Rain interference

JimG

I lost signal during heavy rain last night.

What's going on when this happens?
Is it that the water on the dish interferes with the reflection of the signal onto the LNB, or is that the volume of water in the air blocks out some or all of the signal coming to the dish? Or is it something else? (A local installer told me that the rain "washes the signal down to the ground")

What can be done to minimise or this problem or prevent it altogether?

Hagar

JimG wrote:

"washes the signal down to the ground"

You can use this to your advantage with a dual LNB setup.
Run a second coax from the unused connector on the LNB to your freshwater drain leaving about 10cm of the core bare in contact with the water. This will pick up the signal lost as a result of the rainfall. You should once again have a perfect picture.*


*or this may be utter tripe

Sponge Bob

JimG wrote:

(A local installer told me that the rain "washes the signal down to the ground")

Get him to install a second dish pointing at the ground below the first dish .

Tell him to phase it in with the first and then recombine the signal cables so that you get both the inadequate direct signal and the hydromorphic backscatter he was referring to and can build a proper picture from both on your Digibox .

stag39

not being too cheeky.... use an umbrella!! or put a drainage hole in it;)

Sponge Bob

stag39 wrote:

not being too cheeky.... use an umbrella!! or put a drainage hole in it;)

Will an umbrella pick up SKY ???

Ulsterman 1690

I can see Belfast Lough from the roof of my house.
If I point the dish at the sea instead of up towards the sky will the hydromorphic backscatter enable me to recieve very weak satellite signals since the surface area of Belfast lough is obviously millions of times greater than the surface area of my dish ?:D

Tony

JimG wrote:

I lost signal during heavy rain last night.

What's going on when this happens?
Is it that the water on the dish interferes with the reflection of the signal onto the LNB, or is that the volume of water in the air blocks out some or all of the signal coming to the dish? Or is it something else? (A local installer told me that the rain "washes the signal down to the ground")

What can be done to minimise or this problem or prevent it altogether?

Tell the installer to change jobs, he's a poor excuse of an installer. When its raining it attenuates or lowers the level of the signal you receive , in a well installed and maintained set up there is an inbuilt margin so that rain should not have any effect, unfortunately it is showing up a deficiency in your set up such as poor alignment.

Ulsterman 1690

Tony is spot on either your dish is too small or (much more likely) is poorly aligned

And apologies to Jim for the initial bit of mick taking but sometimes one just has to

Tony

Ulsterman 1690 wrote:

initial bit of mick taking but sometimes one just has to

your right, just done a bit myself on another thread

Gwynston

JimG wrote:

A local installer told me that the rain "washes the signal down to the ground"

:rolleyes:
This reminds me of an electrical retail assistant years ago when my father bought our first microwave oven. The spotty oik was extolling the virtues of one particular oven which had a built-in fan over another (cheaper) one. My dad asked what the fan was for and the assistant explained, "It's to help spread the microwaves around better!".

To which my dad (who has a degree in physics) retorted, "Eh? So you're telling me that if I had a lamp in the corner of a room and put a fan next to it, the light would get spread round the room better, would it?"

JimG

No problem about taking the mick, lads, that comment deserved all it got. But "Hydromorphic backscatter" is one to remember!!

Tony, thanks for the info. I have two boxes, a Pace and a Grundig, fed from a quad LNB. The signal strength on each varies between 50 and 60 percent. The signal quality is less and is worse on the Pace. Can I conclude anything from this about how my system should cope with rain?

Tony

JimG wrote:

No problem about taking the mick, lads, that comment deserved all it got. But "Hydromorphic backscatter" is one to remember!!

Tony, thanks for the info. I have two boxes, a Pace and a Grundig, fed from a quad LNB. The signal strength on each varies between 50 and 60 percent. The signal quality is less and is worse on the Pace. Can I conclude anything from this about how my system should cope with rain?

well the quality and strength are only relatively accurate so I would say dish alignment is the culprit unless you have either an obstruction such as a tree or very poor cable.

Sponge Bob

JimG wrote:

But "Hydromorphic backscatter" is one to remember!!

/me is quite proud of that one .

Dish too small or misaligned or BOTH . If you are in the NW a 60cm is a minimum size really . I have an 80cm on the west coast and had a perfect picture last night as the rain lashed against me window . My 'signal levels' on a Panasonic Digobox are typically same as yours .

As your installer is a muppet maybe you had better learn to deal with it yourself.

Myy dish is generic not a sky supplied one so I bought an Invacom 0.3db Quad with it . Your quad may not be the absolute dogs in terms of SNR .....some of the SKY ones are cheap 0.6 or 0.8db but you could read the model number off it and tell us before we comment any further

JimG

I'm in the North West indeed, though not quite as far west as you, Sponge Bob. The quad model number will have to wait until tomorrow.

Sponge Bob

The reason I asked is that a person could fit a quad themselves quite easily without touching the rest of the dish and that may be all you need if its a 4 or 5 days a year problem.

Decent quads about €25 on Ebay . Less than callout charge.

watty

If the dish is misaligned (very very likely) a Quad won't help.

Sometimes LNB rotation is very bad. Skew. Affects quality more than then level.

Zaphod

[1] AKA "Ah bollox, it's f**king raining again"

andrew3

Actually its probably more likely that the seal on the LNB weather cap has failed allowing water to ingress into the wave guide - try a new LNB - 0.7db or less SNR (signal to noise ratio)

I got a few instances were the LNB had a crack in the cap -signal went out in rain, dewy morinings etc..

watty

It's an absolute Noise figure.Not S/N (SNR).

A condom is a temporary repair. Long ago* BBC used them on small waveguide horns on OB dishes to keep rain "out of the plumbing". At that time you couldn't buy them here so I believe some BBC engineers kept the RTE OB engineers supplied.

*maybe they still do.


I replaced an LNB cap with impact adhesive and disc cut from lid of marge tub. A stretch of self amalgamating tape round edge after glue well set.

Tony

andrew3 wrote:

Actually its probably more likely that the seal on the LNB weather cap has failed allowing water to ingress into the wave guide - try a new LNB - 0.7db or less SNR (signal to noise ratio)

I got a few instances were the LNB had a crack in the cap -signal went out in rain, dewy morinings etc..

if this was the case surely the lnb would fail over time, the OP says it only happens when it rains, still sounds like alignment to me.

Sponge Bob

alignment or sensitivity or both.The LNB could have skewed a bit off the c.23 degrees right alignment if the cables were tight at the bottom and pulling it vertical . If that is a the case a check to see if it twists easily in its holder would be in order. Then it can be twisted properly , c 23 degrees right, (hopefully) and tightened in its holder .

Ulsterman 1690

A condom is a temporary repair. Long ago* BBC used them on small waveguide horns on OB dishes to keep rain "out of the plumbing". At that time you couldn't buy them here so I believe some BBC engineers kept the RTE OB engineers supplied.

ROTFL

Rippy

watty wrote:

A condom is a temporary repair. Long ago* BBC used them on small waveguide horns on OB dishes to keep rain "out of the plumbing". At that time you couldn't buy them here so I believe some BBC engineers kept the RTE OB engineers supplied.

*maybe they still do.

.

Featherlite for sensitivity would have to be worth 0.2db

lawhec

Ulsterman 1690 wrote:

I can see Belfast Lough from the roof of my house.
If I point the dish at the sea instead of up towards the sky will the hydromorphic backscatter enable me to recieve very weak satellite signals since the surface area of Belfast lough is obviously millions of times greater than the surface area of my dish ?:D

That idea isn't as far fetched as it sounds - I remember hearing back in the analogue days of a group of houses who could not get Sky reliably despite a perfectly clear view in the sky - it turned out that they were near a council dump and the metal on the site was reflecting the Astra 1 signals onto the dish, causing destructive interference! Shielding the dishes from the stray signals cured the problem.

JimG

I think this thread has been very productive! It produced a new term for the scientific vocabulary ("hydromorphic backscatter") and it managed to associate a db rating with condoms!!

Seriously though I think my problem must be misalignment. The lnb is new and the cable is good. When the system was installed first, four years ago, there was no problem. Then later on rain began to affect the signal.
Just before this Christmas I got a quad lnb installed and the installer did adjust the dish at that time (the new quad, or the installing of it, had pulled the dish out of position - somebody mentioned in another thread that this can happen). I suppose I'll have to get him to adjust it again, or get someone else. (I could tell more stories about him!) I'm not as agile myself as I used to be.

Thanks for all the suggestions. And thanks for the laughs!!

andrew3

Tony wrote:

if this was the case surely the lnb would fail over time, the OP says it only happens when it rains, still sounds like alignment to me.

I had an old 1.1db LNB from a uniden astra reciever - the weather cap broke off it and everytime a little bit of water got in (dewy mornings, rain, snow) - the reception ended up with tons of speckles - and as we know with digital there isn't much give and take!

(I tried everything - even melting the top of a pringles can into the feed horn!

plastic bags, vasaline.....(best soln - just cough up the 10euro for a new one!)

but hey I could be wrong! - check the signal strength on the box if its low when the weathers good the chances are that the treshold is too low!

andrew3

watty wrote:

It's an absolute Noise figure.Not S/N (SNR).

Thanks Watty (-if my lecturers heard that they'd kill me!)