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| SatSig Topics Index › iDirect Forum: hubs and terminals › iDirect 3000 series router problem |
SatSig topic: iDirect 3000 series router problem(Read 23991 times) |
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Mar 28th, 2009 at 1:01am
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Mar 28th, 2009 at 11:39am
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Mar 28th, 2009 at 3:41pm
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Mar 28th, 2009 at 7:57pm
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Mar 28th, 2009 at 8:00pm
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Mar 28th, 2009 at 8:33pm
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Mar 31st, 2009 at 3:11am
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Mar 31st, 2009 at 11:51am
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Apr 1st, 2009 at 5:45am
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Apr 1st, 2009 at 11:07am
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Apr 1st, 2009 at 5:06pm
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Nov 5th, 2009 at 11:30am
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Nov 5th, 2009 at 11:38am
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Nov 5th, 2009 at 12:12pm
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Nov 6th, 2009 at 10:53am
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Nov 9th, 2009 at 8:36am
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Mar 30th, 2015 at 5:34pm
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Nov 2nd, 2015 at 9:11am
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Jan 3rd, 2016 at 2:48pm
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Jan 3rd, 2016 at 6:51pm
Note the transmit power setting at the remote and the spectrum analyser level, write them down, about halfway down the paper page. Decrease the remote site power level by 1 dB and repeat the hub spectrum analyser measurement. Repeat this several times. Write down each pair of measurements, lower down the page. If you are obviously in the linear portion of the curve then go up in level cautiously. Keep increasing the remote transmit power setting and you will find that each 1 dB step up at the remote no longer causes a 1 dB step up in the measured signal at the hub. The BUC is starting to be overloaded and the signal is becoming distorted. Plot the measurments on graph paper and draw a straight line through the linear part of the curve. Look at the vertical gap between the straight line and the top part of the curve where compression is starting to occur. Once the spectrum analyser measured level is 1 dB behind the input level into the BUC, you have reached the -1dB gain compression point of the BUC. Don't go any higher. Record the remote modem power setting and make sure the hub never tells the remote to go above this value during rain, for example. The normal, clear sky, operating power will typically be about 6 dB below the -1dB compression point. Set the final clear sky level to give the required Eb/No at the hub as specified in your system design. Hubs may well do this automatically so that all incoming TDMA bursts are at the same level as far as possible.. The -1 dB gain compression point is where the black double ended arrow is 1 dB long. In this case the -1 dB compression point is where the transmit power setting is -18 dBm. The actual BUC capability is +4 dBW at its -1dB compression point. This "2 watt" BUC2 is actually able to put out 2.5 watt. Regarding the remote modem power setting this might be -12 dBm with a cross site cable loss of -6 dB. If you exceed the -1 dB compression point the power increases slightly further but the signal pulse shape deteriorates and the error rate increases. Also, you start to cause interference to the adjacent frequency customers and damage your BUC with high voltage spikes which may cause gradual deterioraion or sudden failure. If you are using a higher order modulation method like 8PSK or 16QAM you should operate below the -1 dB compression point, say -1.5 dB or further down, as these modulation methods have high error rate if distorted. If you are ever faced with a problem where a remote is believed to be transmitting but nothing is being received at the hub, try reducing the remote power in 5 dB steps. If a BUC is grossly overdriven the signal is so distorted it cannot be received at all by the hub TDMA receiver. If you are transmtting multiple carriers, typically from a teleport hub, you need to operate your BUC or HPA backed off even more so that intermodulation product interference is down at an acceptable level. Read the BUC/HPA manual about the curve for input and output back off for multicarrier operation. e.g. -4.5 dB input back off. Two equal carriers, would each be at -7.5 dB input back off maximum. Best regards, Eric. |
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Jan 3rd, 2016 at 8:33pm
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Email me:eric@satsig.net |