Entertainment Center: TVs, Stereos, VCRs and DVDs - Big fat TV cable

I didn’t know if I should have posted to the computer forum or here.

My TV cable runs underground from a box at the curbside to my home. Due to a failed underground splice, it was replaced. The replacement cable’s diameter is 3/4inches in diameter (OD). It is Commscope type P111 1000 Jacass, and has a large copper clad inner conductor of about 10 or 12 gauge, surrounded by 1/8 inch of insulation, enclosed in a flexible aluminum tube. Around the tube is a self-sealing compound, another aluminum tube and the outer plastic casing. It has a bending radius of about 10inches.

I have DSL for my three PC’s but will switch to a cable modem next Tuesday. I want to replace my in-house RG6 wiring with a straight shot of about 60feet to where the cable modem will reside next to my router. At that point, I will use a 3ghz splitter to service the TV’s and the modem. Presently I have splitters all over the place.

The cable company did a good job running the cable to my house, but a terrible job connecting to my home including securing it to the power meter mast. It also bows out about 2feet from the house because of its rigidity. I plan to cut about 2feet off the cable and make my connections in a weatherproof box. To do so means I have to redo the connector on the Commscope cable.

Finally here’s the question, sorry for the long lead-in. I don’t know what type of connector it is, if it can be re-used, and if I need a special tool. I have a very good selection of DYI tools. Should it be connected to the grounding rod? Thanks in advance.

If it's not coax, how and where does it connect to the coax in your house?

Since I posted, I decided to remove the connector. Removing it and reinstalling it was easily done though I had to fabricate a tool to remove some of the inner insulation. The connector terminated in the standard RG6 connector.

The cable was not a coax, I would call it a triax cable consisting of the central conductor and the outer and inner aluminum tubes (shields). The outer tube was not electrically connected on the house side, I don’t know about the other end.

I’m all wired and set to go, just waiting for the cable guy to bring the new modem.

Thanks

1Geniere - I would use compression fittings for the cable, they are far superior than the crimp type ( the more pressure you put on the cable the greater the loss of signal. ) ...
Can't reuse compression fittings.
Best tool is Ripleys Compression tool

The parts of a Cable include:

1 Outer Shield - protects, weatherproofs

2. Braid & Foil - Grounds it

3 - Dielectic - Carries the signal ( lots of people think this is insulation, but it isnt. )

4. Center Conductor - Carries the DC Volts ( copper wire in middle )

Be sure to Ground the cable to your common Ground line at your Power box with min. #10 Green or #8 Aluminum.

Hope this helps

ROB

Thanks Rob:

The connector supplied by the cable company was a compression type and acted against the inner aluminum tube slightly deforming it outward when tightened (bulged out). I thought it to be a clever design and it seems it could be used over and over. Unlike a plumbing fitting, it used an integral (non-removable) split ring so it does not seal completely. I will have to weatherproof it. The provided cable did not have “braid and foil” but used the inner aluminum tube for the purpose. The link to the Commscope site (below) shows the cable (second picture from top).

Indeed the center conductor is embedded in a dielectric, a poor charge conductor but is permeable to EM fields.

Grounding it is a little problematic, as it seems I’ll need to use two grounding wires to connect to the earthed rod. One wire for the connector body and another for the outer aluminum tube.


http://www.commscope.com/html/db_trunk.shtml

Just make sure the ground rod is at least 8 ft and 5/16" diameter MIN.

Hope all works great for you!

ROB

The metal shielding provides your return path to the cable company. Unless you run is more than 250ft i'd be curious to why they ran RG11 to your house.

It is called RG11 and you can find all the tools at BudCo Cable. Look it up in google if you are so inclined. I would not suggest doing this yourself. I was a cable guy for a while and when it comes to cable modems the stuff is touchy.

However, your 3 Ghz splitter rating is worthless. 1000hz is the fastest any signal for analog television goes anyway and that is the rating the cable company uses (and for good reason, even though they seem incompetent they actually do know how to cable) Those extra ratings are just another way to make you pick it over a cheaper model and pay more for nothing.

Anyhow, I would guess that the cable company would actually not be happy if you were messing with their RG11. RG59 or RG6 they couldn't care less about, but the 11 is some expensive stuff. What they should have done is not left a drip loop on the incomming line and stopped it before it turned into the house. (I cannot imagine anyone running RG11 inside the house even if only to a centralized cable circuit). Basically, put a short piece sticking out fo the ground, using a grounding connector, and running RG6 off of it back to the inside of the house.

Also, running the ground off of the power mast is standard procedure and accepted under code. It isn't the most graceful of approaches but it does work and is technically acceptable (and common practice).

Have fun!

1Geniere - I would use compression fittings for the cable, they are far superior than the crimp type ( the more pressure you put on the cable the greater the loss of signal. ) ...
Can't reuse compression fittings.
Best tool is Ripleys Compression tool

The parts of a Cable include:

1 Outer Shield - protects, weatherproofs

2. Braid & Foil - Grounds it

3 - Dielectic - Carries the signal ( lots of people think this is insulation, but it isnt. )

4. Center Conductor - Carries the DC Volts ( copper wire in middle )

ROB

I know this has nothing to do with the OP question. But I wanted to throw out what I had heard about Coax signals because it doesn't line up with what has been said here. I could be wrong, but if that is the case I would like to learn the truth.

"Dielectric" literally means, not conductive (or insulation). The center conductor is considered to carry the signal, both DC (rare, but possible) and AC. In all actuality, the signal really is the difference between the center conductor and the outer metal-braided shield(s). Since the outer shield is usually grounded (referenced at 0Volts) the signal is only considered to be carried on the center conductor. My cable company grounded the shield of the coax to my housing's ground, I believe the is required by the NEC codebook.

The better the dielectric material is, the better the signal will be because there will be less signal loss. If a dielectric lets NO signal pass between the conductors, the cable could span miles with no signal loss. No perfect dielectric exists though. Also, outside factors can alter the signal such as power lines or any other strong signals. The outer metal shield "blocks" those signals (interference) from reaching the center conductor. RG11 has two outer shields(I believe that both of them are grounded, but I'm not certain), so it has two layers that block any interference. This along with its thick center conductor allows it to have very little signal loss.

Anyway, thats what I know about coax. I've been wrong before.

The shielding has multiple functions. I was a cable guy for some time during college so I know how the system works (in my area at least but I think it is safe to assume it is universal considering I have come into contact with other proffesionals from other states and have indicated the system is the same).

The dielectric material is the white stuff (I believe pvc or silicon based) around the copper core (sometimes called stinger) of the cable. So you are correct with the statement that the dielectric does NOT send any sort of signal.

The part that is often called the "sheilding" is the braided wire. For lossless transmission RG11 is used to run signals across great spans or to large load destinations (a.k.a apartment complex's, businesses, etc.) because the larger medium can carry the signal farther. This cable is redundant in or to a house that is less than 200ft away from the ped/pole.

Technically, the sheilding (braided wire) is used for the return path (up stream) to the cable company for digital and cable modem services. The central core is not bi-directional. If you still don't believe me, go cut open your wire, and break continuity of your briaded wire (physically sever it leaving only the copper continuous) and restart your cable modem. You'll never get upstream untill the braided wire connection is reestablished.

Guys,
I also agree with kuhurdler's description re dielectric.

Skyking;
you may be correct with the center core of coax re cable service, but it is bi-directional in a satellite system. The digital signal comes down from the dish/lnbf to the receiver and current (12 to 20 volts) is sent by the receiver to the lnbf to change polarity/satellites.

fred

Good point.

Technically, the sheilding (braided wire) is used for the return path (up stream) to the cable company for digital and cable modem services. The central core is not bi-directional. If you still don't believe me, go cut open your wire, and break continuity of your briaded wire (physically sever it leaving only the copper continuous) and restart your cable modem. You'll never get upstream untill the braided wire connection is reestablished.

I agree with you mostly. But the reason your cable modem won't establish upstream (and probably not downstream either) is this:

"In all actuality, the signal really is the difference between the center conductor and the outer metal-braided shield(s). Since the outer shield is usually grounded (referenced at 0Volts) the signal is only considered to be carried on the center conductor."

The upstream signal does travel on the center conductor. Your cable modem chooses an un-used frequency when it turns on. It then uses this frequency to broadcast your "upstream" signal back to the cable companies equipment. The reason it couldn't be broadcast on your shield (braided wire) is that there are numerous places where this is grounded. That upstream signal would be eliminated (or at least very drained) everywhere that cable is grounded.

Here is the frequencies from my cable modem's status page:
Downstream:
Frequency 711000000 Hz
Upstream:
Channel ID 3 Frequency 23984000 Hz


However, to expand on your theory about disconnecting the ground at your cable modem: If you grounded the shield of the coax cable, and then grounded the shielding at your cable modem so that only the center conductor was running between them, it WOULD establish an upstream and downstream connection (if your grounds were actually the same voltage). It would also be very noisy because the center conductor would not be shielded anymore, and those "grounds" would have to be identical.



Technically, its more complicated than this, and you're partially right because no cable system could operate without the shielding of the coax (since it is a common reference). So I guess you could consider that shielding necessary to carry the signal, since it couldn't operate without it. Uggh, my brain hurts now from thinking about this. In simplified terms though, the shield is grounded, and the signal is transmitted on both ends over the center conductor.

"Technically, the sheilding (braided wire) is used for the return path (up stream) to the cable company for digital and cable modem services."

Whaaaa?

Never heard so much rubbish in all my 25 years as a radio technician!

Simply put, a co-axial cable (ANY co-axial cable) is an unbalanced transmission line. It's purpose is to transfer signal from source to load with as low a loss as possible, so that all (or close to all) of the signal is dissipated in the load. To achieve this, the cable is selected to have a characteristic impedance (Zo) equal to the source and load impedance. In a duplex system (2 way communication), the cable acts in exactly the same way in both directions (the source becomes the load and vice versa). If the load (eg your PC) was truly isolated from ground and you then cut the outer conductor (the braid), you would totally lose communications BOTH WAYS!

Please don't spread such uninformed heresy again!