receive signals there. I went to the area and concluded that it was because the area was in a lower elevation than the surrounding ground (not quite a valley) and there was no line-of-sight to any broad cast antennas from there. IOW - dirt was shielding the signals.
 
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Ronbert said:
Had an acquaintance claim that a part of Colorado was under radio-silence because there were black helicopters seen in the area. And her AM/FM radio didn't receive signals there. I went to the area and concluded that it was because the area was in a lower elevation than the surrounding ground (not quite a valley) and there was no line-of-sight to any broad cast antennas from there. IOW - dirt was shielding the signals.
Click to expand...

But the black helicopters was a much better made-for-TV story..... :D
 
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