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Sky+ cable issues

gj9358

Standard Member
Hi all,

I have sky+ in my front room, the twin coax cable which was installed by sky has been run under the skirting to the furthest alcove in the room. We have now had a re-structure so I needed the sky+ box in the other alcove. I didnt want to tear up the skirting to release the long cable, so instead I cut the small piece of cable still visible (which comes in by the alcove I want the TV in) in order to use F-connectors and a new piece of cable to add on to make a new length leaving the old behind the skirting.

I bought a length of cable from maplins (Twin Satellite Coax Cable : TV, Satellite Coax Cable : Maplin)

which i added f-connectors (4) to each end and also to the newly cut end of the existing cable and connected them with two joiners. However, the new piece of twin coax from maplins is a lot thicker than the original cable and so I have had to use tape on the original cable in order to attach the two screw fit f-connectors.

I managed to get all this done and all seemed to be ok, until we started to drop channels. Channels would not work then they would come back and a different one would go. I have re-done all the connectors making sure the right amount of copper is exposed but cant figure it out.

Has anyone got/had a similar issue? Remember I have not extended the cable in length so dropping signal due to extension cant be it.

I have now bought a new lenght of cable which has the connectors pre-fit so I can not worry about my handy work.

please help a frustrated man out.

Cheers all

Gareth

PS - sorry it's War & Peace
 

AV COM

Prominent Member
AVForums Sponsor
There should be no need to use tape on the existing smaller cable for the F connectors to screw on. The screen should make contact with the F connector. Smaller F connectors are used on the mini cable, you should be able to simply un-screw the ones from the end where your box used to be and use these.
This video shows how to do it if you've only got a knife, no fancy stripping tools like the professionals use.

YouTube - Intalling an F connector
 

gj9358

Standard Member
Thanks for that. I cant get hold of the original f connectors as they are now behind furniture. I have taken off the f connectors about 5 times to check that there is no braiding touching and that the copper center is exposed correctly and still no signal.

The only thing i can think of is that i cut the braiding and the sheath off instead of twisting and folding it over. Is this a problem with regards to earthing the cable? I cant see how this would mean no signal though.

I have even taken off the f connectors off the original cable and put the raw cable into the back of the box and still no signal. cant figure this one out.

:suicide:
 

Alan Mac

Prominent Member
The outer metal braid and copper screen must make good electrical contact with the metal body of the F connector.

The low noise block (LNB) mounted at the antenna “dish” end of the cable is powered via the centre conductor with the outer screen providing the return path at DC (and at 22 kHz for signalling). Hence the need for good (low resistance) electrical connections for both the centre and the outer conductors.

Also, the F connectors used must be of the correct dimensions to fit the cable to ensure a connection without severe reflections of the TV signals. The twin (“shot-gun”) cable uses different (smaller cable entry) sized F connectors.


Alan
 

gj9358

Standard Member
Ah that might be the problem then. I literally cut off all the excess copper braiding and cover thinking it was just structural. Would this mean the signal wouldn't work?

Therefore my f connectors have no contact with the copper braiding or cover
 

Alan Mac

Prominent Member
Ah that might be the problem then. I literally cut off all the excess copper braiding and cover thinking it was just structural. Would this mean the signal wouldn't work?

Therefore my f connectors have no contact with the copper braiding or cover

The satellite television signals as received by the antenna at the focal point of the “dish” reflector are extremely weak. They are also at a very high frequency (roughly 12 GHz). It would be completely impractical to provide the extremely expensive wave-guide required to carry this very weak microwave signal to the television receiver inside the house.

Instead, the microwave signals are frequency down-converted as a block to the 1 GHz to 2 GHz region and their power amplified by a factor of about one million times. It is this amplified lower frequency block of signals that is sent down the coaxial cable to the (in your case Sky+) receiver.

This electronic frequency changer and amplifier is referred to as a “low noise block” (LNB). The electrical energy to drive this LNB electronics comes from the satellite receiver and uses the coaxial cable centre conductor and outer metal screen to conduct the current.

It is therefore essential that the F connector body is electrically connected to the cable screen. Otherwise there will be no power to the LNB and thus no signal will be fed down the coaxial cable to your receiver.


Alan
 

gj9358

Standard Member
:facepalm: that must be it then. bloody annoyed now cos i've booked a sky engineer for Friday now. Although still had issues with the sky box (taking a hour to come out of standby) so maybe i should keep the booking so he can sort that out along with the cable whilst he's there.
 

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