What is the theory behind Category 5 cabling?

[Fiona 0]

Cat 5 cable consists of 4 pairs of 24 AWG wire which is preferably stranded copper. Each of the 4 pairs are twisted to increase the current carrying capacity. And the twists vary in number to avoid ‘crosstalk’ between each pair. The impedance is rated at 100 ohms, though individual 24 AWG wires seem to be rated at 76 ohms which is close enough to the RG59’s 75 ohm impedance rating. The practical limit in length for CCTV applications is about 300’ as opposed to the RG59’s which is 750’.

 

Question: The RG59 was originally a military specification cable. It is so massively overbuilt in comparison to a Cat 5 - and yet this marginally constructed Cat 5 is capable of conducting a video signal over lengths long enough for most installations. What is the theory that explains the capability behind an insubstantial 24AWG pair (100Ω) to carry a signal that was once the domain of RG59 and RG6? What happened to the 95% copper shielding and the dielectric core? The SCC is about 6mm in diameter and the signal travels along the outer microns; and this was replaced by about ½ mm diameter 24AWG. Any explanations?

Edited January 16, 2012 by Guest

[PaulsonLaw 0]

Now I just got my system online this week....

 

I have a 385 run of "tough cable" the cat 5 TC-L2...

 

This run has 4 bullet cams each on a pair, no splices all the way to the dvr & I have no problem at all....

 

The company tech claimed they can run 1200' on the TC-L2....

 

So there are options over the UTP cat5 300' limit....

[Fiona 0]

Cat 5 TC-L2 uses 22AWG and the specs claim additional shielding at Cat 6.

 

See: http://www.wisp.net.au/pdf_datasheet.php?products_id=429

 

This is still very close to the original Cat 5 specifications.

 

The TC-L2 uses 22AWG with a .065 mm diameter yet it achieves four times the signal conducting distance of 24AWG.

[Soundy 1]

Cat 5 cable consists of 4 pairs of 24 AWG wire which is preferably stranded copper. Each of the 4 pairs are twisted to increase the current carrying capacity.

Incorrect. Twisting the wires has no effect on the current capacity - in fact, if anything it would reduce the overall usable length as the ACTUAL length of the copper is longer than the twisted length. The wires are twisted to aid in rejecting EMI.

 

And the twists vary in number to avoid ‘crosstalk’ between each pair.

Right.

 

The impedance is rated at 100 ohms, though individual 24 AWG wires seem to be rated at 76 ohms which is close enough to the RG59’s 75 ohm impedance rating.

It's rated *nominally* at 100 ohms *at 100MHz*. Impedance will vary depending on the actual frequency(ies).

 

The practical limit in length for CCTV applications is about 300’ as opposed to the RG59’s which is 750’.

VERY wrong. 100m/330'. is the limitation of the *ethernet* spec over UTP (Cat5/5e/6). Composite video (whether CCTV or otherwise) can be run anywhere from 1000' to 3000' using passive baluns (depending on what manufacturers' claims you believe - one particular GEM model I just looked up claims "Max Distance: Color: Cat3 - 1200ft, Cat5 - 2200ft; Monochrome: Cat3 1500ft, Cat5 2500ft". Using active baluns at one or both ends can extend that to over a mile. (Other types of networking, BTW, do not run into the 300' limit either - we used to run token-ring over Cat3 for over 500'.)

 

Question: The RG59 was originally a military specification cable. It is so massively overbuilt in comparison to a Cat 5 - and yet this marginally constructed Cat 5 is capable of conducting a video signal over lengths long enough for most installations. What is the theory that explains the capability behind an insubstantial 24AWG pair (100Ω) to carry a signal that was once the domain of RG59 and RG6? What happened to the 95% copper shielding and the dielectric core? The SCC is about 6mm in diameter and the signal travels along the outer microns; and this was replaced by about ½ mm diameter 24AWG. Any explanations?

It has absolutely NOTHING to do with the wire size, and specifically to do with use of baluns (short for BALanced/UNbalanced) to create a balanced line, which provides greater noise rejection.

 

Also, DC resistance is not the enemy of long-run signals, capacitance is: capacitance in a cable has the same effect as placing a capacitor across the wire, which creates a low-pass filter effect, rounding off the higher frequencies. The higher the capacitance, the lower the cutoff frequency, and the more impedance it introduces at a given frequency. Cat5e is rated at a nominal 52pF/m, while RG-59 is rated at 68pf/m.

 

BTW, Wikipedia notes that "The 'RG' unit indicator is no longer part of the JETDS system (MIL-STD-196E) and cable sold today under the RG-59 label does not necessarily meet military specifications," so the fact that "RG59 was originally a military specification cable" isn't really relevant.

[Fiona 0]

You seem to be emphasizing the point I was making. If Cat 5 can run 2200', what was the point of using RG59?

 

What is it about the design of Cat 5 that allows such high returns for comparitively small amounts of material?

[Fiona 0]

Soundy, so you're saying that the baluns are the key component to the Cat 5?

 

In other words, any length of 24AWG (100s of feet for example) would be capable of conducting the signal provided baluns were used?

[Soundy 1]

The current involved in these types of signals is so low, wire size is really NOT an issue AT ALL. The losses due to capacitive attenuation are far greater than what you'd see from wire resistance itself. Induced noise becomes more of an issue at greater distances, which is part of what a balanced line helps to combat.

 

In other words, any length of 24AWG (100s of feet for example) would be capable of conducting the signal provided baluns were used?

 

I believe that was already covered: "one particular GEM model I just looked up claims 'Max Distance: Color: Cat3 - 1200ft, Cat5 - 2200ft; Monochrome: Cat3 1500ft, Cat5 2500ft'"

 

If Cat 5 can run 2200', what was the point of using RG59?

That's a good question. Some guys still use it because they "don't trust" baluns. Some use it just out of habit. Personally, I almost never use it for new installs.

 

What is it about the design of Cat 5 that allows such high returns for comparitively small amounts of material?

Nothing - the magic is in the balanced line. Baluns work almost as well over any type of UTP, and even over simple un-twisted pairs such as station wire, speaker wire, etc.

[Fiona 0]

Perhaps this was already mentioned, and I just missed it:

 

Why was RG59 used for the last umpteen decades if simple 24AWG would have sufficed?

 

In the Age of Ecology, think of the difference in copper consumption between the two types, not to mention the increased consumption of oil-dependent plastics.

[rory 0]

If Cat 5 can run 2200', what was the point of using RG59?

at $50 for a pair of baluns, that increases the cost of the install greatly.

[tomcctv 190]

Soundy, so you're saying that the baluns are the key component to the Cat 5?

 

In other words, any length of 24AWG (100s of feet for example) would be capable of conducting the signal provided baluns were used?

 

 

 

cat5/ alarm cable or bell wire are balanced cables use of a balun will unbalance so yes will work.

 

 

Why was RG59 used for the last umpteen decades if simple 24AWG would have sufficed?

 

 

baluns had not been invented then (thats the only reason)

 

coax was and is still needed but made the way it is to stop cross talk between center pin and sheild. any signal down coax has voltage (not camera power) this is unbalanced signal

 

 

cat5 is the same but balanced cable (the voltage being the signal) this is why if you dont use baluns at each end you infact have a dirty signal lines on screen. adding baluns unbalance the signal

[Fiona 0]

Thank you Soundy, Rory and Tom for the technical explanations.

 

I don't want to wear the Integrators out, so I will do some individual research on the phenomenon of unbalanced vs. balanced signals and how the balun affects the later.

[trythis 0]

Learning a lot here, thanks.

 

I now feel kinds dumb for buying siamese coax.

[rory 0]

Learning a lot here, thanks.

 

I now feel kinds dumb for buying siamese coax.

Im doing a quote right now that involves 10,000' of RG59 siamese.

Mostly short runs and completely separate buildings/locations.

You use what you have to. Although for one building it may be all cat5 as it should work out to be the same price or even cheaper due to the amount of runs, and easier to run when its that many cables (lighter cable, siamese wears your body down).

[tomcctv 190]

Learning a lot here, thanks.

 

I now feel kinds dumb for buying siamese coax.

 

 

 

its just down to how you plan a system. nothing wrong with using coax I.E if you just have 4 cameras and your wirering is like spider (this way that way) then coax or cat5 can be used coax is cheaper as your only cost is BNC but if you have cameras all located down far end of a building cat5 is better no need to run 4 coax so you save costs and you also save costs in install time.

 

cat5 is also future prof. later change from analog to ip ..... and it also gives you more scop if you want to add audio or data

[Numb-nuts 1]

did anyone see Coronation Street this evening?

[Soundy 1]

If Cat 5 can run 2200', what was the point of using RG59?

at $50 for a pair of baluns, that increases the cost of the install greatly.

True when baluns were $50/pair. We're using GEM mini-baluns now that run about $5/pr. and from my basic bench testing, work just as well as the $30/ea. Muxlab units I tested as well.

 

I don't want to wear the Integrators out, so I will do some individual research on the phenomenon of unbalanced vs. balanced signals and how the balun affects the later.

Here's a good, very basic description of the difference - it's written about audio (balanced audio lines have been common in live and studio applications for decades, especially for low-level signals like microphones), but the same principals apply.