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Coaxial cable

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Misterbenn

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Hello all,

I'm pondering terrestrial television coaxial cable. Everything that my local hardware shop sells is quite large diameter and not very flexible. So I would like to know can I / why shouldn't I use oscilloscope coaxial cable which is smaller diameter, more flexible and I suspect higher quality.

From the following URL I found out my transmitter frequency, 550MHz>f<750MHz
**broken link removed**
 
Everything that my local hardware shop sells is quite large diameter and not very flexible.
Generally speaking, the greater the diameter of the coax cable, the lower the signal loss.
The higher the frequency of the signal, the higher the loss in the cable. From memory, the loss is proportional to the square root of the frequency, eg 4x the frequency gives 2x the loss.

why shouldn't I use oscilloscope coaxial cable which is smaller diameter
What is "oscilloscope coaxial cable" ?
If you mean the cable used for oscilloscope probes, that is not a good cable to use as a transmission line. The centre conductor is a VERY thin wire in order to give a very low capacitance cable.

It may be possible to use a smaller diameter coax cable for your TV.
The things you need to consider are:
The received signal strength
The loss per metre of the cable
The length of the cable
The signal level required at the receiver.
Whether this will work in your case is impossible to say with the imformation available.

One thing which has not been considered so far is the characteristic impadance of the cable.
Television antenna systems are designed around an impedance of 75 Ohm, so you should use 75 Ohm cable.
Another common impedance is 50 Ohm. Using a 50 Ohm cable in your application may be OK, but there is a chance of some rather odd effects happening to reduce the received signal strength.

JimB
 
Thanks for the quick responses.

John, the link was helpful. The wire I have available in the lab is RG-58 which from the table does give higher losses than the recommended RG-6. However I don't believe the stuff in my local hardware shop is RG-6. Its just called 75Ohm Coaxial cable and I suspect its a copper coated steal core with the bare minimum required for a braid.

I should explain why I'm considering this. Currently I have the receiver in the attic with the TV downstairs and a standard consumer coaxial cable running down the outside of the house. To me this looks ugly and as I'm planning to update the house wiring anyway I'm looking at moving the coax internal and running it with the Cat6. So to reduce the space required in the wall I got thinking about the, as I now know its called, RG-56. The run is <10m and I've not had any issues with poor signal so far.

I suspect for such a short run my RG-56 will be ok, perhaps better than what is currently installed and perhaps not. I don't think I ever know how good the 'TV coax' in the shops is.

I guess I'll run the cable and then test it prior to filling in the cable run. If I have any problems I'll go buy some proper RG-6 but I'm probably overthinking this for a simple TV installation.
 
This http://www.abccables.com/info-rg59-vs-rg6.html does a really good job of explaining thing, but I'll add a few.

In homes RG6 Quad Shield is generally used for drops or anything behind the wall. In some commercial installations RG11 is used. It's really nasty to work with. Here is a blurb on RG11 - http://www.highdefforum.com/local-h...78-questions-about-rg-11-long-cable-runs.html

Now, the cables come in copper clad and copper. For signals, it doesn't matter, because the signals travel on the skin of the conductor. For transmitter operation or rotor operation thru the coax, it might matter.

RG6 is available in quad shield which basically gives 100% shield coverage. The connectors for RG6 and RG6 QS are different. I cut the center conductor at an angle.

If you want, you can use a bit of RG59 from the wall jack to the device.

What is cable impedance? It's an impedance (Z) determined by geometry. The connector should have the same characteristic Z too. BNC connectors, used on scopes have a 50 ohm Z, but you CAN get them in 75 ohm Z. When there is an impedance mismatch, there are what's called reflections in the cable. Some of the signal gets reflected back to the sending side which you don't want.

So, if you need flexibility use a length of RG59. In walls, its actually easier to use RG6.

I typically use F right angle adapters in the wall and out of the wall.

Remember that the length of the cable attenuates the signal. 3 db of loss is a factor of 2. http://www.satsig.net/lnb/db-calculator.htm

Attenuation is frequency dependent.
 
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Really useful links thanks! Looks like I should get myself some RG-6. Took a quick look on RS and boy is that stuff expensive, when compared with the RG59 stuff
 
Really useful links thanks! Looks like I should get myself some RG-6. Took a quick look on RS and boy is that stuff expensive, when compared with the RG59 stuff

No - why would you want to use RG6?, and why on earth would you buy coaxial cable from RS Components.

Assuming you want to do a decent job (but NOT thin) you want WF100 satellite cable, double screened and with a solid copper screen - you can buy this from any TV/Aerial supplier.

You 'can' buy cheaper cable aimed at TV rather than satellite - but it's cheaper because it's greatly inferior, WF100 is a FAR better option, for little extra cost.
 
One of the sources that I referenced said that WF has a different jacket that prevents water from intruding along the inner conductor. Belden doesn't even make the cable. Strange.

If you use RG-6, use RG-6 Quad Shield
 
Here where that info came from.

http://www.megalithia.com/elect/cable/ said:
CT100 is also good and looks pretty much the same at this point. For DTT runs to external aerials, prefer WF100 to CT100 if you have the choice. WF100 has a foam inner insulation whereas CT100 has airspaced inner insulation. If water gets into CT100 it runs into the insulation and the cable can fill with water. WF100 won't do that, and is also slightly more resistant to kinking. Both are good with good workmanship.

When I search for WF100 all I see is uk sources.

CT100 also cites uk sources.

In the US, I see RG6 from a satellite supplier: http://www.rickssatelliteusa.com/rickssatellitecoaxcableandribbon.htm

See RG6: http://www.prosatellitesupply.com/

So is it a uk thing?
 
WF100 replaced CT100 a few years ago, it might well be a European 'thing', but as you've not got your location filled in we don't have a clue where you might be.
 
In the USA, cable companies are still using RG6 quad. Some aftermarket wireless suppliers advise using LMR-400 for antenna connections.

John
 
The correct cable to use for terrestrial TV is RG59.
However in recent times, a lot of people have been using RG6. (I don't use it)
There are two reasons for this. The first is that RG6 is cheaper. The second is that the cable being sold by a lot of my local retailers as RG59 was not RG59, it was a very poor quality copy.
On top of this, people using RG6 self validated their cheaper installations by quoting the lower insertion loss on RG6 cable.
Or that RG6Q (quad shield offered better protection from interference).
I've always said with regards to Quad shield on any cable. If it's not worth doing once correctly, it's worth doing four times poorly.

RG6 is much better suited to short runs on satellite TV installations from the LNC to the receiver. This is what it was designed for.
While the problems are much less noticeable with digital TV, the return loss on RG6 is all over the place causing equalisation problems.
It was not uncommon to see analog TV pictures with poor sound, colour problems or tearing pictures.

I did a big job where the customer insisted that the cable to be used will be RG6Q. They were told that this was an inferior cable and there would be problems.
They insisted. The contract was signed but a clause put in that if the system didn't work, the expense to fix it was theirs.
It didn't work and they brought in another tech to fix it. He couldn't find a fault and ended up walking away.
I convinced them to replace the entire system with RG59. If it didn't work, my company would bear the cost.
They agreed and it worked perfectly.
I later found out that one manager was responsible for the RG6Q specification and because he'd obviously read on an internet forum somewhere that it was "better" than RG59.
(I'm living the Dilbert comic episodes)

Proper RG59 cable is more expensive than the cheap rubbish sold retail. Companies like RS, Element 14 and Huber & Suhner sell good quality spec RG59.
I won't comment on their prices other than I've seen audiophiles spend hundreds of dollars on speaker cables and connectors and then skimp on the television RF cable.
You'd think these people would be running LDF4-75 into their living rooms for the money they spend on sound systems.

There is not much reason to bother with such low loss cables unless you have a long coaxial run or live in a weak signal area.
In such a case using proper RG11 is the next step up. And if for some extraordinary reason I needed something better, then I'd be considering LDF1-75 or FSJ1-75.
I have put this cable in for customers at their request, but they have very little valid reason to go to such expense.

However in the future I can't help but wonder what kind of TV signals are going to be used to broadcast 4K television or even possible higher.
When this happens I can't wait to see what happens with all the RG6 installations.
 
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