Repairing Coaxial Cable - A Difficult Task? 13

[muthabored]

I'd been having trouble with my high speed internet (the connection would suddenly drop on its own for what appeared to be no reason). After speaking with my ISP's tech support, my attention was directed to the coaxial cable that comes in from the outside (the cable is frayed). They offered to send someone out to take a look at it/repair it but I'm wondering if this is something that I could do on my own. I have spare cable and I think I'd have to get one of those connectors (F81) and then something to cut/crimp the cable. Can anyone refer me to a website that might assist me with this? Thanks in advance!

 

[vacunita]

Unlike rj45 cat5 Ethernet cables, coaxial cables are single line. cutting out the affected section and adding terminators to the ends is all there is to it. Of course the crimping tool is required.

A good Crimping tool should be able to peel the cable and crimp in the "terminators";


----------------------------------
Ignorance is not necessarily Bliss, case in point:
Unknown has caused an Unknown Error on Unknown and must be shutdown to prevent damage to Unknown.

 

[gbaughma]

Let them repair it.

If the cable is outside, you will spend much more on getting the proper connectors and compression fitting tool.

High-speed coax should *NEVER* be crimped, stapled, bent, etc. It's not just about the center conductor and braiding; it's about the dialectric (the foamy center around the center conductor). Contrary to popular belief, *that* is where the signal is transmitted.

The cable needs to be terminated with a compression fitting, which doesn't crimp the dialectric; and since it is an outside connection, it needs to be water-tight and so forth.



Just my 2¢

"What the captain doesn't realize is that we've secretly exchanged his dilithium crystals for new Folger's Crystals." -- My Sister
--Greg

http://parallel.tzo.com

 

[wahnula]

it's about the dialectric (the foamy center around the center conductor). Contrary to popular belief, *that* is where the signal is transmitted.

Whoa! News to me and great to know.

I also would let the cable company do it. I had an intermittent cable connection and it turned out to be the splitter at the PC. No splitters for me! When I built my new home I allowed for a dedicated cable for broadband and another for video.

 

[ArizonaGeek]

I'd say let the cable co. repair it as well, and if you stand there and watch them make sure they don't just splice together the two pieces make sure they run a new cable. My wife used to work for Cox Cable (very briefly, she hated it) and they used to charge $45 to run a new cable. I know someone that runs cables for a living (he does high end houses and business) and he said he wouldn't even show up for $45.

Just a crimper to do it yourself would cost you $35 to $40 for a decent one. Like gbaughma said you'll only wind up with other problems down the line if you do it yourself.

Cheers
Rob

 

[LawnBoy]

Contrary to popular belief, *that* is where the signal is transmitted.

Care to back up that assertion? Electrons don't flow in a dielectric, by definition. The shape of that dielectric is critical to maintaining the capacitive impedance of the cable, and the higher the frequency the more critical that shape becomes, but a signal will not flow through an insulator...

You may be talking about 'skin-effect' where the signal travels on the outside of the conductor, but it still travels on the conductor, not it's insulator.

 

[gbaughma]

Lawnboy:

Of course I'll back it up.

I'm SBCA certified, and in class we were not only taught, but *shown*, that a crimped dielectric will cause notching of signals at higher frequencies. That is why RG-59 is only good for standard "broadcast" frequencies, and that is why RG-6 (with a thicker dielectric) is used for digital signals up to the 5GHz range.

I've seen what a crimped dielectric will do on an o-scope. You can see the frequencies notch right off by several DB.

That is also why, when I was taught how to properly terminate with non-crimping compression fittings on RG6, that it was imperitive that the Dielectric be in the proper position as well, so that it will in fact come in contact with the grounding barrel or device that it is connecting to. I have seen the difference, once again on an o-scope, that an improperly terminated connector will make.



Just my 2¢

"What the captain doesn't realize is that we've secretly exchanged his dilithium crystals for new Folger's Crystals." -- My Sister
--Greg

http://parallel.tzo.com

 

[gbaughma]

Lawnboy:

Oh... and just a follow-up... signal, in the case of RF, isn't electrons.

If it were, you couldn't walk by a transmitter without being electrocuted.

(I'm also a HAM operator... hehe... we're licensed to run up to 1500 watts legally...



Just my 2¢

"What the captain doesn't realize is that we've secretly exchanged his dilithium crystals for new Folger's Crystals." -- My Sister
--Greg

http://parallel.tzo.com

 

[muthabored]

Thanks to all who replied.

 

[edfair]

How about backing it up some more, Greg.

Sure, crimped cables will cause a signal failure. But somewhere there is a book that explains that the signal is transmitted by the diletric if that is the case.



Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[LawnBoy]

You can see the frequencies notch right off by several DB.

Yep, that's because you changed the shape of the dielectric, thereby changing the cable's impedance.

Oh... and just a follow-up... signal, in the case of RF, isn't electrons.
If it were, you couldn't walk by a transmitter without being electrocuted.

You're confused. Any signal conducted by a wire is propagated by electrons. You said it yourself, you're liscensed to run 1500 watts. Watts = current times voltage (P=IE). That current is then converted to electromagnetic radiation by the antenna. Once the signal leaves the antenna there are no electrons involved, but on the wire there most certainly are.

From the Merriam-Webster online dictionary: conductor - d (1) : a material or object that permits an electric current to flow easily.

Current is comprised of electron flow.

And a compression fitting is a crimp-on fitting. The connectors are formed in such a way as to prevent the dielectric from becoming distorted.

I'm not a HAM but I have played one on TV. (I've also had jobs building cell sites).

 

[wahnula]

So now I am confused. Is it is or is it ain't (cable Internet signal) conducted by the dilectric??? To someone with no electronic training except building lots of Heathkits as a kid (me), the foam as an insulator and encapsulator makes sense...as does reducing the distance between the conductor & ground by cripming being damaging to proper conduction. But foam as a conductor of signal? Sounds counterintuitive to me, which is why I ask for a definitive answer. You guys are gods!

Tony

 

[edfair]

If it was a conductor you would have a short. Nothing would get through to the other end. If it was a partial conductor the signal getting through would be different depending on how long the cable was.

What you have is a high quality capacitor that generally doesn't pass current at the frequency used. But changes to the capacitor cause it to pass some frequencies at the point where the dilectric is damaged. Suspect that this sets up standing waves that causes other interference, but my RF theory was 50 years in the past and the memory has been purged a time or two.

In the second post it was stated that terminators were added to the ends. Should have been terminations. Terminators generally refer to loading resistors used to match impedance between devices or to insure that there is a load to eliminate standing waves.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[LawnBoy]

What you have is a high quality capacitor that generally doesn't pass current at the frequency used. But changes to the capacitor cause it to pass some frequencies at the point where the dilectric is damaged. Suspect that this sets up standing waves that causes other interference,

An excellent explanation, Ed.

 

[gbaughma]

<Sigh>

According to Encyclopedia Britannica:

coaxial cable

Self-shielded cable used for transmission of communications signals, such as those for television, telephone, or computer networks. A coaxial cable consists of two conductors laid concentrically along the same axis. One conducting wire is surrounded by a dielectric insulator, which is in turn surrounded by the other, outer conductor, producing an electrically shielded transmission circuit. The whole cable is wrapped in a protective plastic sheathing. The signal propagates within the dielectric insulator, while the associated current flow is restricted to adjacent surfaces of the inner and outer conductors. As a result, coaxial cable has very low radiation losses and low susceptibility to external interference.



Just my 2¢

"What the captain doesn't realize is that we've secretly exchanged his dilithium crystals for new Folger's Crystals." -- My Sister
--Greg

http://parallel.tzo.com

 

[LawnBoy]

The signal propagates within the dielectric insulator, while the associated current flow is restricted to adjacent surfaces of the inner and outer conductors

I think we're arguing semantics. This explanation confuses me (and once upon a time I had a 2nd class FCC license). How can a signal on a wire have an 'associated' current flow? The signal is the current flow, they are the same thing. Look at waveguides, there is no dielectric... (in the ones I've worked with, anyway).

If you can come up with an authoritative technical reference ( I don't consider an Encyclopedia to be a technical reference) stating this, I'll concede the argument.

 

[diogenes10]

I always thought Britannica was pretty authoritative.

I am very poor at understanding technical electric stuff, but that explanation kind of makes sense to me. There is a piece of electricity running along through a wire pulling a message along through material surrounding its wire. Then there is another piece of electricity guarding the inner piece of electricity and its piggyback message rather like the warp shields on the Enterprise.

Also, conceptually, is it possible that insulator is the wrong word here and the the more proper word - to follow the concepts of how this kind of wire works - would be separator or spacer?

 

[gbaughma]

Actually, if you think about it, that's the reason that RG6 is used in satellite, instead of RG59.

Electrically, they're the same, however the size of the dielectric makes the difference. The RG59 doesn't have enough bandwidth, whereas the RG6 does. (this was also covered in my SBCA certification).

If it was just a matter of signal and current and so forth, lamp cord would work just fine for all of it. If it was just a matter of getting electricity.

I realize the issue here is that folks are thinking a digital signal (such as cat-5), where "pulses" represent ones and zeros and are decoded at the other end. But in this case, you're dealing with an analog radio signal.

The dielectric acts as a waveguide, propagated down to the other end. The way it was explained to me is that the lower frequencies are propagated more towards the center, whereas higher frequencies are more towards the outside, nearer the sheilding. When you crimp a dielectric, by stapling it or whatever, you're essentially "pinching off" those frequencies travelling down that portion of the dielectric. As I said, I've actually seen this on a frequency analyzer; we did it in class.

In a satellite dish, the voltage down the cable actually powers the LNB. On your cable television coming into the house, that voltage is only 1 v p2p (Peak to peak).

I built a ham radio antenna (stacked j-pole, if anyone cares) out of rigid copper pipe. I asked one of the other ham operators, as I was stripping the wire and attaching it to the copper pipe, why this even worked.... I mean, why didn't it dead short and blow up my radio, especially when I started pumping voltage into it.

The way that it was explained to me is that an antenna's job is to be "lossy". The voltage goes down the wire, and is converted to radio signals by the impedence of the antenna. I don't pretend to understand all of it, but essentially the power "squirts out the end" of the antenna, when the power is converted to radio signals (based on the frequency of the power being pushed).

More information about how antennas work can be found at

http://electronics.howstuffworks.com/question490.htm

Just my 2¢

"What the captain doesn't realize is that we've secretly exchanged his dilithium crystals for new Folger's Crystals." -- My Sister
--Greg

http://parallel.tzo.com

 

[LawnBoy]

First I'd like to say that I respect Greg's opinion, I've seen him offer excellent information in this and many other forums. It's entirely possible that I am not understanding the issue clearly, so I continue the debate.

I agree that higher frequencies change things so that lamp cord no longer works well over distance.

Electrically, RG6 and RG59 are not the same. RG6 has a beefier center conductor and usually has much better shielding, resulting in a larger dielectric to maintain 75 ohms impedance. Think of a capacitor, if you increase the size of the plates you must increase the spacing between them to maintain the same capacitance.

The design of antennas is well outside my expertise and I'll take your word for how they work. I really only understand dipoles.

To be honest, I have heard before what you are saying about the coax acting as a waveguide. It was presented as a thought-experiment to help get a grip on the practical aspects of cabling. It was not presented as scientific fact. If it is scientific fact, it should be stated as such in a technical reference somwhere. Does anybody have such a reference that has been peer reviewed?

 

[gbaughma]

Well, other than the reference to it in Britannica, and what I was taught, and actually shown, in class, I don't have anything at the tip of my fingers.

I was surprised to find out in my class the information about the dielectric as well, and even questioned it, until I was shown on the scope.

The difference is, when you're talking television/cable modem/etc. you're essentially using the coax as a waveguide. When you're transmitting, you're moving power at a certain frequency, which is then being converted by the antenna to radio radiation.

It's really an apples and oranges thing.... I'll see what other information I can find. Or perhaps an elmer on here would like to chime in...

73
KC0KRB



Just my 2¢

"What the captain doesn't realize is that we've secretly exchanged his dilithium crystals for new Folger's Crystals." -- My Sister
--Greg

http://parallel.tzo.com