Whats a good BER reading

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#1
hi guys,recently i purchased a satlook lite and im finding it a bit confusing to use as i dont understand the BER and what is an acceptable reading and whats not,for the last few years i have used a reciever and a small tv to tune the sats in and never had to take bit error rates into account so if any one could give a few examples of what i should be trying to get on the meter or can point out a general guide,a dummys version preferably that one be great,also once i get a lock on a transponder the scale changes from rf to db and ber,i know the higher db the better but will any signal even a small one ie 2db be enough to recieve a signal given that the meter is already locked on that transponder,if anyone has any ideas or has experience with this model they might share their thoughts with me,regards
 

satelliteman

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#2
BER, (Bit error rate), measured on most meters pre and post – Viterbi, also labeled as CBER and VBER or bBER and aBER. A reading of 2e-4 is the absolute minimum post – Viterbi measurement you should be achieving. Any worse will exceed the ability of the Reed Solomon error correction.

The Satlook G2 for example shows one BER measurement, which is pre– Viterbi / bBER.

MER, Modulation error ratio is the relation between the average signal power and the average power of noise present in the constellation.
MER for QPSK MPEG2 minimum 9dB, typical 12dB for 2/3 FEC, minimum 13dB, typical 16dB for 5/6 FEC.

SNR measurments, FEC Rate 1/2 = Threshold rate 3.6 dB, FEC Rate 2/3 = Threshold rate 4.2 dB, FEC Rate 3/4 = Threshold rate 4.9 dB, FEC Rate 5/6 = Threshold rate 5.2 dB, FEC Rate 7/8 = Threshold rate 8.2 dB

Signal power / dB, typically measured as dBuV, minimum 52dBuV, maximum 78dBuV.


Some of the above copied over from my Blog

See also: this post

..and further reading _http://www.webopedia.com/TERM/B/BER.html
 
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#3
thanks for the reply satellite man but im none the wiser,what i need is a BER dummys handbook,not that there is one but i need a simpler explanation as i find the science of it is a pain in the you know what, when you say '2e-4 is the absolute minimum'. on 5e which is always good,ie never got any picture break up, my readings with the satlook lite are 'S 10.2db, ber 1.7e-03 and on 13e my readings are S 9.2db and BER 4.oe-05,my question is are the readings im getting from 13e a better result,sorryfor my ignorence and the questions but i must get a handle on this issue,regards
 

BlindFaith

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#4
Signal power / dB, typically measured as dBuV
dBm is typical for satellite (easily converted to dBuV for known impedance)
 

wod

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#5
my horizon meter has ber measurement and I always tune for the lowest reading but highest db signal reading.
 

BlindFaith

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#6
minterno said:
thanks for the reply satellite man but im none the wiser,what i need is a BER dummys handbook,not that there is one but i need a simpler explanation as i find the science of it is a pain in the you know what, when you say '2e-4 is the absolute minimum'. on 5e which is always good,ie never got any picture break up, my readings with the satlook lite are 'S 10.2db, ber 1.7e-03 and on 13e my readings are S 9.2db and BER 4.oe-05,my question is are the readings im getting from 13e a better result,sorryfor my ignorence and the questions but i must get a handle on this issue,regards
..as @satelliteman wrote, you have to differentiate between before and after Viterbi. After viterbi a BER = 2x10-4 is needed for quasi error free transmission. Quasi-Error-Free (QEF) means less than one uncorrected error event per hour, corresponding to BER = 10-10 to 10-11 at the input of the MPEG-2 demultiplexer.
 

Huevos

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#7
minterno said:
what i need is a BER dummys handbook,not that there is one but i need a simpler explanation as i find the science of it is a pain in the you know what, when you say '2e-4 is the absolute minimum'.
Well it is pretty simple really. You want as few errors as possible before you try to correct them.

First here are what the numbers mean. At the start there is a number between 1 and 9, (2 in your example above) followed by "E-" and then another number (4 in your example). The first number is the number of errors and the second number is the size of the sample. So:

  • E-2 = 100
  • E-3 = 1000
  • E-4 = 10000
  • E-5 = 100000
  • E-6 = 1000000
  • E-7 = 10000000
  • E-8 = 100000000

so in your example "2E-4", the "E-4" part means we are looking at a string of data containing 10000 bits, and the "2" part means there are 2 errors. That means there is 1 error in every 5000 bits sent. An error of that amount is correctable. Look at another example though, "9E-2", that is 9 errors in a data string of 100 bits, or 1 error in 11 bits sent. Such a high error rate is impossible to correct.

Anyway enough of that because it is not very user friendly. If your meter has MER that is the best indicator of the health of the received signal, and you want the highest number possible. Satelliteman's figures are pretty conservative (i.e. give a good weather margin) and you can get away with much worse, for example 8dB will give an error free picture on an FEC 5/6 source, but the first drip of rain and you will lose the picture.
 
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#8
thanks for the replys satelliteman,Blindfaith,Wod,and Huevos,that makes it all a lot clearer,i will still have to digest it a little but that def helps,thanks guys
 

vma

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#9
You might want to take a look at this very good serminar in PowerPoint format. It explains all there is about BER and MER and why you should measure BOTH!

Link: _http://www.rian-bv.eu/files/1264428964_MERBERSEMINAR_011025REV.PPT

Cheers,
vma
 

satelliteman

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#10
Very informative, thanks vma ;)
 
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