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9/22/2017 12:11:25 AM
Posted: 4/3/2006 5:32:03 PM EDT
[Last Edit: 4/3/2006 5:46:37 PM EDT by CAR-10]
So I was in the process of connecting my cable TV coaxial in to my computer. I first made the connection to the computer, then I was mating up the coaxial to the signal splitter and I sensed the flow of a small amount of electricity, definitely not 120. So much voltage that when I forced myself to make contact with both the splitter and with the end of the coaxial I got a warning light on my computer's two surge protector strips.

I live in an older house on an AFB so the wiring isn't splendid. I had to use a ground plug adapter to even be able to use the surge protector strips.

Additionally, the Comcast guy hooked up a signal amplifier to this specific line into the house. Does that add voltage to the cable?

And...my internet connection uses this same cable connection except it goes through a cable modem then through a US Robotics Router.

So what the hell? Does this mean I shouldn't make the connection? Do any of you guys have any suggestions for fixing the problem?
Link Posted: 4/3/2006 5:34:59 PM EDT
Yes, I think like 40-60 volts, but very low amperage.
Link Posted: 4/3/2006 5:35:13 PM EDT
May have to do with an improper install, like something isn't grounded maybe. I am no expert on wiring and I'm sure someone better will come along, but when the satellite people installed my stuff, one of the coax cables coming in always had a current running through it that I could feel if I ever had to unscrew it.
Link Posted: 4/3/2006 5:36:26 PM EDT

Originally Posted By CAR-10:
So I was in the process of connecting my cable TV coaxial in to my computer. I first made the connection to the computer, then I was mating up the coaxial to the signal splitter and I sensed the flow of a small amount of electricity, definitely not 120. So much voltage that when I forced myself to make contact with both the splitter and with the end of the coaxial I got a warning light on my computer's two surge protector strips.

I live in an older house on an AFB so the wiring isn't splendid. I had to use a ground plug adapter to even be able to use the surge protector strips.

Additionally, the Comcast guy hooked up a signal amplifier to this specific line into the house. Does that add voltage to the cable?

And...my internet connection uses this same cable connection except it goes through a cable modem then through a US Robotics Router.

So what the hell? Does this mean I shouldn't make the connection? Do any of you guys have any suggestions for fixing the problem?



How did you sense it? Did you put a voltage meter on it or something?

Yes there is voltage on Cable TV. I don't know the specs for the signal, but there is a voltage there.
Link Posted: 4/3/2006 5:36:27 PM EDT
Im not a cable guy but Im sure it has some electricity running through it. Telco does though and I know they have to use PGE when they hook up Telephony.

Telco is 52 volts but its DC, some AC is used to ring the phone though. Like I said Im not a cable guy.
Link Posted: 4/3/2006 5:36:54 PM EDT

Originally Posted By dolanp:
May have to do with an improper install, like something isn't grounded maybe. I am no expert on wiring and I'm sure someone better will come along, but when the satellite people installed my stuff, one of the coax cables coming in always had a current running through it that I could feel if I ever had to unscrew it.


Cable for sat has voltage for the LNB.
Link Posted: 4/3/2006 5:37:07 PM EDT
Might be something wrong with the amplifier. Hook up a meter and check the voltage on the coax.

Cable tv lines only run at 18vdc here.


Link Posted: 4/3/2006 5:37:59 PM EDT

Originally Posted By ffsparky26:

Originally Posted By CAR-10:
So I was in the process of connecting my cable TV coaxial in to my computer. I first made the connection to the computer, then I was mating up the coaxial to the signal splitter and I sensed the flow of a small amount of electricity, definitely not 120. So much voltage that when I forced myself to make contact with both the splitter and with the end of the coaxial I got a warning light on my computer's two surge protector strips.

I live in an older house on an AFB so the wiring isn't splendid. I had to use a ground plug adapter to even be able to use the surge protector strips.

Additionally, the Comcast guy hooked up a signal amplifier to this specific line into the house. Does that add voltage to the cable?

And...my internet connection uses this same cable connection except it goes through a cable modem then through a US Robotics Router.

So what the hell? Does this mean I shouldn't make the connection? Do any of you guys have any suggestions for fixing the problem?



How did you sense it? Did you put a voltage meter on it or something?

Yes there is voltage on Cable TV. I don't know the specs for the signal, but there is a voltage there.



It was like licking a 9V battery, except through my fingers.
Link Posted: 4/3/2006 5:40:34 PM EDT
Typical CATV coax will have an AC voltage on the pin. Damn near all satellite TV will have DC voltage on the conductor. It will be lower voltage and extremely low amperage. Since analog cable tv utilizes an analog signal (AC frequency heterodyned with a signal) that frequency must have a potential (voltage between pin and shield) to be able to produce a useable signal at the end. Due to a required signal to noise ratio, the voltage must be high enough to overcome line loss and high enough to accomodate bandwidth adequate enough to maintain a decent Bit Error Rate.

Long story short: Voltage = OK
Link Posted: 4/3/2006 5:40:55 PM EDT

Originally Posted By Hedonist:
Yes, I think like 40-60 volts, but very low amperage.



My guess (not that I have calibrated fingers) would be somewhere around 30V.

I've been shocked by stuff enough times to have something to compare it to.
Link Posted: 4/3/2006 5:41:08 PM EDT
Wrong you could unhook your Cabletv or sat. and stick you tongue on it and not feel a thing
Link Posted: 4/3/2006 5:42:57 PM EDT

Originally Posted By Wingnut116ACW:
Typical CATV coax will have an AC voltage on the pin. Damn near all satellite TV will have DC voltage on the conductor. It will be lower voltage and extremely low amperage. Since analog cable tv utilizes an analog signal (AC frequency heterodyned with a signal) that frequency must have a potential (voltage between pin and shield) to be able to produce a useable signal at the end. Due to a required signal to noise ratio, the voltage must be high enough to overcome line loss and high enough to accomodate bandwidth adequate enough to maintain a decent Bit Error Rate.

Long story short: Voltage = OK



So what you're saying is I should be alright if I decide to hook the coax up to my computer? I probably won't fry anything out? What about the warning light I get on the power strip? Couldn't this be the result of a bad ground?
Link Posted: 4/3/2006 5:43:43 PM EDT

Originally Posted By Carhlr:
Wrong you could unhook your Cabletv or sat. and stick you tongue on it and not feel a thing



Wrong, at least for the satellite side, a voltage of 12-24VDC is provided on the center conductor to provide bias voltage for the low noise block amplifier (LNB). Generally the LNB's require no more than approx 400mA but thats still enough to feel it.
Link Posted: 4/3/2006 5:46:19 PM EDT
Does you cable provider offer digital telephone? Phones need more power then a standard cable signal.

Ever been working on a telephone jack when someone calls in?
Link Posted: 4/3/2006 5:48:05 PM EDT

Originally Posted By Synister1:
Does you cable provider offer digital telephone? Phones need more power then a standard cable signal.

Ever been working on a telephone jack when someone calls in?




That old ding-a-ling bell needed some strong juice to ring.
Link Posted: 4/3/2006 5:51:05 PM EDT
If you don't have a ground at your receptical, you might as well throw your surge protecter away.
It won't have anywhere to shunt a spike to.POOF
I would say worry about getting a ground source before anything else.
Link Posted: 4/3/2006 5:51:19 PM EDT
Link Posted: 4/3/2006 5:52:31 PM EDT

Originally Posted By Hedonist:

Originally Posted By Synister1:
Does you cable provider offer digital telephone? Phones need more power then a standard cable signal.

Ever been working on a telephone jack when someone calls in?




That old ding-a-ling bell needed some strong juice to ring.



My dad's a phone guy, I'm sure he's been juiced. I don't think Comcast is offering phone service yet, not sure though.
Link Posted: 4/3/2006 5:53:01 PM EDT
[Last Edit: 4/3/2006 5:55:00 PM EDT by Wingnut116ACW]
I like pie

Double tap, updated info below.
Link Posted: 4/3/2006 5:53:20 PM EDT
[Last Edit: 4/3/2006 5:54:08 PM EDT by Paul]
Link Posted: 4/3/2006 5:54:10 PM EDT

Originally Posted By CAR-10:


So what you're saying is I should be alright if I decide to hook the coax up to my computer? I probably won't fry anything out? What about the warning light I get on the power strip? Couldn't this be the result of a bad ground?



You SHOULD be okay. What probably occured is your cable was right on the fringe of making an adequate BER so to improve your S/N, a line amp was installed to boost your S/N and therefore voltage on the line. What is probably happening is the voltage on the line is a bit higher than the surge protector is used to seeing. Why are you running it through a power strip surge protector? If your amplifier doesn't have a surge protection circuit built in, a stand alone surge protector is probably your best bet.

YMMV you SHOULD be okay but I am only a satcom guy, my CATV skills are shady, I will ask some folks from Scientific Atlanta to see what they can tell me tomorrow.
Link Posted: 4/3/2006 5:55:14 PM EDT
The first thing your coaxial cable should hit before entering your home is a grounding block. From there it can then be split, amplified, or whatever. If it does not hit a grounding block (with wire runing to an earth ground) you run the risk of blowing anything past that when surges blow through.
Link Posted: 4/3/2006 6:00:50 PM EDT

Originally Posted By Wingnut116ACW:

Originally Posted By CAR-10:


So what you're saying is I should be alright if I decide to hook the coax up to my computer? I probably won't fry anything out? What about the warning light I get on the power strip? Couldn't this be the result of a bad ground?



You SHOULD be okay. What probably occured is your cable was right on the fringe of making an adequate BER so to improve your S/N, a line amp was installed to boost your S/N and therefore voltage on the line. What is probably happening is the voltage on the line is a bit higher than the surge protector is used to seeing. Why are you running it through a power strip surge protector? If your amplifier doesn't have a surge protection circuit built in, a stand alone surge protector is probably your best bet.

YMMV you SHOULD be okay but I am only a satcom guy, my CATV skills are shady, I will ask some folks from Scientific Atlanta to see what they can tell me tomorrow.



That's the funny thing, I'm not running it through the surge protector. Just straight from the wall split into a cable modem and into two coaxials that each go into a TV. The second of the TV coaxials is the one that I was trying to plug into the computer so I could use Media Center to watch TV and possibly record TV.
Link Posted: 4/3/2006 6:05:46 PM EDT
okay, that being the case look at the splitter. If it is a 3dB splitter you should have two taps coming from one input. See if there is a DC Pass output. If so, use the other (DC block) to run to your computer just in case. If there isnt one that says DC Pass, look for a capacitor symbol on your splitter --||-- and use that since it is capacitively coupled and therefor blocks DC.
Link Posted: 4/3/2006 6:13:20 PM EDT
voltage does not run


current does
Link Posted: 4/3/2006 6:24:26 PM EDT
[Last Edit: 4/3/2006 6:29:36 PM EDT by CAR-10]

Originally Posted By Wingnut116ACW:
okay, that being the case look at the splitter. If it is a 3dB splitter you should have two taps coming from one input. See if there is a DC Pass output. If so, use the other (DC block) to run to your computer just in case. If there isnt one that says DC Pass, look for a capacitor symbol on your splitter --||-- and use that since it is capacitively coupled and therefor blocks DC.



I don't have any markings to either effect.

I don't have this splitter, I have 56-1942:


I did investigate further and the amplifier apparently adds 12v and it is grounded to the pipes of my hot water heater. So I think I'm going to make the connection, but not until next week when I get back from vacation. ETA: I'll look for a DC block splitter while I'm out and about - that seems to be sound advice.

Thanks for all of your help Wingnut, I'll let you know if I screw anything up.
Link Posted: 4/3/2006 6:36:03 PM EDT
The amplifier probably uses 12VDC to amplify the CATV signal. If it is putting 12 V on your coax, I am stumped. Generally if it is amplifying, it will give a gain expressed in Decibels (dB). Someone please correct me if I am wrong, but regular cable TV should not have a DC voltage on the conductor, only the signal (AC). I will talk to some CATV engineers I know just to double check. Hell, get satellite TV, I can help you with that.
Link Posted: 4/3/2006 6:58:08 PM EDT

Originally Posted By Wingnut116ACW:
The amplifier probably uses 12VDC to amplify the CATV signal. If it is putting 12 V on your coax, I am stumped. Generally if it is amplifying, it will give a gain expressed in Decibels (dB). Someone please correct me if I am wrong, but regular cable TV should not have a DC voltage on the conductor, only the signal (AC). I will talk to some CATV engineers I know just to double check. Hell, get satellite TV, I can help you with that.



You're probably right about it using 12V not sending 12V out. It does say that there is a db gain.

I'd like to get sat TV, but the internet connection seems to be slower. I think I've got a package deal right now. I'll be looking into that shortly.
Link Posted: 4/3/2006 7:03:54 PM EDT
voice signal voltage on telco is minimal. But the ringer voltage is around 90, that's what gets your attention if a call comes in.
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