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Help understanding SNR of a radio reciever

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BobK

Jan 5, 2010
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However, I thought it was kind of cool to pick up a morse code beacon and have it tickle a feedback loop with the guitar. (If indeed that is what was really happening). If could see this worked into an indie rock hit.

Bob
 

dietermoreno

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However, I thought it was kind of cool to pick up a morse code beacon and have it tickle a feedback loop with the guitar. (If indeed that is what was really happening). If could see this worked into an indie rock hit.

Bob

Wait, but I thought you said what I have built is not a regenerative receiver and it only works because those stations are so close?

How would any RF feedback loop be formed when the audio mixer demodulates the feedback into audio so it is an audio feedback loop?
 

dietermoreno

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Wireless electric current? Tesla was right?

Wireless electric current? Tesla was right?

Here in this video

My guitar can pick up an unmodulated audio signal from an audio cable using the audio cable as an antenna, and using an audio mixer to step up the current to a high enough transmission level, with the cable not even touching the pickups!

"Wireless electric current".
 

(*steve*)

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How would any RF feedback loop be formed when the audio mixer demodulates the feedback into audio so it is an audio feedback loop?

I will repeat... "Anything can be a crappy antenna if your wiring is shoddy enough, even a guitar."
 

(*steve*)

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My guitar can pick up an unmodulated audio signal from an audio cable using the audio cable as an antenna, and using an audio mixer to step up the current to a high enough transmission level, with the cable not even touching the pickups!

I'm not going to even look at it at the moment.

but my conclusions are:

1) here we go again
2) It's crosstalk
3) I will repeat... "Anything can be a crappy antenna if your wiring is shoddy enough, even a guitar."
 

dietermoreno

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I will repeat... "Anything can be a crappy antenna if your wiring is shoddy enough, even a guitar."

Okay I get the idea that anything with crappy wiring can be an antenna!

That didn't answer my question of how an RF feedback loop can be formed with a guitar when the feedback loop is an audio feedback loop since the guitar is connected to an audio mixer whose output is connected to its input and its output is also connected to the guitar amp as the audio amplification stage with the audio feedback loop as the detector stage and audio pre amp stage.


So tell me, what have I built if on higher frequencies (less pickups selected) (presumably VHF) when I overdrive the mixer to oscillation I hear morse code beacons nearby my house that are loud enough to be recorded by my camcorder's microphone, and on lower frequencies (more pickups selected) (presumably MW) when I don't overdrive the mixer to oscillation I can faintly hear news anouncer's voices only with my ear pressed against the speaker cabinet and its not loud enough to be recorded by my camcorder's microphone and all the stations are a jumbled mess interfering with each other so I hear like 5 different voices at the same time and none of the voices are intelligible compared to only the morse code is intelligeble?

That kind of sounds like a regenerative receiver to me, from the videos of regenerative receivers that I have watched on YouTube? but how did I make it work when I am using an audio feedback loop instead of an RF feedback loop?

Unless perhaps my accidental use of TRS cables since that's all I had instead of instrument cables, that is accidently forming an RF feedback loop at the same time as the audio feedback loop since only one channel on the TRS is connected and the other can carry RF like an antenna, and the TRS antenna parts in a loop next to each other "tickle each other"? So I accidently built a regenerative receiver correctly even though I didn't know I was building it correctly?

I wonder if it wouldn't work anymore if I bought instrument cables instead of TRS cables and tried connecting them, and then all I would hear at mixer overdrive oscillation is a whine hurting my ears, rather than the whine beeping on and off.
 
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davenn

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we told you weeks ago in another post how it happens
its nothing magical ... cable between guitar and amp with maybe a little help of the wiring in the guitar, bringing the RF signal down into the amp. Where it meets a diode junction, maybe in one of the pre-amp transistors, the audio gets detected and amplified by by later stages of the amplifier
nothing more, nothing less ... just one of those things that occassionally happens when there is a nearby strong RF transmitter

I doubt that there is anything regenerative about the detection and amplification
there doesnt have to be to get the results that you are hearing

Dave
 

davenn

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I'm going to put this thread to bed, as it should have been many posts ago


cheers
Dave
 

(*steve*)

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There is just one more thing that can be said on this.

If you have 2 conductors in close proximity, and one is carrying [an AC] signal, the magnetic field created by that signal can cause the signal to appear in the second wire.

This is almost always undesirable and is the reason for shielded cables etc.

This is a way to get audio from one cable to another, but it is not radio! It is simple induction.

It's undesirable, and crappy wiring is also often a cause.
 
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