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Coaxial Cables - Which one (OHMS)?

Papercut

Papercut

Jermaine Jenas
Sorry lads - another question thread! :oops:

Okay, so planning to move my Virgin Media Superhub from one room to another (out of the window and back in - so external for half the length). I'm looking at about 20m in length...

Now where it gets complicated for me... I see that there are different Ohms attached to each cable. I think I understand that 50Ohms is for Ethernet/Internet and 75Ohms is better for Video. Is the right? Would 75Ohms be even better for Ethernet/Internet or do you have to stick to a lower Ohm? Does the fact it will be partially external make a difference?

Anything else to consider?

Both ends will be 'Male' if that makes any difference.

Thanks!
 
Superhub is the modem/router so internet

(High speed - if that makes a difference)

Cheers Arc
 
I found this

http://www.broadbandutopia.com/coaxial.html

RG6 Coaxial Cable

RG6 is the recommended coaxial cable for distributing signals from cable TV, satellite dish or from a roof-top antenna. The RG6 cable construction provides better sheilding than the older RG59 coax cable. RG6 cables that we carry are triple or Quad Shielded. Available in 500 and 1000 foot lengths, Belden RG6 cables also have additional Duobond Plus/Duofoil features that make them the industry leaders.

For video distribution in homes, offices and restaurants we recommend the Belden 7915A and 7916A coaxial cables. Sweep tested to 3.0 GHz, these cables have the UL fire rating and are designed for DBS(DirectTV/Dish etc.), Broadband CATV(digital cable), Cable Modem and HDTV.

For broadcast studio quality DBS/CATV/HDTV distribution in your home/office, we recommend the 4.5 GHz copper braided Belden 1694A. With a 95% Copper braid, double sided, overlapped foil, the shield effectiveness of 1694A exceeds that of quad-shield cable.

RG6 Cable Application Sweep Test Range
RG6 Cable for Cable TV 1 GHz (1000MHz)
High End Low Loss RG6 Cable for DBS/Satellite Dish/HDTV 3.0 GHz (3000MHz)
Broadcast Quality low-loss RG6 Cable for HDTV, home theater and broadcast studios 4.5 GHz (4500MHz)


If you need to use a RG6 cable for multiple applications the cable needs to be sweep tested for the entire range of frequencies.




Or this

http://forums.digitalspy.co.uk/showthread.php?t=811182


Alternatively you can try on AV Forums - possibly the best place for such specialised technical advice.
 
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Many thanks Arc

Still at a loss about the Ohms though. I've looked at Wikipedia: http://en.wikipedia.org/wiki/Coaxial_cable and there is a lot of info there.

I believe Virgin use RG6 (not sure of the Ohms) with a core of 1.0mm (I aussme the bit that goes into the Router's connection). However looking further down I see the RG60 is 1.024mm and the notes state: "Used for high-definition cable TV and high-speed cable Internet."

The Superhub can run at 2.4 and 5ghz and with speeds upto 50mb (which is going to be upgraded to 100mb pretty soon it seems).

Cheers
 
ArcspacE said:
Why don't you just buy a wi-fi router instead and use it for all your devices?
Click to expand...

It's a modem/router but can be used solely as a modem with an additional router. The main reason I want to move it is because it's in the nursery and I want to move it to the living room where the majority of kit uses the internet (I want to hard wire the PS3 in via ethernet). When the baby monitor is on, I switch to 5ghz frequency as it affects the signal at 2.4ghz - so hoping the move will help.

I've also read about Gigabit switches but not idea really what they are.

I think I'm desperate for a project! :D
 
lol

Newer PS3 models have wi-fi, just double check first

A Gigabit switch allows you to plug in your internet connection into a single hub and then 'feed' all your internet devices from there via more ethernet cables. Simply offers you more ethernet connection points similar to a plug-point extension
 
Yep, it has wifi but one of the reasons for the cabling is because of the poor signal to the PS3.

The gigabit switch could be another option but I'd rather move the modem/router to provide a better wifi signal (as I don't want to hardwire everything :D)
 
Well, in that case you can double check on AV Forums for the correct impendance but in my opinion you should be safe with a RG6 75Ohm item.

Good luck
 
Papercut said:
Sorry lads - another question thread! :oops:

Okay, so planning to move my Virgin Media Superhub from one room to another (out of the window and back in - so external for half the length). I'm looking at about 20m in length...

Now where it gets complicated for me... I see that there are different Ohms attached to each cable. I think I understand that 50Ohms is for Ethernet/Internet and 75Ohms is better for Video. Is the right? Would 75Ohms be even better for Ethernet/Internet or do you have to stick to a lower Ohm? Does the fact it will be partially external make a difference?

Anything else to consider?

Both ends will be 'Male' if that makes any difference.

Thanks!
Click to expand...

The two types of cable are usually the difference between TV type applications and radio.

The impedance of the cable - the figure in Ohms is matched to the device connector, and is decreed by the manufacturer of the device. If you use the wrong impedance - you will get a mismatch and power will be reflected back into the transmitting device, which causes standing waves in the transmission line - things get hot and you can blow the final amplifier stage of the transmitter. Basically, you will get much less signal if you use the wrong impedance - its all about maximum power transfer.

Look at the device, it will state on the label what impedance it is, get the appropriate impedance cable from your supplier, with the correct connector on it. Pay a bit more for the connector, as cheap ones affect the impedance matching, and again adversely affect the transfer of signal strength.

Getting it wrong at best means you get a poor signal level, at worst it blows the transmitting side of the equation.

You can get you cables made up for you, or buy them off the shelf, which means they will be too long in all likelihood. Try avoid daisy chaining short cables as the connectors all add loss.

The one thing that you didn't say was are you talking about coax (which I assume is what you are talking about) as ethernet is usually run over CAT5e or CAT 6 cable (lower loss) Ethernet can be run over coax, but the transmission is incompatible with CAT 5/6 cable. This is where you will have the difference between the 2 impedances you mentioned, and where the manufacturers equipment will state the right one (in all likelihood 75 ohm)
 
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Try to avoid taking advice from people who are guessing, it will cost them nothing to get it wrong.

PM me if you want and we can chat on skype and I'll talk you through it.
 
See Mick's last comment, although I am pretty sure it is 75 Ohm cable. I actually replaced my Virgin media cable from wall socket to modem with Belden 3gb 75Ohm micro coax, makes it easier to cable manage when it is about a third of the thickness of normal coax..
 
mick cooper said:
The two types of cable are usually the difference between TV type applications and radio.

The impedance of the cable - the figure in Ohms is matched to the device connector, and is decreed by the manufacturer of the device. If you use the wrong impedance - you will get a mismatch and power will be reflected back into the transmitting device, which causes standing waves in the transmission line - things get hot and you can blow the final amplifier stage of the transmitter. Basically, you will get much less signal if you use the wrong impedance - its all about maximum power transfer.

Look at the device, it will state on the label what impedance it is, get the appropriate impedance cable from your supplier, with the correct connector on it. Pay a bit more for the connector, as cheap ones affect the impedance matching, and again adversely affect the transfer of signal strength.

Getting it wrong at best means you get a poor signal level, at worst it blows the transmitting side of the equation.

You can get you cables made up for you, or buy them off the shelf, which means they will be too long in all likelihood. Try avoid daisy chaining short cables as the connectors all add loss.

The one thing that you didn't say was are you talking about coax (which I assume is what you are talking about) as ethernet is usually run over CAT5e or CAT 6 cable (lower loss) Ethernet can be run over coax, but the transmission is incompatible with CAT 5/6 cable. This is where you will have the difference between the 2 impedances you mentioned, and where the manufacturers equipment will state the right one (in all likelihood 75 ohm)
Click to expand...

Great advice there Mick, many thanks. Will check the Superhub to see if any mention, will also check the current cable (supplied by VM) as I understand they state such things on the cable.

Might bother you later :D
 
Boonie said:
See Mick's last comment, although I am pretty sure it is 75 Ohm cable. I actually replaced my Virgin media cable from wall socket to modem with Belden 3gb 75Ohm micro coax, makes it easier to cable manage when it is about a third of the thickness of normal coax..
Click to expand...

What's the '3gb' part about Boonie?

If it's less thick then a real bonus!! I have to feed the cable through the gap in the window (it's a slide sash window) as I cannot drill in it (listed building!) so anything thin is great.

Cheers
 
Papercut said:
What's the '3gb' part about Boonie?

If it's less thick then a real bonus!! I have to feed the cable through the gap in the window (it's a slide sash window) as I cannot drill in it (listed building!) so anything thin is great.

Cheers
Click to expand...

micro coax has far greater losses on it than the thicker stuff, its down to the transverse wave flow down the cable. In addition the thicker the core (centre conductor) and the better the shield, the better the propagation. Micro coax is used for very short distances, mostly between sub units of a device working at super high frequencies. 3Gb on his coax is probably a bit of BS telling you that it will work up to 3Gb, without ever telling you that its good for those freq, up to 5cm in length.

If you have to re route 20' then you need a minimum of standard thickness coax. Having said that I would need to know what frequency the carrier on the coax is working at, as the actual data will probably be less than 30 Mhz.
 
I'm 4 hours behind you, assuming you are in UK, so if you want to get home and contact me you are welcome to, skype me if you like, mickcooper in Bermuda should find me.
 
Boonie said:
Have to say I have quite a long run (5m) and have not had any problems with data speed.
Click to expand...

as I said (or tried to!) at the higher freqencies, it will perform much worse than lower ones. 3Gb down a coax is right at the top end of coaxial performance using low loss hardline coax 1.5" thick. Your system might work ok because you are throwing a big signal down the coax and the losses whilst severe, might still leave more than enough signal at the end to work without loss of data.

I am at a bit of a disadvantage, as I have no idea what is coming out of the virgin box, what presentation it is - both physical and electrical. I can guess, but thats going to be no consolation if papercut spends money and I've got it wrong

hopefully that makes more sense now
 
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