Author Topic: 450 volts on internet coax line!  (Read 1734 times)

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Offline testtube44Topic starter

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450 volts on internet coax line!
« on: May 14, 2019, 03:44:48 am »
Why does my oscilloscope measure 400+ AC volts on my internet coax line? Yet I short it to ground and it doesn't arc over or anything? I was scared shitless to touch it, what is causing this?
« Last Edit: May 14, 2019, 03:52:28 am by testtube44 »
 

Offline testtube44Topic starter

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Re: 450 volts on internet coax line!
« Reply #1 on: May 14, 2019, 03:49:45 am »
I'm afraid that if I touch it I will die. What is this? EDIT: its mains at 60 hz, not RF
« Last Edit: May 14, 2019, 06:56:28 pm by testtube44 »
 

Offline soldar

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Re: 450 volts on internet coax line!
« Reply #2 on: May 14, 2019, 09:46:18 am »
What happens if you connect a resistor of say 100K or 200K? Still same voltage?
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline StillTrying

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Re: 450 volts on internet coax line!
« Reply #3 on: May 14, 2019, 10:39:36 am »
Going by your other posts I'd have to ask what you're connecting the scope's GND clip to!
« Last Edit: May 14, 2019, 11:01:45 am by StillTrying »
.  That took much longer than I thought it would.
 

Online stj

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Re: 450 volts on internet coax line!
« Reply #4 on: May 14, 2019, 11:54:36 am »
it could be capacitive coupling to a powerline in the street because of shit earthing at the cable mux gear,
put a multimeter across the coax.
btw, is this solid, or oscillating at a fixed frequency?
 

Offline radiolistener

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Re: 450 volts on internet coax line!
« Reply #5 on: May 14, 2019, 12:41:12 pm »
400Vpp at 50 Ohm coax line is 1600 W power. This is twice more than microwave owen.
There is no need to touch it, just to be near is enough, because 100 MHz at 1600 W is crazy power.
If you don't feel smell of burning meat, there is no 400V  :D

« Last Edit: May 14, 2019, 12:43:06 pm by radiolistener »
 

Offline testtube44Topic starter

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Re: 450 volts on internet coax line!
« Reply #6 on: May 14, 2019, 08:05:21 pm »
Going by your other posts I'd have to ask what you're connecting the scope's GND clip to!
The coax ground? If there is that big of a difference between my scope and the line, why didn't it arc over? Is it like static electricity where there's voltage but it dissipates quickly?
« Last Edit: May 14, 2019, 08:06:53 pm by testtube44 »
 

Offline james_s

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Re: 450 volts on internet coax line!
« Reply #7 on: May 14, 2019, 08:07:52 pm »
Sounds like user error to me, I don't see any way you'd get 450V even if it's just capacitive coupling. Either way if you don't get a spark when you short it then there is no safety risk.

Static electricity from walking across a carpeted room on a cold day can easily be more than 50kV, it doesn't kill you because the current available is extremely low.
 

Offline langwadt

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Re: 450 volts on internet coax line!
« Reply #8 on: May 14, 2019, 09:11:10 pm »
capacitors in the input filter of an ungrounded scope means it is floating on mains voltage with regards to the grounded internet coax
 

Offline radiolistener

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Re: 450 volts on internet coax line!
« Reply #9 on: May 14, 2019, 09:43:03 pm »
If it's low frequency, it doesn't have to be 50R terminated.

As I know, Ethernet over coax works at least on 10 MHz and requires terminators.

I can charge a tline with 1kV easily at DC, and I won't even feel it if I discharge it with my finger.

For 10 MHz unloaded 1 kV on 50 Ohm line = loaded 500 V on 50 Ohm = 2500 W RF power.
This is more than enough to roast chiken
« Last Edit: May 14, 2019, 09:52:25 pm by radiolistener »
 

Online stj

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Re: 450 volts on internet coax line!
« Reply #10 on: May 14, 2019, 10:40:13 pm »
not ethernet, internet - most likely DOCSIS.
 

Offline radiolistener

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Re: 450 volts on internet coax line!
« Reply #11 on: May 15, 2019, 07:33:24 am »
not ethernet, internet - most likely DOCSIS.

the same for DOCSIS. It doesn't needs 2 kW power in order to transmit the data.
These 450V looks just like induced voltage from mains.
 


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