The curse of cable...

[Boomzilla]

We use Cox Cable (sigh...). Having trouble with phone, internet, and TV the other day, Cox sent a repair "technician" yesterday. He undid everything that the previous Cox visitor had done - removed the coaxial signal amplifier, confiscated the "non-Cox" splitter that I'd installed, bypassed my surge suppressor, and declared "everything's fine." Well, the phone, internet, and TV ARE now working but...

Without that surge suppressor in the coaxial feed, the audio system hums (nastily). In the living room, I have the following equipment:

TV
Cable TV box
Netgear Orbi cable modem/router/wireless access point
Mac mini (running my Roon server) with outboard USB HDD & USB disc CDRW
Yamaha disc player
Whatever audio gear happens to be in house

The Mac mini can connect to the Orbi via WiFi
The TV, however, wants an Ethernet connection to the Orbi to access online content & updates
The Yamaha disc player wants an Ethernet connection to the Orbi for occasional software updates
The Mac mini, the cable TV receiver box, and the Yamaha disc player are all commonly grounded via HDMI at the TV's input box (and here lies the issue).

If I run my incoming cable through my surge suppressor, it gets grounded to the house ground (and I have no hum). But the Cox guy says "don't do that" (but didn't say why, and I neglected to ask him at the time) It does me no good to split the coax upstream of the splitter & then run only the cable modem part through the surge suppressor - the Ethernet & HDMI get the different grounds back together downstream & I still get hum.

Currently like this:



Suggestions?

[audiobill]

A classic cure is to get two of these, connect "antenna" leads back to back and you have a coax isolation transformer .

www.amazon.com/Fancasee-Matching-Transformer-Converter-Connector/dp/B07BW9YS4Q

[creimes]

Where the coax feed comes into the house, is it grounded ??

[405x5]

May 31, 2022 22:44:39 GMT -5 creimes said:

Where the coax feed comes into the house, is it grounded ??

Exactly….a proper earth ground there is key.
Sometimes it’s a good investment to have a licensed electrician review and test a residential service to correct such issues. This is an electrical problem now, not a cable issue (from what I read).

[housetech]

We have AT&T cable internet service with ability to use Voice over Internet Protocol (VoIP) phone service from an all-in-one unit and no coax splitters before the modem. Call Cox and ask if they have an all-in-one cable modem with VoIP to eliminate the splitters.
Everything worked fine when we used VoIP. Remember, your original phone service (Ma Bell) and all that wiring is no longer being used, maybe disconnecting Ma Bell wiring going into the house would help.
Lastly, you are probably on different electrical circuits (guessing)- one AC circuit for the cable modem & router and your Audio on another circuit in another room. That can cause a potential difference due to a loose/corroded ground either on a AC wall plugs or at the breaker box.
Install you surge suppressor, between Splitter 2 & cable box and see what happens.
Somewhere you have a grounding problem, maybe coax wiring- try replacing the coax cables one at a time with a known good RG6.

btw, what was the time between the 1st service and last service?

[Boomzilla]

May 31, 2022 22:44:39 GMT -5 creimes said:

Where the coax feed comes into the house, is it grounded ??

I strongly doubt it. The cable ground seems to be at a different potential than the house ground. And therein lies the problem. If I run the coax through a surge-suppressor box, the box grounds the cable ground to the house ground (and all hum disappears). Unless the surge suppressor is in the coax path, though, EVERYTHING hums.

[Boomzilla]

Jun 1, 2022 11:16:08 GMT -5 housetech said:

We have AT&T cable internet service with ability to use Voice over Internet Protocol (VoIP) phone service from an all-in-one unit and no coax splitters before the modem. Call Cox and ask if they have an all-in-one cable modem with VoIP to eliminate the splitters.
Everything worked fine when we used VoIP. Remember, your original phone service (Ma Bell) and all that wiring is no longer being used, maybe disconnecting Ma Bell wiring going into the house would help.
Lastly, you are probably on different electrical circuits (guessing)- one AC circuit for the cable modem & router and your Audio on another circuit in another room. That can cause a potential difference due to a loose/corroded ground either on a AC wall plugs or at the breaker box.
Install you surge suppressor, between Splitter 2 & cable box and see what happens.
Somewhere you have a grounding problem, maybe coax wiring- try replacing the coax cables one at a time with a known good RG6.

btw, what was the time between the 1st service and last service?

The AT&T phone wiring is disconnected from everything. Cox telephone service (that I do have) IS a VoIP service. We don't much use the house phone, but since it came in a Cox bundle, it cost virtually nothing to add it.

In fact, EVERYTHING I showed in the diagram is on the same living room AC circuit, so no issues there. The ground issue is DEFINITELY between the house wiring and the cable coax. I'll just have to undo what the cable guy did and put my surge suppressor back in the path. Since it affects the ground and not the signal wire, it should have no effect on the signal strength.

Thanks!

[ttocs]

I'd be interested to know what the voltage potential is before you put it back the way it was.

[Boomzilla]

Jun 1, 2022 17:38:37 GMT -5 ttocs said:

I'd be interested to know what the voltage potential is before you put it back the way it was.

I’ll measure it.

[Boomzilla]

There is a 0.3VAC difference between the house ground and the cable company ground. This is enough to prevent the subwoofer from sleeping. The sub produces 10-15dB hum @ 60 Hz. when the cable system is ungrounded to the house ground.

[KeithL]

"Ground" is actually not as specific a thing as you may think.
They probably use "Earth ground" rather than "power line ground".

(Usually the transformer is grounded at the pole; the cable is grounded at the house; and the two are connected through the power drop.)

But the "cable ground" should be the same as, or VERY close to, the "house ground".

The cable is SUPPOSED to be "properly grounded"... both for the obvious reasons and for safety reasons.

That MAY be within what they consider acceptable...

But it could also mean that one of the ground connections is broken or loose...

(Cable grounds often get damaged or simply work their way loose.)

So I would get the cable company to come in and look at it...

[KeithL]

Just FYI... a surge suppressor that protects something from input surges MUST be connected to the signal line in some way.

About the least intrusive is a gas-breakdown type device... but even they have some slight capacitance.

So it may still have at least some slight effect on signal strength.

Incidentally:

1. Since coax cable itself has significant losses over distance copper-based cable systems are designed to tolerate a rather wide range of signal levels without problems.

    The cable installer will usually actually put a meter on the line and confirm adequate signal strength at the box.

2. An isolation transformer (coax) will have some insertion loss... but it won't be too bad with a good one.

3. Splitters actually split the power between multiple lines... and are also somewhat lossy... so a two-way splitter delivers bit less than HALF of the original level to each output.

4. HOWEVER, not all splitters are equal, and some will not properly pass the entire range of frequencies required by the cable company signal.

    It's not a matter of price... some cheap splitters will work just fine... but not all of them.

5. Current cable systems also require TWO-WAY communication between the box and the system...

    Therefore any splitter you add must also act as a "combiner" in the upstream direction...

    This makes it a little more particular about what splitter you use... and how many... and where.

    And things like "powered distribution amplifiers" probably won't work at all.

    (And some splitters don't do well at all at passing upstream signals.)

6. ALL coax connections SHOULD be properly terminated (even though most modern systems are quite tolerant if you break this rule).

I don't know about Cox... and it probably varies by area...

But most cable companies I know use two boxes... one for cable TV ("the cable box")  and one for Internet and voice ("the cable modem")...

With one line coming in... and one splitter to feed both from it...

Also note that some power strips include a COMBINED "coax surge protector and splitter"... with one input and multiple outputs...

These WILL cause a significant loss in signal going to each output... for example, if you have four outputs, each will receive less than 1/4 of the incoming signal...

(And this will be true even if you're only using one of those four outputs.)

In addition, ANY UNUSED OUTPUTS ON ANY SPLITTER, will by definition not be properly terminated.

This has the potential to thoroughly bugger up the signal at the frequencies being used (a coax cable is supposed to be properly terminated.)

Likewise ALL coax cable that "has live signal on it" loads down the signal and reduces its strength.

It's NOT like power circuits... where unused outlets "don't count".

MOST systems tolerate this but it is a good first place to look.

For example, when I moved into my home, there were "cable outlets" in several rooms... being fed by a splitter in the incoming junction box...

Since I was only planning to use the connection in one room the first thing I did was to bypass the splitter with a "bullet" - feeding only the connection I'm using.

This eliminated both the extra load from all that extra cable and the un-terminated connections at the end of each branch.

(This has a way of getting worse over time... for example if you add a splitter inside the house and forget that you're already going through one in the junction box.)

None of these is individually "a deal breaker" with modern cable systems...

But they are all potential culprits when something doesn't work as well as it should...

Jun 1, 2022 15:54:12 GMT -5 Boomzilla said:

Jun 1, 2022 11:16:08 GMT -5 housetech said:

We have AT&T cable internet service with ability to use Voice over Internet Protocol (VoIP) phone service from an all-in-one unit and no coax splitters before the modem. Call Cox and ask if they have an all-in-one cable modem with VoIP to eliminate the splitters.
Everything worked fine when we used VoIP. Remember, your original phone service (Ma Bell) and all that wiring is no longer being used, maybe disconnecting Ma Bell wiring going into the house would help.
Lastly, you are probably on different electrical circuits (guessing)- one AC circuit for the cable modem & router and your Audio on another circuit in another room. That can cause a potential difference due to a loose/corroded ground either on a AC wall plugs or at the breaker box.
Install you surge suppressor, between Splitter 2 & cable box and see what happens.
Somewhere you have a grounding problem, maybe coax wiring- try replacing the coax cables one at a time with a known good RG6.

btw, what was the time between the 1st service and last service?

The AT&T phone wiring is disconnected from everything. Cox telephone service (that I do have) IS a VoIP service. We don't much use the house phone, but since it came in a Cox bundle, it cost virtually nothing to add it.

In fact, EVERYTHING I showed in the diagram is on the same living room AC circuit, so no issues there. The ground issue is DEFINITELY between the house wiring and the cable coax. I'll just have to undo what the cable guy did and put my surge suppressor back in the path. Since it affects the ground and not the signal wire, it should have no effect on the signal strength.

Thanks!

[Boomzilla]

So this evening, I inserted the surge suppressor in the location noted in the OP, and INSTANTLY the hum is gone. I guess 0.3 volts of ground differential isn't trivial...