satellite dish head broken?

[mzjo]

Our satellite dish has stopped working. I have tested the continuity between box and head which is fine. Which leaves the box and the head. While testing the cable we observed that the head was open circuit.  I would have expected a measurable impedance, imagining that the inside is an affair of coils and stuff. Does an open circuit mean that the head is the probable source of trouble?

[Hot Flatus]

Don't know but the LNB  (what you refer to as the head) is cheap and easy to replace

https://www.maplin.co.uk/c/audio-entertainment/aerials-satellite/satellite-dishes-lnbs

https://www.amazon.co.uk/satellite-lnbs/b?ie=UTF8&node=528560031

[Brucey]

the impedance is with respect to RF signals. There is a DC bias (supplied by the box) to power the LNB.

 I'm not sure you will get a sensible resistance reading using a multimeter on the LNB.

cheers

[Kim]

LNB isn't covered in snow, is it?

[mzjo]

LNB isn't covered in snow, is it?

No, Our part of France has been spared the sibérien blizzard, just a bit cold (not the arctic climate of Brum). It always used to need wiping off in heavy rain. Fortunately it's at ground level (the dish,.not the climate). The installation is about 15 years old. The replacement LNB will undoubtedly come from the local shop who sold me the original bits, it's just a help to know if I need to take him Canalsat's box as well (he is an agent for them).

[Feanor]

<ETA> I didn't know you were not in the UK.
Everything I've posted below relates to UK Sky/Freesat from the Astra cluster.
It may not apply to your setup.</ETA>

The innards of an LNB are not just coils and stuff, it's a fairly complex bit of magic RF electronics.
There's no test you can do with a simple meter on it.

The tuner(s) in the sat box provide power and switching signals to the LNB to tell it what channels to send down the cable.
For various reasons, all the channels can't go down one cable at the same time, unlike a normal TV aerial.

I'd go into the setup menu on the box and look at signal strength and quality.

Then, I'd probably do part swapping starting with easiest first.
So a different sat box first.
Then I'd probably bring the box up close to the dish, and run a length of known-good cable.
Then I'd put my signal strength meter in-line between the LNB and box. ( Could the dish have moved? )
Then I'd be looking at swapping the LNB.

[Kim]

After 15 years, it might also be that the coax has gone a bit soggy...

[orienteer]

Our dish cable was once chewed by squirrels!

[Feanor]

After 15 years, it might also be that the coax has gone a bit soggy...

Absolutely.

Which is why I'd want to bring the box up near the dish, where I could use a known-good short-ish length of cable with a couple of screw-on F-connectors to eliminate the existing cabling from the equation.

Also, the OP didn't mention any fancy distribution systems with multi-switches or multi-LNB DiSEqC switching, so I remained silent on that...

[mzjo]

Ok a bit of further information.

The dish is still properly aligned
The "pointage" in the menu indicates no signal at all from the dish.
The breakdown was a sudden one rather than a deterioration over time. I was in hospital being chopped up when it happened. My daughter managed to play with the box menus to get a signal but it didn't last.
The installation has a single, unbroken cable from the dish to the box. No junctions, amplifiers or whatever. No fancy bits of flat cable for passing doors or windows. The only weakness is that the run has 16m outside and 1m in the house. Outside cable is protected as far as possible in a rigid conduit.
The only test has been à continuity test which gave infinite resistance with the cable connected to the LNB (box disconnected to measure at the box connector) and zéro resistance with the cable disconnected from the LNB and the two lines coupled. The LNB returns infinite resistance but as has been pointed out that may be of no relevance.
Yes I am in France and we have had some pretty cold weather while I was in hospital.
I hope that makes it a bit clearer.

[Asterix, the former Gaul.]

After 15 years, it might also be that the coax has gone a bit soggy...

When I put my dish up in France I carefully led the co-ax through the black metal arm.  A few years later when I replaced the lot I found the heat inside the arm had baked the co-ax so that it was extremely brittle and just fell apart.  I didn't put the new cable inside the arm!

The satellite signal in mid-France arrives very low on the horizon and it doesn't take much movement of the dish to lose the signal.  It is usually simple to fit a new LNB and it's quite likely to be an improvement on the old one even if it wasn't bust.

[Diver300]

I would change the LNB on the principal that they are cheap and easy to change, and could well have suffered from being left outside for 15 years.

[mzjo]

After 15 years, it might also be that the coax has gone a bit soggy...

When I put my dish up in France I carefully led the co-ax through the black metal arm.  A few years later when I replaced the lot I found the heat inside the arm had baked the co-ax so that it was extremely brittle and just fell apart.  I didn't put the new cable inside the arm!

The satellite signal in mid-France arrives very low on the horizon and it doesn't take much movement of the dish to lose the signal.  It is usually simple to fit a new LNB and it's quite likely to be an improvement on the old one even if it wasn't bust.

I don't have any metallic conduit, the cable runs under thé LNB arm, down the outside of the mast (about 1m above ground) and into a plastic conduit, partly buried and on the north side of the house. The only place where the cable can heat up is at the front of the house where it climbs 2m and I can inspect it very easily. It looks ok externally.
Fitting a new LNB is indeed very easy with the dish at ground level. Amazing but thé dish bas never gone out of alignment, even when I bump it with the lawnmower!