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a few weeks ago I posted about a 180 hz hum in my amp. I finally tracked it down...it's coming from the coax to my nearby cable box/TV. The cable is goes thru what I assume is a wall wart amp, but unplugging it doesn't stop the hum; only physically disconnecting the cable does. Is this common? Can the avg. cable guy deal with it?
Edits: 12/07/14Follow Ups:
I had similar thing here.
Being a hvac tech I looked about and low and behold as I have suspected before not grounded.
Have asked before and been blown off.
Had a Jensen VRD-1FF inline trans on here to.
Worked better but I wasn't satisfied.
System wasn't grounded.
Called cable co, he came looked around even agreed and I said ground it please.
To my surprise he did and now even quieter.
This is VERY common TV is a very dirty signal
If it's not practical to have your cable company properly ground your coax at the entry point to your home, I would go with the other suggestions of trying a coax cable ground loop isolator.
You could try the 75-Ohm to 300-Ohm adapter wired to another identical adapter 300-Ohm to 75-Ohm but that will cause unnecessary signal attenutation (signal loss) vs. a decent ground loop isolator.
The electric code says nothing about practicality or ease of accomplishment. The cable companies are a granted monopoly in the communities they serve and are obligated to do it right. Hell they charge enough for their service!
I agree but if it's not convenient for the home owner for whatever reason, the other solutions will work.
Is your cable drop grounded? Code requires that the cable company ground the input at the service entry. They usual don't do it. I complained to Comcast and they sent out a tech who moved the drop so it entered near the electric service panel and bonded it to the electrical grounding rod - problem solved. Prior to that I was using a 75-300 adapter wired to a 300-75 adapter - both available at RS for a couple of dollars.
Edits: 12/07/14
I doubt that its grounded; it enters at the opposite end of the house from my power box. It was connected before the area was incorporated and code enforcement was pretty loose. The cable co. has said they would move it to the same entry as the power several times but never follow thru.
No surprise. The enforcement of the required code is pretty lax and since no permits are required when the cable company does the install, they pretty much do what they want.
Call your cable company and tell them that they are in violation of code and that you intend to bring them to their knees if they don't fix the problem pronto. Mention that you will call your City Hall requesting that they perform a general inspection of all cable drops in the city and issue citations to the cable providers for all the violations. It may just shake them up. I suspect that if all "illegal" connections were corrected it would run into several millions of dollars in fines and costs.
Up here within a few minutes your signal would be lost and you would call for repair. They would put you on the never fix priority list and enter you on the blacklist so if you go elsewhere the new company will know.you are a trouble maker.
Don Brian Levy, J.D.
Toronto ON Canada
Hum - constant - not dependent on volume level - solved by tying satellite entry block to main service entry - 70ft 8 gauge wire.
"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius
Here's an article on why and how your cable service needs to be bonded to the electric service ground. Eliminating hum is just a nice benefit.
I chased my tail about this for 2 years until I got a newbie technician from the cable company. On my prior calls, the techs tested this and that and blew off my suggestions that they check the location of the cable ground with respect to the service entry.
This guy listened to my suggestion and said, "Why not? I'll give it a try." It took him 20 minutes to check and move the ground. Problem solved for once and for all.
You can try the Ebtech Hum X Voltage Hum Filter, about $50 @ Amazon. I had a bad hum from my Rogue Sphinx and it eliminated all of it.
And good TV Sound, full and lots of Bass.
Image: Holland CISP Cable Isolator - CATV Surge Protection (video cable isolation transformer)
The problem is typical ground loop hum that can be solved via an inline video cable isolation transformer. It's very simple to install.
"Blocks 60 Hz Power up to 5,000 Volts Reduces the Energy Level of Spikes, Eliminates Ground Loop Hum Available with Spike Protection Circuitry (CISP)."
"The CISP separates the coaxial cable ground for DC and low frequency currents while being shielded and transparent to RF signals over 5MHz. It is used by most major cable TV companies around the world where home grounding is not successful and device damage and shock potentials are possible."
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The Holland CISP is a very high quality product that I use as a global filter (inserted at the CATV junction) for a total-home CATV video isolation transformer solution (and much less expensive than the Jensen product).
You can simply insert the CISP between the CATV coaxial cable coming from the wall, and another coaxial cable connected to the coaxial video input jack, or install it within the CATV junction box as I have done.
Best price found: Cable Isolator w/ Spike Protection - $12.49 with free shipping from Cencom.
See link:
MIT made a coax video cable with an isolation transformer to break the ground. I believe Jensen also made one. Call your cable provider, they should also provide such an isolation transformer for no charge.
do you have the cable TV audio out from the box connected to your system? Or some other ground loop
E
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No connection whatsoever. That's why it took so long to track it down. I unplugged the wall wart amp on the coax when originally checking, but the hum remained so I was stumped 'til I tried disconnecting everything in turn in the area...including the coax. Bingo. My neighborhood is at the end of the cable and there are amps for the cable signal each TV (3).
You (or the CATV provider) can install a single inline CATV isolator within the CATV junction box in order to affect all televisions and associated audio systems in your home. If a cable guy for the CATV provider does it, ask him to check the signal after it's installed. You may also be able to ask a CATV customer service agent over the phone to check the signal remotely if you install one yourself.
If your cable box or TV set is connected to your audio system the him can enter ad the coax ground may not be at electrical ground.
No connections between cable and audio system. I tried it once but the analogue audio was out of synch with the HDMI video on the TV.
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