EEVblog Electronics Community Forum
Electronics => RF, Microwave, Ham Radio => Topic started by: MathWizard on July 18, 2021, 12:57:45 am
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I have a cordless landline telephone, and if i stand by the metal kitchen sink, I get good reception, but if I turn on the water tap, which is plastic pipe, running into a stainless steel sink, the reception gets pretty full of static.
The telep. TX is in the basement, about 10ft total from the cordless phone.
So what exactly is going on ?
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I have seen things with non water fluids and plastic that does something like this but never with water, it works like a vandegraff generator
not sure if water can carry a charge, I imagine it depends on purity somewhat
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Do you have an instant-on water heater? If so maybe it has a really noisy triac?
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Hot water system kicking in?
Water pump on property?
In-sink shredding equipment?
Try searching around using an AM radio that's tuned off-station, see if it also picks up the interference when you turn the sink on. Check whether it's really coming from the sink itself or not.
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oh right it could be a switch detecting pressure drop in a tank that turns on a pump with an arcing contact but usually this would just be a burst of interference, but if its a more modern house it could have a noisy drive powering it
but usually its not so quick that would be a bad system, a well usually pressurizes the tank and it holds for a while, and you would notice the interference throughout the day as water is used.
I never seen a shredder that turns on automatically though. Hot water inline heater is a possibility. but keep in mind the office chair oscilloscope ESD discharge.
https://www.youtube.com/watch?v=rv4MjaF_wow (https://www.youtube.com/watch?v=rv4MjaF_wow)
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It may be an audio problem and not an RF problem.
Test by listening to music on hold audio and turning on and off the microphone mute control. I find that cordless phones have very strong echo cancellation on the audio. The audible noise from the running water would be picked up by the microphone and may cause distortion in the incoming earpiece audio due to the echo canceller. If this is true, the earpiece audio will sound normal if the microphone mute control is on.
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Test by listening to music on hold audio and turning on and off the microphone mute control. I find that cordless phones have very strong echo cancellation on the audio. The audible noise from the running water would be picked up by the microphone and may cause distortion in the incoming earpiece audio due to the echo canceller. If this is true, the earpiece audio will sound normal if the microphone mute control is on.
!!!
Splashing/running water has a lot of frequency components in it, this could definitely be it.
EDIT: Another method: record the sound of your sink and play it through some speakers, see if it causes the same problem.
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There's no pump involved, just city water pressure, and the hot water's from a furnace. And it's imediate and contunious static, as soon as the water starts.
Next time I'll see how much flow it takes to be noticeable, but on full flow, it's pretty bad.
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Splashing/running water has a lot of frequency components in it, this could definitely be it.
You see it in every spy movie, when they want to disrupt eavesdropping, they turn on running water :D
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Phone uses audio compression with losses. When you open water, it produce wide bandwidth noise which overloading phone channel bandwidth and most of the useful signal will be lost due to compression loss. Just because wide bandwidth noise cannot be compressed.
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Coincidently, running water is one of those things that really screws up mpeg video encoding too.
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can you put obstructions in the way so it pours into a cup that overflows into the sink or something like that?
does it happen when its just filling a cup, does it happen when the cup over flows, is it different the pouring it directly into the sink? Or a ceramic bowl or something. put a big insulating bowl in there to rule out static charge first. If its still doing interference when its flowing into a bowl and not dripping into the grounded sink that means something.
does muffling the phone audio help at all? get it on a intermediate loudness setting so to test the audio theory you don't completely overload it and give it the opportunity to get louder then when you muffle the phone it would decrease the noise amplitude and change the frequency content.
and then by furnace its a oil? gas? electric? i would turn the water on and go to the furnace with the phone nearby see what happens, thats another thing to investigate after those 2 tests
and you were not clear, is it ONLY the hot water? It would be nice to prove
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I find it interesting because I tried this with a landline phone with 2 sinks and when I put my head into them near the water flow with the phone as much as possible I don't hear anything.
Are you saying the phone does this to the person listening and I should try to call with the phone and pick it up and then listen, or do you hear it on the phone? I know for a fact that RF interference is audible on your headset. I don't know if audio overload does this. Do you hear it or is it a complaint?
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Press the mute button while water is running and see if "static" disappears. If it does you know it is the echo cancellation kicking in.
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forgot phones have one of those
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tried it with 2 phones, having one phone way in the sink you do get a noise that sounds like a fast but somehow chaotic RF sweep jam actually , but I practically had to stick my head way down into the sink with the water, maybe my sink is just particularly quiet and I never noticed it. You might hear that noise if you are trying to scrub the pipe while wearing a headset and you needed to lean way down there for some reason. garbage disposal tech :P