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  #1  
Old 2010-02-02 , 13:53
roberichansen roberichansen is offline
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Default Signal Quality / Strength

Can someone please help by answering the following question:

Lets say someone has a signal quality and strength of 100%. My question is this: is his quality of picture better than someone who has a signal quality and strength of only 70% (assuming perfect weather conditions).
  #2  
Old 2010-02-02 , 14:17
Geoff D Geoff D is offline
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Originally Posted by roberichansen View Post
Can someone please help by answering the following question:

Lets say someone has a signal quality and strength of 100%. My question is this: is his quality of picture better than someone who has a signal quality and strength of only 70% (assuming perfect weather conditions).
Yes it is BUT whether a viewer will see the quality difference will depend on the quality of the TVs used to view channels from each decoder.

The indicators on the decoders are not what they used to be. These days, these measurements are nothing more than signal indicators and cannot really be used to draw any conclusion about the "real" quality.

Signal strength is supposed to be an indicator of "how much" signal is received from the satellite, via the antenna, by the decoder. The higher this value, the better and the higher this value the better the decoder can do its job. And in poor weather, it means that the signal has more "margin" to deteriorate before the decoder will not be able to "lock onto" and decode the signal.

"Signal quality" is a measure of what the content quality is after the decoder has received the signal and decoded it. It is a very rough indication of the technical term Bit Error Rate (BER), the better the signal quality, the less signal distortion is present and the better the image should be on a TV set. Decoders have a " threshold BER value" below which signals cannot be accurately decoded anymore. The more complex the signal, the higher this threshold value is.
So a HD signal, with its much larger data content measured in Mega bits per second, the better the BER needs to be for proper decoding.

So a decoder with a signal value of 100% (equals the maximum value the decoder can accept) but with a BER of below about 60% is unlikely to be able to properly decode the signal and no picture will be the result.

At the same time a signal level of above 60% but with an acceptable BER may even give a "quality" measurement of 100% and still be able to decode the signal and display an acceptable picture.

What one wants is the maximum possible signal at the best quality under good weather, so that the " fade margin" is as large as possible to allow for signal deterioration in "bad weather"

Signal strength is governed by the size of the antenna, the larger the antenna the more signal level will be available. Quality is a factor of many things, including the quality of the LNB fitted into the antenna.

Hope this helps.
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Last edited by Geoff D; 2010-02-02 at 14:20. .
  #3  
Old 2010-02-02 , 14:37
roberichansen roberichansen is offline
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Thanks Geoff for that informative response.

In your view, do you think someone with a signal quality and strength of 80% (at worst, it changes on each channel) should slightly re-allign his satellite dish himself, or would he be risking his neck and already fine reception for no good reason?

Details: 60cm Metal Dish, HDPVR and 1131 XtraView, LED Full HD TV, Cape Town
  #4  
Old 2010-02-02 , 14:59
Geoff D Geoff D is offline
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Originally Posted by roberichansen View Post
Thanks Geoff for that informative response.

In your view, do you think someone with a signal quality and strength of 80% (at worst, it changes on each channel) should slightly re-allign his satellite dish himself, or would he be risking his neck and already fine reception for no good reason?

Details: 60cm Metal Dish, HDPVR and 1131 XtraView, LED Full HD TV, Cape Town
(1) Rule number 1- If it ain't broken don't fix it!
(2) You have the odds stacked against you on this one:

(a) You have the smallest antenna 60 cm, way below the recommended size of 90 cm.
(b) You are in CT, the furthest from the satellite you can get without a boat.
(c) It also means that whomever installed the antenna has probably done the best he can anyway on that front i.e. it is unlikely you will get better without a proper Field Strength Meter
(d) The 80 % "quality" is open to debate - you may be able to improve this IF there is some evidence that the LNB "skew angle" can be optimised.
(e) If you can see marked difference between say 101 and the fashion TV channel on quality and signal strength then it would suggest that skew angle adjustments are required.

(3) IF you are contemplating this because of signal drop out in bad weather, then my response is don't bother because the root cause is that toy antenna of yours!

(4) If you really want to try to optimise antenna alignment by yourself, then I can send you a DIY recipe to follow, that will ensure at least you get back to where you were before you started, not worse off. Send me a PM with your contact details and I will respond.

(5) The varying measurements from channel to channel: If this is between HOR and VER channels, then there could be something in it (but then these differences have to be fairly large) but if it is within the group of VER channels, then it is more likely related to the signal streams themselves and nothing you do will change that.
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  #5  
Old 2010-02-02 , 16:02
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Quote:
Originally Posted by Geoff D View Post
(b) You are in CT, the furthest from the satellite you can get without a boat.
Is there not DSTv on Marion island?
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  #6  
Old 2010-02-02 , 18:20
Geoff D Geoff D is offline
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Originally Posted by Theo View Post
Is there not DSTv on Marion island?
if there is then it is on C-band and you still need a boat to get there!
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  #7  
Old 2010-02-06 , 14:47
roberichansen roberichansen is offline
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Just an update on my alignment issue, thanks to the help of this forum I was able to get mostly 100% signal quality and 98% signal strength. My worst quality now is 90%, but only for some channels. As is common in these threads, I would like to thank Geoff for his help with the alignment guide.
  #8  
Old 2010-02-25 , 11:11
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Tulani Tulani is offline
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Quote:
Originally Posted by Geoff D View Post
(1) Rule number 1- If it ain't broken don't fix it!
(2) You have the odds stacked against you on this one:

(a) You have the smallest antenna 60 cm, way below the recommended size of 90 cm.
(b) You are in CT, the furthest from the satellite you can get without a boat.
(c) It also means that whomever installed the antenna has probably done the best he can anyway on that front i.e. it is unlikely you will get better without a proper Field Strength Meter
(d) The 80 % "quality" is open to debate - you may be able to improve this IF there is some evidence that the LNB "skew angle" can be optimised.
(e) If you can see marked difference between say 101 and the fashion TV channel on quality and signal strength then it would suggest that skew angle adjustments are required.

(3) IF you are contemplating this because of signal drop out in bad weather, then my response is don't bother because the root cause is that toy antenna of yours!

(4) If you really want to try to optimise antenna alignment by yourself, then I can send you a DIY recipe to follow, that will ensure at least you get back to where you were before you started, not worse off. Send me a PM with your contact details and I will respond.

(5) The varying measurements from channel to channel: If this is between HOR and VER channels, then there could be something in it (but then these differences have to be fairly large) but if it is within the group of VER channels, then it is more likely related to the signal streams themselves and nothing you do will change that.

Can not coaxial cable from LNB to decoder also be an issue? Old cable can cause signal loss. Also shorter cable lengths are better.
  #9  
Old 2010-02-25 , 13:10
Geoff D Geoff D is offline
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Originally Posted by Tulani View Post
Can not coaxial cable from LNB to decoder also be an issue? Old cable can cause signal loss. Also shorter cable lengths are better.
Yes it is possible, but then we need to explore furtehr which channels are being affected and link those to a specific transponder and yes the shorter the cable are the better.

Unfortunately, mnay users do not have much option regarding cbale lengths, especially if the installation is already in place, then one has to live with what you got.
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Spare decoders: SD PVR(2), PACE HD PVR 4T, DSD 660, 1110, 1131, Explora 1
2 unmentionable FTA decoders
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1.2m antenna, 8-way universal LNB, 2x6 MS, FSM permanently connected.
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