Coax cable problem

[rick19011]

I lost the connector to the coax cable long ago so only the copper wire in the cable was pushed into the input of the satellite receiver, this has made the cable lose and it sometimes displays no/bad signal because of this, so i used a pair of scissors to cut the cable so a fresh part of the copper wire was visible, but now I am getting no signal at all, am I right in saying all I will need is a wire stripper and a f connector? I don't want to call somebody out on something so small, thanks.

[termiantor]

I lost the connector to the coax cable long ago so only the copper wire in the cable was pushed into the input of the satellite receiver, this has made the cable lose and it sometimes displays no/bad signal because of this, so i used a pair of scissors to cut the cable so a fresh part of the copper wire was visible, but now I am getting no signal at all, am I right in saying all I will need is a wire stripper and a f connector? I don't want to call somebody out on something so small, thanks.

correct mate f connector all u need

[Manic01]

You may well have shorted the lnb now.
yes a f connector is all you need.
[ame=http://www.youtube.com/watch?v=v2v7fLHZzzM&feature=related]How to wire an F connector - YouTube[/ame]

[cactikid]

yep thats why they use a threaded joint cant be loose,buy a few spares also.

[ramjet]

bear in mind the outer sheath is the earth, so you need to bend that back over the insulation, ensuring none of the strands is touching the centre conductor, and have the centre conductor protrude a couple of mm past the screw on end of the f connector

its a 5 minute job for maybe twenty pence for an f connector

[digicon]

bear in mind the outer sheath is the earth, so you need to bend that back over the insulation, ensuring none of the strands is touching the centre conductor, and have the centre conductor protruse a couple of mm past the screw on end of the f connector

its a 5 minute job for maybe twenty pence for an f connector

The outer Braid is in fact not an earth its just a woven copper shield, Sat Coax is made up of the following.

1. outer plastic sheath
2. woven copper shield
3. foil copper shield ( not on all cables )
4. inner dielectric insulator
5. copper core

The main reason the woven copper shield is bent back is to allow for a better grip for the external connector whether it be an 'F' or a standard Aerial Plug.

[ramjet]

The outer Braid is in fact not an earth its just a woven copper shield, Sat Coax is made up of the following.

1. outer plastic sheath
2. woven copper shield
3. foil copper shield ( not on all cables )
4. inner dielectric insulator
5. copper core

The main reason the woven copper shield is bent back is to allow for a better grip for the external connector whether it be an 'F' or a standard Aerial Plug.

whilst I appreciate that info I cannot agree with you

no its not an "earth" in the sense of being tied to an actual earth itself

but when used on satellite to get 13 volts or 18 volts to the lnb you need 2 wires, as you do with any voltage, and the "earth" I was referring to is "earth" compared to a positive potential difference of either 13 volts potential difference (measured to "earth" with an AVO meter), or 18 volts potential difference (measured to "earth" with an AVO METER), or measured to "neutral"

so let me say its NEGATIVE , but considered at earth potential, compared to the inner conductor which would be a positive potential when compared to it of either zero ( receiver off, or 13v or 18v if the receiver is on depending on H or V)

so to say it has no use is certainly not in my book, as electrically speaking it is what electronics engineers call "earth" when compared to positive voltages

its called an "earth" on a car but isnt actually connected to earth, but the name is used all the time as 12 volts and earth (or neutral)

in other words it carries electricity to complete a circuit and without it I believe the lnb and motor would not be powered and therefore not work

but as boxes are no longer "earthed" in the sense that they only have 2 wire mains leads and no "earth" , so I will rephrase it as being "neutral"

its also required to help to shield the centre conductor from stray signals too, so from a psu point of view it is neutral when compared to the positive voltages most psu`s put out

so my point was it is part of the 2 wires required to make the system work, by powering the motor if fitted, and lnb in any case

so the main reason for it being required and bent back is actually to provide one "leg" of the 2 "leg" voltages used to power the lnb , or the motor and lnb and was the point of my reply and totally omitted from your detailed reply which is correct in its manufacture and some of its properties, but not the electrical conductance that it is used for

try removing it by cutting it off , then see how far you get on one inner conductor

even on the rf output its tied to the "earth" or "neutral" of the cage the box resides in (as in faraday cage technology), and is used to help conduct away any stray interference, otherwise we could use a single wire or a coat hanger (which would work) but its always been this method even when tv sets were earthed and was there to stop interference to the inner conductor, hence why its coaxial 2 wire cable, and one reason its copper or aluminium too

[digicon]

Sorry Ramjet i cannot agree with the statement

in other words it carries electricity to complete a circuit and without it I believe the lnb and motor would not be powered and therefore not work

You can literally leave all the shielding off and just stick an 'F' connector on and the Motor and LNB voltage will still work no matter what, I did not say it has no use if you look it up officially its just another shield, I have actually seen Jobs and not just motorised or standard dish installls where no braid has been left or bent back and the install still works.

[ramjet]

well we will just have to disagree on that score because in all my electrical training you need a positive and a negative to achieve a potential difference and all sat boxes use 13 volts and 18 volts, with the centre conductor as the positive and the outer conductor as the "earth"

so I stand by what I wrote seeing as I went through years of training on these matters and a positive voltage needs a reference point of neutral or earth or "ground" to make it work

on an avo meter you wont see 13v or 18v if you only stick the red positive lead on the centre conductor, that is for certain as I just tested it !

but place the black negative lead on the outer case of an f connector and you do see the potential difference (the voltage)

[Manic01]

Not getting involved here

[cactikid]

so can under powering something at a latter stage have a knock on effect?
what about the other cables on the lnbs if one of them was earthed would the whole lot be earthed then?

[digicon]

Ramjet i am in no way having a go or anything i am just stating what i had to re-learn for my RDI with birmingham college over 2 years, if your background is in electrics then fair enough but i know for a fact the outer braid is a shield and nothing else it does not carry any voltage, all shielding is bent back so as not to interfere with the main copper (signal) core

[ramjet]

seems to me that isnt the case, its not just a shield on a diseqc or lnb connected sat cable as I already pointed out

sat boxes give out 13 volts and 18 volts as you are well aware, and to test for a potential difference of 13v and 18v you need a reference point tied to "ground", common slang term is earth

same applies on a car battery , 12 volts positive potential compared to "earth"

I thought I made this clear in my posts ? and that was the reason I replied to the OP

try measuring it with an avo meter and see what happens. no voltage until you "ground" the earth flying lead

you say it carries no voltage, well it wont seeing as its at "earth" potential ! that is the point of grounding electrical circuits, to have no voltage

but it carries current which is how an lnb or motor operate

the centre conductor has the voltage (the potential difference), and the outer sheath is used to complete the electrical circuit in order to carry the current

for radio interference shielding its normally "grounded" at one end only, and no it wont have any voltage, like a tv aerial lead, but for satellite motors and lnb`s there is the voltage to consider as well as the rf signals

so my original answer reflected the problem of bad signal due to having no electrical return path for the lnb current IF the outer sheath was cutoff or if there was no dc path

I am not saying members have not found a motor or lnb working without the return path as a potential difference (a voltage) will always be positive with respect to anything else, which is why lightning grounds itself or is why pylons carry massive voltages but birds are not killed when they sit on them, but if you grounded the bird !!! the current would be lethal

as I said earlier, I tested a tm1500 here with a multimeter and no voltage exists until you use both leads, sticking the positive lead to a centre conductor does not show 13v or 18v, as you need the negative black lead to provide a reference point to show the potential difference, this can be either the outer part of the F connector, or an actual earth itself like on mains supplies or a copper earth spike buried in the ground

try testing what I said, instead of relying on what college may have taught you in RDI and failed to mention the use of 2 conductors to provide a potential difference (a voltage)

obviously the outer core carries no voltage, as its not supposed to , as its at "earth" potential, or would be if we still earthed psu`s

also try the multimeter as a current monitor in series with the outer cable, and then see if current flows when the lnb is connected (it will so its an electrical conductor too)

[Manic01]

Best let this go before it turns into some kind of serialisation

[dick b]

sorry cant let this one go. ramjet is 100% correct you must have a return path for the current and no way will a motor or stb work with just the central electrode connected if you cut the shielding off and screw an f-plug it must make some contact with the shielding to work.