Weird one, problem on multi switch

[Scubadan77]

a friend ask me to have a look at a problem they are having.

It is a communal 1.9m dish with quartro lnb going to a 16 feed switch. the prblem they are having is they are getting brake up at night. the cable run is no longer than 30meters to the house and no one else is complaining.
I tried changing the port on the switch first awhile ago but still happening. tonight i looked a bit more, his box only had vertical transponder scan in , Horizontals there was no signal. put my meter on and signal was strong for both V and H so I thought i would try with another box. on this box there was no problem with Horizontals but when i went to the vertical transponders there was no signal !!!!

scratching my head, gratfully for any advice..thanks

 

[Terryl]

How low to the horizon is the dish pointing?

If around 20 degrees or less, then it could be a signal skip, sometimes when the ground temperature is just right the signals from a source low to the horizon can skip (like a rock in a lake) this skipping causes the signal to be out of phase from the main one, if the skipped signal id strong enough it will cause a phase cancellation, this can happen on horizontal and vertical signals.

This is a best guess.

One other possible problem is a bad coax to that box, can you move that box to another location and try it out?

Or move the box up to the switch and try it there?

 

[Archive4]

I was working yesterday on a house with a quad lnb ( no multiswitch ) but with a very interesting and possibly related problem.
The living room box would only receive Vertical txps with no other boxes connected, bedroom 1 was working ok most of the time, bedroom 2 worked as and when it felt like it!
Living room box worked ok when bedroom box was powered up and on a Horizontal txp.
Three problems were causing the problems.
Bedroom 1, faulty f-type connector occasionally not passing signal between cable and screw nut due to intermittent connection on collar.
Living room, when checked with meter, signal level was -63 dB due to degrading joint on the roof which was causing excessing loss on the signal on both H & V, but was effecting H more. Remaking joint brought signal level up to -50 dB which is well within the box limit.
Bedroom 2, again receiving signal at box end of cable at -55 dB. Remaking joint on roof brought signal up to -50 dB and box was happy. Should have been ok at -55 dB but it was an older Sky box and needed more signal to be happy.
I must point out the snr on the meter was showing ok ( 10ish dB ) even at - 63 dB.
( As a precaution I disconnected the fourth feed from the LNB as it had about a 35 M cable run and never has anything connected )

Things to check, signal level and snr on multiswitch output and the same at the box end of the cable. Check, and if possible remake any joints, even if they do not look too bad as sometimes it can effect the signal even when it looks ok ( had that before with iffy straight connector )
Also, bear in mind most multiswitches have variable gain for each output, and some also need to be balanced or will cause problems.
Could be the gain is wound down on the both the original and second output you tried.

Let us know how you get on!

 

[A nonymous]

Is it just channels on the UK spot beam you are losing or is it the signals on all the European beams

The only dish i've worked on with in that part of the world was a 2.4m dish in Cala'n forcat in Menorca about 10 years ago. The signal for BBC 1, 2 and 3 used to disappear at about 7pm and come back about 4am, Outside of these times the signal quality was usually ok. As far as i was aware this was caused by the satellite moving around inside its orbital location, When it moved to the far side of its orbital position signal was lost as the footprint moved out of sight of the dish.

This only usually affected stuff on the UK spot beam and European North beam.

 

[Scubadan77]

sorry been away for easter...

Terryl , if the signal was skipping would this not effect every one off the dish???

but I think trying the box else were and try at the switch first is a good starting point.

Things to check, signal level and snr on multiswitch output and the same at the box end of the cable. Check, and if possible remake any joints, even if they do not look too bad as sometimes it can effect the signal even when it looks ok ( had that before with iffy straight connector )
Also, bear in mind most multiswitches have variable gain for each output, and some also need to be balanced or will cause problems.
Could be the gain is wound down on the both the original and second output you tried.

Milamber,this also what I need to look at, there is a couple of joints along the way so I will remark them all.

I will be going back this week so will let you know what I find and if I fix it...

thank you all for your advice!!!!

 

[Terryl]

Sorry, I didn't see the part about others on the system, old eye balls getting to me.

Best bet is a bad connection somewhere, or someone put a coax staple through the coax jacket a long time ago and the problems are just showing up now. (water got into the coax)

Or a bend in the coax that is too sharp of one, RG-6 (or it's equivalent) should not be bent at a sharp right angle, but at a radius no smaller then lest say your wrist, a very sharp bend (or a kinked coax during pulling it) can over time cause the center conductor to move too close to the shielding, this causes the 75 ohm inductance to change due to the coax capacitance changing, or if too sharp the coax resistance (not the 75 ohm but it's DC resistance) could even change over time, water can also cause a big problem if it got inside the coax somewhere and has rusted out the center conductor if it's copper clad steel.