Jump to content

Satellite co-axial cable connectivity


Stilllearning

Featured Posts

Hopefully this is just me being slow/stupid. Having just had a new kitchen we decided to have the satellite tv cabling hidden behind the studding, with a nice neat socket on the wall, to make a nice change from cabling along the floor. Today, having got hold of the appropriate male to female co-ax link cable to go from wall socket to satellite box, we cannot get any signal. Upon reverting to the old system of a length of co-ax direct from dish to satellite box, it works fine.

So, how can one verify the continuity of circuit in co-ax? We have a multimeter, so is it as simple as checking there is a circuit through the inner and outer of the co-ax?

Link to comment
Share on other sites

9 minutes ago, john6767 said:

Checking the continuity has to be the first step.  Also are you certain the the coax used was for satellite, it has a different impedance to the coax used for TV aerials.

No idea about which cable, and tbh, had no idea there was more than one version of co- ax.

Gulp, there’s 20 metres of it behind the wall....

Link to comment
Share on other sites

43 minutes ago, Stilllearning said:

No idea about which cable, and tbh, had no idea there was more than one version of co- ax.

Gulp, there’s 20 metres of it behind the wall....

The spec of the cable is often printed on the outside of it.

 

not sure of it is the wrong impedance it would stop it working totally, so check the continuity, and as has been suggested for a short between the inner and the shield, a nail or screw could have need put through it perhaps.

Edited by john6767
Link to comment
Share on other sites

Impedance is very likely to be 75 ohms as most are for TV, satellite or terrestrial.  If it were 50 ohms, over 20M it will likely make a little difference, although using the intended impedance cable would certainly be best.  Assuming it has not had a nail driven through it, it is almost certainly a stray strand of the braid at one end or the other, touching the centre core of one of the connectors..

Edited by Nickhlx
Link to comment
Share on other sites

The signal you're dealing with is absolutely tiny and easily diminished to a level where you'll not get sufficient at the receiver.  Use WF100 coaxial cable, keep the joints to a minimum, make sure they're all F-type connections and not standard TV ones.  Apply a bit of silicone grease or vaseline when you make up any connections to keep the damp out as this will drag the signal down quite quickly and you'll be back to square one.  Anything not complying with that list could be why you can get a picture by wiring direct, but lose it once you introduce other elements.  

Link to comment
Share on other sites

3 hours ago, john6767 said:

Checking the continuity has to be the first step.  Also are you certain the the coax used was for satellite, it has a different impedance to the coax used for TV aerials.

I thought they were both 75 ohm? 50 ohm is unusual for tv etc. Used it a lot for amateur radio stuff. 

Agree with previous poster. Reduce number of connectors, check for stray wires at each end and don't put nails through the coax.

Link to comment
Share on other sites

3 minutes ago, Dr Bob said:

I thought they were both 75 ohm? 50 ohm is unusual for tv etc. Used it a lot for amateur radio stuff. 

Agree with previous poster. Reduce number of connectors, check for stray wires at each end and don't put nails through the coax.

And make sure it is satellite spec and not tv spec as tv cable has big losses at satellite frequencies.

Link to comment
Share on other sites

24 minutes ago, Dr Bob said:

I thought they were both 75 ohm? 50 ohm is unusual for tv etc. Used it a lot for amateur radio stuff. 

Agree with previous poster. Reduce number of connectors, check for stray wires at each end and don't put nails through the coax.

Perhaps it is the same impedance, but I am sure it is different in some way, but what else is there other than impedance?  At home I have lengths of both, but on the boat so I can't check them.

Link to comment
Share on other sites

9 minutes ago, john6767 said:

Perhaps it is the same impedance, but I am sure it is different in some way, but what else is there other than impedance?  At home I have lengths of both, but on the boat so I can't check them.

As chewbacka says, it may be the dB loss on the cable. More likely though to be a short. First job is to check continuity of the center conductor and then the earth and then check no path from center to earth. You've not got any tv type amplifier in the line have you...... that would stop it working?

Link to comment
Share on other sites

1 minute ago, Dr Bob said:

As chewbacka says, it may be the dB loss on the cable. More likely though to be a short. First job is to check continuity of the center conductor and then the earth and then check no path from center to earth. You've not got any tv type amplifier in the line have you...... that would stop it working?

It's not an "earth" Bob, it's a screen.  The better the screen, the lower the signal loss.  The wigglies travel along the core and the screen keeps interference out and those good wigglies in.  Good coax has a copper core and both a copper mesh and a copper (or aluminium) foil. The other kept difference is in the dielectric - the white stuff between the screen and the core.  The old spec cable which worked ok with TV signals had a less effective plastic tube with spokes along which moisture could travel, whereas the better stuff has a foam dielectric which is more impervious.  The stuff we should be using is WF100 (or equivalent), although you can get away with RG6 particularly if it's kept dry, a short run and/or with a strong signal, so some will justifiably swear blind by whatever appears to work for them. Same arguement applies to the push in TV connectors versus the far better F-type.  If lesser stuff is working in an application, fine, but WF100 and F-type connectors is a better starting point.

  • Greenie 1
Link to comment
Share on other sites

2 hours ago, Stilllearning said:

First bulletin after brief foray up on roof:

The cable we have is rated 17 PATC, which is, I think, rated as losing 17 ohms per 100  metres of cable.

I dont think it is ohms. Signal loss is normally quoted as dB loss of signal. The signal loss is therefore logarithmic so not easy to estimate in your head.

Link to comment
Share on other sites

1 hour ago, Dr Bob said:

I dont think it is ohms. Signal loss is normally quoted as dB loss of signal. The signal loss is therefore logarithmic so not easy to estimate in your head.

A quick google shows it is signal loss of 17dB @ 800MHz.  From memory The signal from the dish lnb to the set top box is 1 to 2GHz.  No idea what the loss is at those frequencies but it will be much worse.   Mr Google seems to think your cable is suitable for domestic satellite systems, though probably a better cable is needed for very long runs.

Link to comment
Share on other sites

35 minutes ago, Chewbacka said:

A quick google shows it is signal loss of 17dB @ 800MHz.  From memory The signal from the dish lnb to the set top box is 1 to 2GHz.  No idea what the loss is at those frequencies but it will be much worse.   Mr Google seems to think your cable is suitable for domestic satellite systems, though probably a better cable is needed for very long runs.

Agreed. For a short run on a boat ie <10M I would think any good cable will do.

Link to comment
Share on other sites

2 hours ago, Dr Bob said:

Agreed. For a short run on a boat ie <10M I would think any good cable will do.

The biggest killer of the tiny, tiny signal we're looking at here is probably moisture.  Boats are inherently a damp environment, plus we're usually making and breaking connections pretty frequently. Any good cable might indeed do... that'll be WF100 then! (Did I mention F-type connectors and vaseline?) 

Link to comment
Share on other sites

20 hours ago, john6767 said:

Perhaps it is the same impedance, but I am sure it is different in some way, but what else is there other than impedance? 

Capacitance. 

 

Thought I’d answer seeing as nobody else did. 

Link to comment
Share on other sites

53 minutes ago, Stilllearning said:

Problem fixed   :)   (why isn’t the emoticon thingy working?)

 

the problem was was simply that the inner cable, that holds the wriggly things, thanks Sea Dog, wasn’t quite getting into the LNB socket, doh!

Anyway, back to Bake-off Extra Slice.

 

Ah, an air gap - that'd do it!  Glad to hear you're back in the tent ;)

 

Link to comment
Share on other sites

1 hour ago, Stilllearning said:

Problem fixed   :)   (why isn’t the emoticon thingy working?)

 

the problem was was simply that the inner cable, that holds the wriggly things, thanks Sea Dog, wasn’t quite getting into the LNB socket, doh!

Anyway, back to Bake-off Extra Slice.

 

There you go. Vaseline (ex Sea dog)  is good at getting wiggly things into tight sockets and protecting them.

Should I get my coat?

  • Haha 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.