RG6 versus RG58 1

[Finnick]

Hello to all;
I'm looking for some info on the coaxial cable standards for RG6 and RG58. I have been able to see that the RG58 is a 50 Ohm cable and the RG6 is a 75 Ohm cable. What I was really after, and I was unable to find was an accurate comparison of the distance propogation capabilities of each for composite video signals. I have done numerous searches on the net and found only sales sites, one of which did say that the RG6 cable can be used up to 1000 feet. Can anyone tell me where would be a good site for the info on these cables? Or if anyone knows their ratings right offhand, that would be great, too.

Thanks in advance

 

[BrianR]

Finnick,
A comparison of losses shows
RG6 ~= 0.7dB/100ft @ 10MHz, 3dB/100ft @ 100MHz and 7.4dB/100ft @ 400MHz.
RG58 ~= 1.5dB/100ft @ 10MHz, 5.6dB/100ft @ 100MHz and 14dB/100ft @ 400MHz. This shows that RG6 is good for 2x the distance of RG58.

As for the maximum distance that any coax is good for, it depends upon how much loss you can tolerate and how much noise pickup will happen.

I'd say 1000 ft offers an excellent opportunity to collect a lot of noise and a triax cable sounds more appropriate unless your video bandwidth is fairly low or there is natural shielding in the installation. RG6 is a much better cable for this application as it generally has better quality shielding.

Consider composite video for computer monitor quality signals to have 100MHz bandwidth. As an example calculation, assume 1000ft of RG6, loss = 10x3=30dB, input signal of +10dBm and induced noise of -30dBm at cable output. Losses for the signal in the coax will give a signal output of -20dBm and noise is still -30dBm, so the s/n ratio is only 10dB which is very poor.

 

[Finnick]

Thanks, BrianR - that gives me a good amount to work with - I suppose if I wanted to get really detailed in my anlysis of this, I should dust off my transmission cable textbooks and find the formulas I need - I just wasn't sure of all the ratings for these types of cables. BTW the actual lengths we are using will be nowhere near 1000 feet, maybe 200 or 300 max, and we do have a DA to boost the signal levels, so things shouldn't get too bad.

Thanks again for the help

 

[jbartos]

Suggestion: To do any meaningful analyses of the above coax cables, their data sheets will be needed. Visit

http://www.swissatv.ch/documents/CoaxTable.pdf

for useful data.

 

[Finnick]

Thanks - that is a great reference!

 

[Iden]

Concider for comparison the RG-59 cable. It is 75 Ohms. With RG 58 you are not comparing apples to aples.
RG-6 has inherit lower loss merely by the size of the conductive element.

Iden