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Idirect 3000 Tx power

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Apr 7th, 2010 at 10:24am  
i am using idirect 3000 series with 1.2 dish my problem ia that my service provider inform me that i had problem
my tx power and they ask me to verify my cable and alighn my dish.
so i checked the cables and repoint the dish successfuly and my vsat can join the network very quickly with very good internet speed .but after few minutes the internet traffic stop and i had to reboot the idirect. so i try to moniter it through isite and i noticed that the TX power increase gradualy from -10dB until it reach 0dB then the internet stopped completly.
i call the service provider and they say that i had to verify the cables and dismanlte the feed horn and clean it because they suspect there is humedity inside and the vsat increase the transmit power to overcome it.so i dismantle the Feed and i clean it and but it back but the problem remain . so does any body come across such issue before . and i have to solve it because the service said they have to deactivate the vsat becuase the increasment of the transmition power can damage my equinments
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Eric Johnston
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Reply #1 - Apr 7th, 2010 at 11:01am  
If you start from a very low modem output power level, and increase it slowly, the BUC output will also increase slowly at the same rate. 1dB output increase for 1 dB imput increase. This is linear.

The receive quality at the hub TDMA receiver will also improve.

However, once the BUC has reached its rated power output (say 2 watts at -1db compression point) the quality of the receive signal at the hub will have reached its maximum.  If you increase the modem output power further the BUC output power will increase by a negligible amount and the BUC output signal will be distorted, causing the hub receiver to have high error rate and indicate low signal quality. There is also risk of damage to the BUC, particulary if the modulation is on.
...

During line up the hub should set your modem to transmit CW and increase the level till the -1 dB compression point is identified. This corresponds to your modem operating at its rated power oputput.  the hub need to plot a graph of the CW model output level and the level measured at the hub and see hwere the gain is reduced from linear by -1 dB.
Note the modem output level and set it in the hub configuration software. The hub will then never tell the remote to go above this maximum level in service.

The hub should then reduce your modem level until the correct level is being received at the hub.  Bursts from all sites need to be very similar. Normally, in clear sky your site should operate at least 6 dB below the rated power (e.g. 0.5 watt versus 2 watts) so that there is a 6 dB uplink power control range available to deal with rain fading.

In the above graph, assuming 10 dB cable loss, the clear sky modem output power might be -16 dBm and in heavy rain -10dBm (i.e. the maximum allowed and causing -20 dBm at the BUV imput socket).

Read more in Section 6 "Configuration TX Initial Power" of iDirect Technical Reference Guide iDS release 8 (3.57 Mbytes pdf file)

Best regards, Eric.
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TDMAMike
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Reply #2 - Apr 7th, 2010 at 11:19am  
If there is no moisture, then your system could be out of focus.  There is obviously a problem if the NMS is pushing you up in power until your BUC saturates.  I would guess that your problem is with Focus or you are off-peak.  I wouldnt rule out a faulty cable either.  Your bursts are arriving low at teh hub, therefore the NMS is pushing you up (to meet the desired UCP).  You need to figure out why.  My guess is you are our fo focus or off-peak. Did you get an isolation check with this system?
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Reply #3 - Apr 7th, 2010 at 12:20pm  
Thank you Eric and TDMAMike for you quick response.
you may not know that i am not expert in the Vsat technology but i have some knowledge in the Vsat installation .
so what i want to know is how to solve the issue the service provider claim that is local problem and i had to recheck the cables and they suggest that i should cut the cables and reinsert the connectors.
anther point what do you mean by out of focus and off-peak and how do i correct this
so what do you advice.
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Eric Johnston
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Reply #4 - Apr 7th, 2010 at 6:19pm  
Out of focus means your feed is not the correct distance from the lower edge of the dish (focal length).  This is typically due to using wrong length struts, wrong holes for the struts, yoke bracket wrong type or wrong way round. The feed horn should aim towards the dish, approx 1cm above the centre point.

Off peak means you are not yet aimed accurately at the satellite.  If this is your first VSAT dish then you may be totally unaware of the very precise accuracy required.  It is no good just to get an excellent receive signal. That is an inadequate test.  You must get to the exact centre of the beam, which is very difficult considering that the top of the beam is rounded. Also the receiver may show negligible change in quality once you have a really excellent signal.  

When adjusting using nuts on screws the accuracy needed is about 1/6th of a turn, or one flat on the nut.

A reliable method to peak up is to degrade the signal to exactly equal levels either side of the beam and then set mechanically to the centre by counting the turns and flats on the nuts.  This is easy in elevation where there is no backlash.  In azimuth more skill is needed.

Typically it may take you 10 minutes to find the satellite and then at least 30 minutes peaking up.  As a beginner you may spend an hour or more peaking up once you have found the satellite.  The accuracy required is very high as the transmit beam is narrower then the receive beam.

Ask the hub what is the maximum modem output power they have set (corresponding to the -1dB compression point of your BUC).

The hub can test your BUC by gradually increasing the modem CW output level from a very low level starting value and measuring the CW carrier at the hub.  Once it goes non linear and there is a -1 dB difference from straight line then stop and record  the modem output level.

The connectors on the BUC cable are critical.  The braid sheath must make good contact with the plug outer.  The centre wire pin must be clean and bright and stick out 1.5mm beyond the rim of the plug, and not push back when screwed in.  Low DC volts at the BUC, due to wire corrosion, could explain low transmit power (e.g. 0.2 watts max instead of 2 watts).  If you have a burned out wire use some clean wire (from the cable so it is the same size) to poke in the BUC to clean the contacts inside - although there may be permanent damage to the BUC springs.  A smear of silicone electronic contact grease is recommended for all installs.  The grease excludes oxygen and moisture from the microscopic contact areas where the springs and wire actually press together.

Best regards, Eric.
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Reply #5 - Apr 7th, 2010 at 7:26pm  
thank you Eric for your useful info
i followed your instructions after i remake  my cables and i spent about 45 minute picking up the signal i manage to get 17 .8 V with -13.45 dB SNR with i site
now i can see that my tx power is -13.5 dB and i decrease until it reach -17 dB .so what do you think ?.
tomorrow i will call my service provider to verify that every thing is ok.
thank for your help
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TDMAMike
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Reply #6 - Apr 8th, 2010 at 2:58am  
Your Hub Operator will determine if your cable replacements rectified the problem.  

You can probably follow along with the NMS's power offsets after acquisition  by using a few useful telnet commands..  You can follow along via telnet by toggling on remote messages by typing xon <enter>  and the turn on your remote stats by typing rmtstat <enter>.  Remote status should scroll from that point.  Turn it off with a simple xoff.

That or you can query it with an occasional tx power command.
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Regards, &&&&M
 
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