Some channels proving to be an issue

[the frenchman]

It looks like you may have a prime focus dish. This is the case where all three arms are the same length and spaced equally and the lnb is held dead in line with the centre of the dish - also the dish will be totally circular rather than a slightly elongated shape. If this is so can you also confirm it is a one piece dish - i.e. it is made of a single piece of metal rather than made up of 6 segments or petals - some poorer PF dishes are contracted like that and present a whole new problem. If indeed a PF dish then checking for warp is much easier - just fasten a piece of fine string right across the dish going from the edge and across the centre and to the far edge - then fasten a similar string at 90 deg from the first again going across the centre. If the dish is OK the strings will meet at the exactly the same point without any difference in height from the dish centre. You can add further strings at say 30 deg and 60 deg to check the entire dish is OK - if nice and tight all strings must meet in the centre at the same height. If they don't you dish is warped. Now assuming the dish is not warped the next thing to check is if the lnb is actually pointing at the centre of the dish - sometimes the arms or even the bracket can get distorted and this results in the lnb pointing a bit off centre - a simple way is to replace the lnb with a tight beam torch and check that it illuminates the dish evenly and is not pointing off centre - but for this to work you need a torch wichi is round and fits snugly into the lnb holder and these are not always easy to find. Also the torch beam may not be true so try turning it around to check the illuminated part of the dish stays the same - if the beam wobbles then its not going to work.

It is indeed a PF dish ... strings...tight beam torch

 

[joddle]

One other thing you should check if you have not already done so is the condition of the cable. Just a month ago I was losing channels which had previously been strong and it turned out to be that the cable was the problem. The casing fractures in the sun and then water gets into the mesh and things go downhill from there - a good while ago I had a similar problem and the water actually got it the receiver and caused a short.

 

[Sleepingwiththefish]

One other thing you should check if you have not already done so is the condition of the cable. Just a month ago I was losing channels which had previously been strong and it turned out to be that the cable was the problem. The casing fractures in the sun and then water gets into the mesh and things go downhill from there - a good while ago I had a similar problem and the water actually got it the receiver and caused a short.

I had exactly the same thing some time ago, first it got inside the DiSEqC switch and a port was damaged (it doesn't work but others do)
Recently I noticed water dripping out of one cable behind my TV where I have a quick disconnect of all cables that go to STB, lucky the junction stopped the water from going inside the tuner.

 

[the frenchman]

One other thing you should check if you have not already done so is the condition of the cable. Just a month ago I was losing channels which had previously been strong and it turned out to be that the cable was the problem. The casing fractures in the sun and then water gets into the mesh and things go downhill from there - a good while ago I had a similar problem and the water actually got it the receiver and caused a short.

I only put the cable in a few months ago and ran it through some 20mm flexible conduit. As you say the sun here chews it up.

 

[joddle]

Looks like its down to the dish or LNB then. Any idea of the make of dish? - as said before, a photo would help here. My setup In Javea is using a 25 year old 1.2 PF dish with an Inverto Pro C120 LNB and the original dish feedhorn and gets almost everything with pretty good SS and SQ, The skew setting took great care - a smidgen of a degree making all the difference for some channels so thats why I mark out my start position with a pencil first before moving anything. One of those beeper meters may help you with the aim - I set the receiver to a difficult channel then adjust the dish for max signal then bolt down hard and then tweak the skew. Not as good as using a pro bit of kit obviously but gets a pretty good aim. Have you tested for dish warp yet? I still find it hard to understand why you are having issues with a 1.8 dish unless something is pretty off somewhere. Are any of the arms showing any signs of previous bending or distortion?

 

[the frenchman]

Looks like its down to the dish or LNB then. Any idea of the make of dish? - as said before, a photo would help here. My setup In Javea is using a 25 year old 1.2 PF dish with an Inverto Pro C120 LNB and the original dish feedhorn and gets almost everything with pretty good SS and SQ, The skew setting took great care - a smidgen of a degree making all the difference for some channels so thats why I mark out my start position with a pencil first before moving anything. One of those beeper meters may help you with the aim - I set the receiver to a difficult channel then adjust the dish for max signal then bolt down hard and then tweak the skew. Not as good as using a pro bit of kit obviously but gets a pretty good aim. Have you tested for dish warp yet? I still find it hard to understand why you are having issues with a 1.8 dish unless something is pretty off somewhere. Are any of the arms showing any signs of previous bending or distortion?

Going back to the house in a couple of weeks I'll snap a photo then and post it.Nothing glaring looks out of line,but as you say a more thorough investigation is needed.

 

[the frenchman]

Going back to the house in a couple of weeks I'll snap a photo then and post it.Nothing glaring looks out of line,but as you say a more thorough investigation is needed.

Looks ok,not warped getting channels in the evening that I can not get during the day?

 

[Channel Hopper]

Oh dear

 

[jeallen01]

Looks ok,not warped getting channels in the evening that I can not get during the day?

An aging LNB that is OK at night when it's cooler, but changes frequency / loses stability due to daytime heat?

 

[woborny]

Looks ok,not warped getting channels in the evening that I can not get during the day?

Yes, donrt think those types of dishes dont warp!
But, you have an offset LNB on a prime focus dish...so already not exactly ideal, it will work, but not ideal.
(already mentioned in a post above)
And it also looks like the lnb is not aligned correctly so it is aimed towards the middle of the dish, it looks as if it is not aimed to wards the exact centre of the dish...?
And those dishes do not perform like the other 1.8m prime focus dishes, they are, i have found, a bit lower in signal levels..

 

[superpascu2]

In my case I have problems with CH4HD, breaks up. It has been raining water with sand in the last days. Do you think this could afect? I mean the surface of the dish is covered with sand

 

[Channel Hopper]

Normally only when dry, though it is best to clear once it gets beyond a few cms deep.

 

[a33]

@the frenchman :
When this is, in fact, a normal offset Ku LNB, the LNB viewing angle of it will be about 70 degrees.

If this prime focus dish has an f/D of probably about 0.4, an LNB viewing angle of 125 degrees could be used.
So a big part of the dish surface (more than half of it) is NOT used, now.
That would account for not so good reception...

Greetz,
A33

 

[the frenchman]

An aging LNB that is OK at night when it's cooler, but changes frequency / loses stability due to daytime heat?

The LNB is new but obviously not the correct type for the dish,I'm picking up all the BBC channels which really are the only ones that I watch often so I'll stick with it for a while.Thanks for all the helpful posts gents.

 

[joddle]

Just had a bit of a scare - I recently changed the cable feed to one of my receivers (a trusty Humax Foxsat HD) as a non Spanish speaking guest was going to use our spare room that has not been used for a good while. On tuning in the receiver gasped as channel after channel reported bad signal or no signal. In other rooms working from the same dish and LNB even the not so good Manhattens were pulling in everything without fuss so immediately suspected I had done something wrong in the cable renew. Checked from end to end and no shorts and no open circuits so for a moment or two was baffled until I remembered that sometimes my dish can overwhelm the Humax sensitive receiver. A 10db in line attenuator later and tranquillity returned. The lesson for the day - a bad or breaking up picture does not always mean a bad dish - sometimes the opposite! The stupid bit is I had done something similar a few years ago and not remembered - Duh!

 

[the frenchman]

The set up in my apartment has been playing up for a while. Over the Summer months I lost quite a few channels and put it down to the heat starting to kill the lnb. Now some have come back, but then start to drift away late afternoon and by nightfall gone altogether. I'd have imagined if the lnb was starting to fail it wouldn't regain channels it had lost...but have a feeling I'm going to be educated.

 

[Topper]

The set up in my apartment has been playing up for a while. Over the Summer months I lost quite a few channels and put it down to the heat starting to kill the lnb. Now some have come back, but then start to drift away late afternoon and by nightfall gone altogether. I'd have imagined if the lnb was starting to fail it wouldn't regain channels it had lost...but have a feeling I'm going to be educated.

Well, as nobody else has had a stab I may as well have a guess, based upon a previous post by someone in Spain. The fact that your lnb is the incorrect type is possibly not helping, because it is has a plastic cover which at specific times in the year will be stupidly hot from the sun being in the position where is is focussed back onto the lnb cover. I am wondering if the plastic has in fact been fried and cracked or damaged so is now open at some point and a spider has nested inside, only returning to the nest when the sun goes down, as I say it is just a guess but based on a previous occurrence of similar symptoms submitted by someone in Spain.

 

[jeallen01]

The set up in my apartment has been playing up for a while. Over the Summer months I lost quite a few channels and put it down to the heat starting to kill the lnb. Now some have come back, but then start to drift away late afternoon and by nightfall gone altogether. I'd have imagined if the lnb was starting to fail it wouldn't regain channels it had lost...but have a feeling I'm going to be educated.

Sounds like it could be temperature-related instability in the frequency of the local oscillator in the LNB - in which case it would be a good time to buy a new one!

PS: somewhat surprised that no-one else has raised this possibility before.

 

[Analoguesat]

+1 for heat related issues with the internal oscillators inside the lnb electronics. A while back Spanish members were reporting having to replace their lnb's every couple of years - the insane summer heat was frying the electronics

 

[Topper]

+1 for heat related issues with the internal oscillators inside the lnb electronics. A while back Spanish members were reporting having to replace their lnb's every couple of years - the insane summer heat was frying the electronics

Well yes, that is well known for all hot countries but that does not explain how it is repairing itself and then completely shutting down in the cooler evenings