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is Jammer effects on KU-band  

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Mar 29th, 2010 at 8:41am  
Dear All,

There is a problem in antenna pointing with iDirect modem as it is not receiving voltages more than 5 to 6 Volts. it shows only yellow signal level and not going to the green signal levels which may be caused due to jammer in that location ... is there any effect of jammer on KU band , on the other hand C-Band link is up and running fine.

kindly suggest what to do.
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Reply #1 - Mar 29th, 2010 at 9:16am  
If the system has been working normally then:
Poor LNB connection.
Antenna mispointed due to wind, vandalism etc.
Water in the feed.
Interference from new carrier on same or opposite polarisation.

If this is a new system which has not yet worked:
Not yet pointed at the correct satellite (you have peaked up on the wrong one).
Wrong polarisation.
Wrong options file.

Best regards, Eric.
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Reply #2 - Mar 29th, 2010 at 11:01am  
Dear Eric,

All the equipments are new as this is a new installtion. antenna mispointing can be possible we will check it
i think no issue with option file.

My Question is that is Jammer effects of Ku -Band only a C-band Link is working fine what would be the issue if pointing like Elevation & Azimuth is correct ?
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Reply #3 - Mar 29th, 2010 at 11:34am  
Not yet pointed at the correct satellite: You will be able to peak up on any and all satellites but the modem won't lock, give higher voltage and go green till you have the correct satellite and correct polarisation.

Large error in polarisation angle will give the same effect as wrong satellite.

Slightly misadjusted polarisation angle will give signal lock but marginal low quality due to interference from the other polarisation.

I've just thought of another possibility, associated with new equipments.  You may have the wrong LNB.  Ku band LNBs come with a variety of local oscillator frequencies e.g. 9.75 GHz, 10 GHz, 10.6 GHz, 11.3 GHz etc.  You need the correct LNB so that the L band frequency into the modem (as in options file) + the LNB LO freq = the actual satellite downlink frequency.

Regarding possible local inteference, C band tends to be affected by WIMAX services that operate on lower inband or nearby frequencies.  Ku band is not affected by WIMAX.  Ku band may be affected by radio relay links or nearby radar systems.  For a new service I would not expect local interference/jamming to be a problem unless the local environment was obviously full of radio transmitting devices.

If you have some good reason to suspect a local jammer/interferer, then put a 3 dB splitter in the LNB cable and connect a spectrum analyser via the DC block side connector. Hold the feed horn and LNB in your hands and point it around in all directions to identify the source.

Best regards, Eric
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« Last Edit: Mar 29th, 2010 at 12:41pm by Admin1 »  
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Reply #4 - Mar 30th, 2010 at 1:36pm  
Great !!!

One thing i want to mention that we are using transreceiver so option file is correct and made after adding and we have tested it in almost 50 sites on this senerio. another thing i want to ask that if we do UAT and confirm it from satellite operator that we are on the satellite or not is it help ful .. we cannot use spectrum as this is a very remote location.

Thanks for the reply ...
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Eric Johnston
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Reply #5 - Mar 30th, 2010 at 4:45pm  
Unless the receive LED on the modem goes green the hub will not be able to control the modem and carry out any tests.  If the hub turns the main outlink carrier off then the 6 volts will drop if you are pointed at the right satellite - but they won't want to do this if there are 50 other sites in use.

Low volts is most likely due wrong satellite or polarisation.  If the elevation angle on the bracket reads correct on the scale, what volages do they see when they try pointing at the next two satellites along the orbit each way. They may alternatively be on completely the wrong satellite, a long long way away, due to some misunderstanding.  Are they looking in a plausible azimuth direction?.

Is there any chance that the the feed position is wrong, dish upside down, wrong holes in feed support arm etc.  Trees/wall/roof blocking the beam ?

Does the 5 - 6 volts appear to be associated with a satellite, or is the figure of 6 volts unchanging wherever the antenna is pointed.  Does the figure drop right down if the antenna is pointed away from any satellite ?

If the voltage is fixed and unchanging then test the LNB.  The LNB on its own might show a very low voltage if pointed up at the sky and slighly higher voltage if pointed at warm hand or the ground. If you point the LNB at a local interference source the volts should go up. Then re-attach the LNB to its filter arm.

Best regards, Eric
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Reply #6 - Mar 31st, 2010 at 9:27am  
Due to Lower Coverage area on satellite , voltages always vary and remote always try to locate the right satellite. There was no issue with the look angle (LOS) and we are pointing on satellite according to the link budget.

yes , it can be a issue of wrong polarization.

we take the frequecny from satellite operator and want to transmit the carrier but can't able to transmit what will be issue as we are receving only 6 volts maximum is this gonna transmit or not .. ?

how much sea level in meters will be prefered for iDirect link in any region / site.

i am following the steps you already mentioned earlier it will also be helpful .

Thanks Eric.
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Eric Johnston
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Reply #7 - Mar 31st, 2010 at 10:24am  
If you are located in the outer contours of the coverage beam and the voltage is too low for the modem to lock up then you need a larger dish.  1.4 times the diameter will give 3 dB improvement in dish gain.

Have you tried pointing at several other satellites along the orbit each way ? It is quite likely you are on the wrong satellite. Elevation scale may be in error by a few deg (due to clamp tightness, pole not exactly vertical and dish sag) and azimuth may be in error by several deg also due to approximations and local magnetic anomaly.

If the polarisation is wrong or not adjusted accurately, correct this.  Set the receive polarisation to the named, nominal, polarisation initially.  Then turn the feed by the calculated adjustment angle.  Positive adjustment is clockwise, as viewed with you standing behind the dish and facing forwards towards the satellite in the sky. If you use this dish pointing calculator (Iraq) it shows you a picture of what your polarisation should look like (approx). Drag the map from Iraq to any country in the world. Set polarisation to +/- 1 deg accuracy if possible and be prepared to make a few deg adjustment under verbal instruction from the hub.

The remote modem must not transmit until the modem RX has gone green and the hub can successfully send commands to it.

Height above sea level makes negligible difference to pointing angles. Ignore this.  Mountains blocking the view to the satellite do matter of course.

Best regards, Eric.
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Reply #8 - Mar 31st, 2010 at 3:41pm  
Could your LNB be the wrong LO frequency or out of tolerance? see thread "iDirect rx acq range".  It is easy to measure if you have a Spectrum Analyzer.  Simply look at the beacon, usually around 952 Mhz for Hor Recv, and see how far off frequency it appears.  The difference is the LNB LO drift + SpecAn calibration error.  Tektronix 2710 series SpecAn have been sold on EBay for cheap.  I got mine, working and in calibration for $600 US.  Hold out for one with the marker freq counter option.

John
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Eric Johnston
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Reply #9 - Mar 31st, 2010 at 6:34pm  
Get the hub to issue you with an options file with much wider acquisition range.  This is particularly applicable if you are using cheap, unstable, DRO type LNB.  PLL type LNB is recommended for low bit rate outlinks (e.g 2 Mbit/s with DVB-S2).

Best regards, Eric.

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« Last Edit: Mar 31st, 2010 at 11:09pm by Eric Johnston »  
 
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