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Topic # 60545 27-Apr-2010 20:47
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Tonight, between 7pm and 7.30pm, during quite heavy rain, the picture from our MySkyHDi decoder was interrupted on and off for at least 10 minutes and loss of signal notices were displayed. Since then, the picture is back OK as normal.

I phoned SKY who explained that the weather is beyond their control and that signal loss can happen during bad weather.

I thought that the satellite dishes had been improved, particularly when you get MySkyHDi installed, so I was a bit disappointed that the signal was lost for as long as 10 minutes.

Is it still quite common and acceptable that signal is lost during bad weather? Could the satellite dish be slightly out of alignment? Have many other users experienced rain fade lately?

Thanks for your advice.

Fred 


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  Reply # 323900 27-Apr-2010 21:31
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Yes it happens to me too in very bad rain. the dish gets fulled up and the lnb cannot get the signal. the only way to stop this is a bigger dish




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  Reply # 324012 28-Apr-2010 08:50
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Yes it happens to me too in very bad rain. the dish gets fulled up and the lnb cannot get the signal. the only way to stop this is a bigger dish


This is totally incorrect, rain fade is a result of attenuation imposed by the rain droplets themselves in the path of the signal, nothing to do with the water in the dish.

Since the move from Optus B1 to D1 the power levels of both Sky and FreeView satellite have improved some 2-3dB which is a significant margin in satellite terms, however if the rain density is high enough you will still experience rain fade. Even with a 90cm dish I had at the old house, if it was really heavy rain there would still be some outage, just not as long as with the standard 64cm dish.

Cyril

Edit I should add that if you were to pour water into the bowl of the dish you will experience a signal reduction, but normally only very slight compared to what happens in the 1-2km of rain that the signal passes through on the way to the dish. A primary mechanisim is the size of the droplets is close to the wavelength of the 12GHz signal, this causes teh high attenuation. Rain fade is frequency dependant for this reason, yet the Ku band is the current band of choice.

Cyril

 
 
 
 


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  Reply # 324031 28-Apr-2010 09:15
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Quite correct, even if the dish is completely dry you will still see rain fade if there is high levels of precipitation in the signal path.

You can get hydrophobic coatings to put on dishes but since the problem as already stated is primarily elsewhere they will have little effect. These may be of some use to prevent icing however.



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  Reply # 324118 28-Apr-2010 11:56
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cyril7:
Yes it happens to me too in very bad rain. the dish gets fulled up and the lnb cannot get the signal. the only way to stop this is a bigger dish


This is totally incorrect, rain fade is a result of attenuation imposed by the rain droplets themselves in the path of the signal, nothing to do with the water in the dish.

Since the move from Optus B1 to D1 the power levels of both Sky and FreeView satellite have improved some 2-3dB which is a significant margin in satellite terms, however if the rain density is high enough you will still experience rain fade. Even with a 90cm dish I had at the old house, if it was really heavy rain there would still be some outage, just not as long as with the standard 64cm dish.

Cyril

Edit I should add that if you were to pour water into the bowl of the dish you will experience a signal reduction, but normally only very slight compared to what happens in the 1-2km of rain that the signal passes through on the way to the dish. A primary mechanisim is the size of the droplets is close to the wavelength of the 12GHz signal, this causes teh high attenuation. Rain fade is frequency dependant for this reason, yet the Ku band is the current band of choice.

Cyril



Thanks very much for your replies. I have the standard sized dish, but SKY say they don't install the 90cm dish unless it's really necessary. Based on where I live, SKY say the 90cm dish wouldn't be any better than the 60cm dish, and is unlikely to improve any loss of signal due to rain fade. SKY offered to check my dish, but said this will cost me $40 if they find nothing is wrong with it.

Therefore, if I want a larger dish, SKY told me that I would have to buy one privately and pay to have it installed myself. Do you think it would be worthwhile doing this? Does a larger dish deliver a noticeable improvement in picture quality?

 

They also said that if the dish was out of alignment, I would have reception problems all the time, and not just when it's raining, and I guess that makes sense?

SKY also mentioned that heavy winds are often the cause of no-signal messages, because the wind can cause the LNB to move and lose signal.

I realise that rainfade doesn’t happen that often, and is something we must expect from time to time, but if it was a continuing problem, then I guess that Telstra Clear’s cable TV would be the only way to go!

 

Regards

Fred

http://www.spacecom.com/customer_tools/html/body_rain_fade.htm

(Article about rain fade)

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  Reply # 324125 28-Apr-2010 12:05
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Hi, you should not experience rain fade except when the rain is so hard it probably is too hard to hear the TV for the beating of rain on the roof, and that is normal. Also be aware that often the rain fade occurs before or after the worst of the rain passes you depending on how the front is approaching or passing you. sometimes 5-10minutes difference, as the signal passes through the rain at a 40deg elevation.

If you are getting more than 4-5 outages per year and only during very heavy rain, then I would say that is quite normal, and moving to a larger dish will not fix the issue, maybe reduce the time of the outage by a small amount.

If you are getting outages in only modest rain then you may have an issue

If you go into the setup menu and into the signal test menu, what levels and C/N levels are reported, today is overcast here in Welly, so it would be good to know today but ideally in a clear sky also. This will give an idea if the dish is way off.

Cyril



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  Reply # 324377 28-Apr-2010 19:41
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cyril7: Hi, you should not experience rain fade except when the rain is so hard it probably is too hard to hear the TV for the beating of rain on the roof, and that is normal. Also be aware that often the rain fade occurs before or after the worst of the rain passes you depending on how the front is approaching or passing you. sometimes 5-10minutes difference, as the signal passes through the rain at a 40deg elevation.

If you are getting more than 4-5 outages per year and only during very heavy rain, then I would say that is quite normal, and moving to a larger dish will not fix the issue, maybe reduce the time of the outage by a small amount.

If you are getting outages in only modest rain then you may have an issue

If you go into the setup menu and into the signal test menu, what levels and C/N levels are reported, today is overcast here in Welly, so it would be good to know today but ideally in a clear sky also. This will give an idea if the dish is way off.

Cyril


Thanks very much Cyril for this advice. The signal strength / quality readings from MySky were:

Tuner 1: 70dBuV: 12.3dB
Tuner 2: 72dBuV: 11.0dB
Tuner 3: 71dBuV: 11.6dB
Tuner 4: 72dBuV: 12.4dB

These readings were changing all the time, but the above were all taken within 15 seconds of each other.

The rain at the time certainly wasn't torrential, so I was surprised at the length of the outage.

Regards
Fred

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  Reply # 324619 29-Apr-2010 11:26
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those aren't too bad.  Once things get below 10dB, some things start getting dicy.  9 and below starts dropping out.

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  Reply # 324624 29-Apr-2010 11:36
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Hi, yes as allstar says those are not out of order, but its more common for 12-13dB to be the reported signal, but as they are not calibrated devices its hard to say, so an alignment for the last 1-2dB of C/N may be in order, but rain fade to cause cut out normally kills the signal 15dB or more in actual level, so probably not going to make a big improvement.

Cyril



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  Reply # 324659 29-Apr-2010 12:34
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cyril7: Hi, yes as allstar says those are not out of order, but its more common for 12-13dB to be the reported signal, but as they are not calibrated devices its hard to say, so an alignment for the last 1-2dB of C/N may be in order, but rain fade to cause cut out normally kills the signal 15dB or more in actual level, so probably not going to make a big improvement.

Cyril


Thanks Allstar and Cyril, I've just had another look, and on average, I'm getting in the 60s and 70s for dBuV, and between 11.0 and 12.4 for dB, so I wonder whether it's worth having the aerial system properly checked out?

Is there a minimum signal strength required for SKY to install MySky? I don’t want to experience lengthy rain fade problems if a system upgrade would help avoid this problem! (I’ve been reading the recent thread about the tree problem)!

A friend says my dish is not the most recent release, do you know if the latest type of standard dish would give an improved signal over the previous dish?

In other words, the message I am being given is that, if your signal strength isn't up to the maximum possible, then you are likely to experience more rain fade than those with better signal strength, is that correct?

When you say that an alignment for the last 1-2dB of C/N may be in order, how is this done?

Thanks for your help.
Fred
 

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  Reply # 325079 30-Apr-2010 08:38
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Hi Fred your numbers are well within Skys spec but thats not to say the dish is off by a dB or so, this last precious db or two of C/N could indicate the dish is off by only a small amount but that can cause drop outs more readily both with wind and rain.

Alignment to get the dish fully peaked requires a Field Strength Meter and preferably one with spec analyser to perform a cross pol skew alignment. PM me if you want a dish check.

Cyril



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  Reply # 325157 30-Apr-2010 10:35
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cyril7: Hi Fred your numbers are well within Skys spec but thats not to say the dish is off by a dB or so, this last precious db or two of C/N could indicate the dish is off by only a small amount but that can cause drop outs more readily both with wind and rain.

Alignment to get the dish fully peaked requires a Field Strength Meter and preferably one with spec analyser to perform a cross pol skew alignment. PM me if you want a dish check.

Cyril


Thanks Cyril, that's helpful information. If I get further rain fade problems, I think it would be worthwhile to get a detailed check done, but the HD picture is fairly good most of the time.

Regards
Fred

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