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Problem of missing Astra TV channels

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poquelin
Ex Member


Oct 1st, 2008 at 12:53pm  
Hi everybody.
First, sorry if my english is not very good (I'm french, nobody's perfect!)
I have a problem with my receiver Drembox500s. When I scan the transponders of astra 19,2E, there are some channels missing. I noticed that the missing channels are those corresponding with the low and the highest (most of all) transponder frequencies.
I have a 60 cm satellite antenna with a single universal LNB. Another precision, I am a customer of french tv C+ and CSAT, and when I use the original receiver with the same antenna and LNB, I have all the channels expected.
I read that the Dreambox 500s need a good signal to work fine.
Question?:do you think it's a problem of the DM500 or my antenna may be to small? Is my LNB going wrong?
Thank you for your help.
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« Last Edit: Oct 1st, 2008 at 4:04pm by Eric Johnston »  
 
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Eric Johnston
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Reply #1 - Oct 1st, 2008 at 1:21pm  
Moisture in the cable will cause the highest frequency in the cable carriers to be affected first.  These carriers will have cable frequencies towards the upper end of the range 950 - 2150 MHz.

The universal LNB has switchable (22kHz tone) local oscillators at 9750 and 10600 MHz.  When operating on low band the satellite carriers that will come in at the upper end of the range 950 - 2150 MHz will have satellite frequencies below 11700 or 11900 MHz.   When operating on high band (22kHz tone ON) the satellite carriers that will come in at the upper end of the range 950 - 2150 MHz will have satellite frequencies below 12750 MHz.

If your missing carriers are just below 11700 or 11900 and 12750 MHz then moisture in the cable is a probable explanation.

Try manually tuning to the bad carriers to see if you get a poor quality.

Best regards, Eric.
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poquelin
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Reply #2 - Oct 1st, 2008 at 3:01pm  
First, thanks for your help.
I tried to put a lot of different images on my dreambox (gemini, nabilo, pli, dvbcrypt....) and only with one of them (PLI GARNET, but why?) the scan can detect more channels, particularly those who are missing usually. But I don't have any picture for those channels ("service could not be found"). Then i can see the snr and ber % which are about 50-70% for snr and a moving value for BER (i repeat, it's only for the channels on high and low frequencies transponder, for the other transponders it's good about 90%SNR and no BER).
So how can I check if it's a problem of moisture on the cable? have I to change the cable? the LNB?
Thank you again for your precious help, this problem is driving me crazy for more than a month now!!!!!
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Eric Johnston
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Reply #3 - Oct 1st, 2008 at 3:56pm  
I don't understand what you mean by "i repeat, it's only for the channels on high and low frequencies transponder"

Write out an exact list of the missing channels and their frequencies and polarisations.   Then subtract the LNB local oscillator frequency and see if the resulting L band frequencies in the cable all fall at the top end of 950-2150 MHz.  If so then moisture in the cable is the probably cause.  If the missing carriers are all in one band then the 13/19 supply voltages are the problem, or the LNB.  If they are all on one polarisation then the 22 kHz tone or the LNB is the problem.

If it looks like the problem is with the highest frequencies in the cable, starting at 2150 MHz and back  downwards, try a new cable.  If the F pin is not clean bright copper then it has corroded and the corrosion may have spread several feet down the cable.  I've seen aluminium film outer conductor turned to white powder for ten feet.  Use a length of centre pin wire to gently poke into the LNB socket 10 times to clean the contact springs inside.  A smear of silicone electronic contact grease is good on the new pin as this seals oxygen away from actual point of contact.  The outer of the plug must be well sealed against water or you need expensive axial crimp watertight F connectors which are rare, as are the crimp tools to close them.

Best regards, Eric.
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« Last Edit: Oct 2nd, 2008 at 8:20am by Admin1 »  
 
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poquelin
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Reply #4 - Oct 2nd, 2008 at 12:47pm  
Hi Eric
I checked all the transponders signal i have on my receiver dreambox 500s and i saw 39 transponders which are giving bad signals for a total of 79 transponders found on astra 19.2E. Below i wrote you the list of the transponders with the level of SNR AGC and BER : (I apologize for the presentation, I tried to do my best)

Transponders   
(MHz/Syms/H or V)  SNR%          AGC%        BER
11317/22000/V                   61                 80           15420
11361/22000/H              75                 93           30000
11435/22000/H              62     80                          0
11479/22000/H              61     80                          0
11508/22000/V              60     80                          0
11538/22000/V              61     80                          0
11567/22000/V              61     80                          0
11597/22000/V              61     80                          0
11670/22000/H              75     92                      16448
11685/22000/V              61     80                       49344
11914/27500/H              90     87                       20000
12168/27500/V              59     71                       3084
12187/27500/H              75     88                      60000
12207/27500/V              59     71                        8224
12246/27500/V              59     71                        8224
12265/27500/H              89     89                      15000
12285/27500/V              59     71                       24672
12304/27500/H              90     89                       12000
12324/27500/V              59     71                         2056
12363/27500/V              59     71                        40092
12402/27500/V              59     71                        23644
12441/27500/V              59     71                         5140
12480/27500/V              59     71                         39064
12515/22000/H              66     92                        16448
12522/22000/V              59     72                        16464
12544/22000/H              66     92                            0
12551/22000/V              59     72                          8224
12574/22000/H              66     92                          8224
12581/22000/V              59     72                          8224
12603/22000/H              66     92                          8224
12610/22000/V              60      72                         8224
12633/22000/H              66      92                           0
12640/22000/V              59      72                           0
12662/22000/H              66      92                         8224
12669/22000/V              59      73                           0
12692/22000/H              66      92                         8224
12699/22000/V              59      72                           0
12721/22000/V              66      92                           0
12728/22000/V              59      73                        8224

For all the 40 others frequencies, the signals are good, no BER and SNR and AGC are at least at 90%.
What do you think about that?
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