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Aquiring W6 from Iraq - problem with LinkStar

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Jan 21st, 2010 at 5:55am  
I'm having problems getting on 21.5 Eutelsat from Taji Iraq with my Via Sat/LINK STAR modem.  Here is what I have

Lat: 33.5587
LOG: 44.2414

El: 43.97
Az: 213.23
Pol: 30.23
I'm not sure about if is vertical or horizontal polarization

I have a Andrews 1.2m LFL, dish p/n 3040942
LNB: NJR2784H

I'm using a sound signal finder and on this settings the signal finder says that I've found a sattelite but the modem display as it have found NO signal from sattelite.

I'm using Via Sat/Link Star modem and I'm wondering in the lengh of the cable have something to do with receiving the signal or it if this cable have any roll in that particular. (LNB to MODEM cable).

If nothing to do with, then what might be the problem aquiring the signal and how can I fix it.

Thank you

Nenad
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« Last Edit: Feb 10th, 2010 at 6:30am by Admin1 »  
 
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Reply #1 - Jan 21st, 2010 at 8:36am  
1. Information.

Ask your service provider what is the name of the Downlink polarisation ( Horizontal or Vertical ).
Also, the configuration text line that must be typed into the modem.

The box for the LinkStar modem normally contains a large glossy quick reference installation guide.
See here: Linkstar install glossy pdf 693k bytes

There is a more substantial installation instructions manual available from your service provider.
See here:  Linkstar install manual pdf 1909k bytes

2. Linkstar modem configuration

You need to connect PC to the modem with cross over ethernet cable and establish communications. The initial modem gateway IP address is formed using the last 3 hex pairs from the MAC address, for the latest modems. e.g. 10.0.x.x 10.1.x.x. 10.2.x.x  10.3.x.x 10.4.x.x etc. Convert hex to decimal using your PC calculator start, all prog, accessories, calculator, scientific mode. Mask=255.255.255.0

Use telnet to enter the configuration text line that needs to be typed into the modem.
e.g. savebootparms -pop 0x011e0001 -c 0x530 -pcr 0x365 -f 1554410 -s 27500000 -o 1 -t –40  
You can type pconf and check that the config parameters have gone in successfully. -f is frequency, -s is symbol rate

IMPORTANT WARNING: Always power off at mains wall switch before working on the coax cable.  Never get the cables shorted or crossed over.

3. Connect the LNB.

Connect the small LNB module to the LinkStar modem receive input.
 
4. Antenna polarisation set up

First set the nominal (i.e. named) feed receive polarisation.  Vertical means that the broad faces of the LNB rectangular waveguide are on top and underneath. Do it.  The LNB is on the end of a filter arm and the arm is probably now sticking out at one side or the other. Which side does not matter, it is still vertical polarisation.  If Horizontal is the required polarisation name, then the LNB arm will need to start off either upwards or downwards.
 
Second, apply the polarisation adjustment angle.  A positive adjustment angle (e.g. +30) requires an clockwise movement, while facing towards the satellite. Put your inclinometer sideways across the LNB or BUC, then tilt the whole feed/BUC/LNB assembly in its yoke, by the exact adjustment angle.  This page dish pointing Iraq shows a picture of your LNB side arm at the approximate adjusted polarisation angle, as viewed with you standing behind the dish and facing forwards towards the satellite in the sky.  Obviously you must know the name (and enter it using the web page radio button) of the polarisation you want.
 
5. Finding the satellite

Set the beam elevation using the elevation scale on the bracket behind the dish.  
 
Swing the dish boldly sideways around the approx compass azimuth and the RX LED will lock up on the satellite on the first sweep, unless the dish is sagging down a bit, in which case add a couple of elevation degrees.   Initially the RX LED will go to slow green flashing.  The centre of the beam is half way between the points where the LED drops out.  Adjust up/down and sideways.
 
As you tighten the antenna, keep readjusting to the peak.  Read the QPSK BER by typing tcmp at least 30 times (possibly 50 times !).  Get it down below 0.00009 if you can.  Spend at least 30 minutes peaking up.

6.  Transmit cable and site commissioning

Power off at the mains wall switch and connect up the TX cable.  RX LED will go slow flashing green, fast flashing green and solid green.  Don't interrupt this process.  Talk to the hub while they test your cross-pol isolation.  You may have to get yourself under the feed arm and reach up to rotate your feed polarisation a degree or two either way as they talk to you.  Be very patient between any movements; it takes the hub time to test for your x-pol null.  
 
Your modem will reboot and end up with new gateway IP address and subnet mask, ready for use.  Your service provider will tell you what are the operational gateway IP address and subnet mask.

Best regards, Eric.
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« Last Edit: Jan 26th, 2010 at 5:19pm by Admin1 »  
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Reply #2 - Jan 26th, 2010 at 12:22pm  
Very good guide!!! Especcially the remark about turning the terminal OFF before working on the cables. I've seen it go bad quite some times.

Few remarks:
2. -t = TX power at boot. This value should be set based on LBC (Link budget calculation) in 0.5 dB increments. If set too high you mights cause BUC saturation.

3. Instead op doing the TCMP command 30 times. Just do the "rep tcmp" command. This will automatically repeat the command every few seconds. To abort just type any command.

6. SAT LED status changes at following stages:
- slow flash = Modem is in RX sync mode. SW and FW are being upgrades if required.
In this stage you will be requested by the Hub to power the modem down, connect the TX cable and power the modem back up. After that either they will bring up a CW to perform the CPI test or the installer will have to bring up the CW.
- Fast flash = Modem acquiring TX synch. If succesfull the led will turn constant green.
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Reply #3 - Jan 26th, 2010 at 5:25pm  
That is a good point about not setting the initial modem transmit power too high.  

The modem output can be set from -30 dBm to -5 dBm.
A typical BUC saturates with input level of -20 dBm.
So it is not too difficult to accidentally start in saturation (and thus not get through to the hub due to distortion) or even damage the BUC.

The config value is in 0.5 dB steps, so if you input -t -20 it makes the output -10 dBm.  For safety I've amended the example in the previous post to -t -40 which means modem output = -20 dBm, so as to be safe even with the shortest transmit coax cable.  The low transmit level is -t -60 which means -30 dBm modem output level.

Best regards, Eric.
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Reply #4 - Jan 30th, 2010 at 10:26am  
hello everybody and thanks for your advices...

In the last 3 days I've been trying to find the satellite but I could not find it.  I called my service provider and I was told that the download polarization was vertical and then send me the parameters to configurate the modem:
savebootparms -pop 0x1360058 -c 0x1ffc -prc 0x365 -f 1616660 -s 27500000 -0 1 -t -30

and I ckecked with the command pconf and the configuration was succesfully updated.

But I know that in previous tries, before I found this forum (wich is very good and helpfull) I did not follow the rule about switching places with the coax cables RX and TX. I was shuting down the modem before doing this.

I switched the places of the cables a couple of times and the modem was working again.

Now when I turn on the modem, all 4 lights goes on and after +- 30 seconds, the ALARM (red) light and the SAT light goes off.

Question:  I'm wondering if  I damaged the modem and how can I figure out or test if I actually damage it by switching the cables RX in TX and opposite?

thank you very much for your all you guys have done for me, and I appreciate your help with this question...

Nenad
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Reply #5 - Jan 30th, 2010 at 10:32am  
I one more thing..I want to let you know that the leinght of my coax cable is 70 ft and 10 in... let me know if I need to change something. My cable is kind of old and can't see the markings but maybe the lengh can tell what kind of cable is it

thanks again
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Reply #6 - Jan 30th, 2010 at 11:24am  
I repeat the warning above:

IMPORTANT WARNING: Always power off at mains wall switch before working on the coax cables.  Never get the cables shorted or crossed over.

You must not "switching the cables RX in TX and opposite".   It tends to burn out the LNB power feed after brief delay. The small receive LNB module must be connected to the modem receive RX IN only.   The transmit BUC module must be connected (later) to the modem transmit TX OUT only. Never cross over the cables or get the centre wires shorted to ground (cable outers).

Start with just one cable connected between the LNB and the modem receive in RX IN.  Do all your pointing with just the one (receive) cable connected.  Find the satellite and adjust pointing for minimum bit error rate.

Possibly your modem is damaged.  If you want to test, and have a DC voltmeter then set the voltmeter to DC volts and range say 25 volts or 100 volts. DO NOT SELECT A CURRENT (AMPS) RANGE.  Apply the voltmeter to the receive LNB IN socket on the modem, taking great care not to short circuit the centre wire to the outer ring.  You may need a suitable length of wire to go in the centre hole. BE VERY CAREFUL.  If there is a voltage like +12, 13, 18 or 20V , your modem is probably OK.  The test may alternatively be made at the end of the LNB cable, but take great care about avoiding a short circuit.  If no voltage then something is burned out inside and the modem needs repairing.

Your configuration string contains an error.  The -0 1 should read -o 1  Use letter o not number 0.  The effect of command -o 1 is to turn the internal transmit power supply ON and feed power up the Transmit TX cable. -o 0 turns it off and -o 2 turns the internal transmit power supply off and allows you to use a higher power external power supply to power the BUC. Read the installation manual mentioned in previous post above.

Have you set the polarisation angle and adjusted it ? If your downlink polarisation is vertical start with the LNB arm sticking out on the left side, as viewed with you standing behind the dish and facing forwards towards the satellite in the sky.  Then adjust the feed system +30.23 deg clockwise, as viewed with you standing behind the dish and facing forwards towards the satellite in the sky.

Does anyone reading this have experience repairing Linkstar modems with burned out power feed to the LNB connector ?

Don't worry about the length of your 70 ft cable.  That is fine, even for thin coax. The longer the cable, the higher its DC resistance and the less likelyhood of damage to the LNB power feed ! Read about cable lengths in the manual referred to above.  Over 100 ft to 250ft  thicker cable is recommended.

Best regards, Eric.
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Reply #7 - Feb 10th, 2010 at 4:47am  
Hello everyone

I would like first to thank all of you for your valuable help during the last couple of weeks.  I have succeeded to find the satellite 7 degreas higher from the required elevation and the modem is finally working properly.  

The SAT LED is stays solid green.

But I still have a couple of questions Wink and i really appreciate your help.

After I type rep tcmp  the QPSK BER is changing on every second or third time from 0.0000129.. to 0.0000357..after 0.0000237 and in so on, But the readings are never going above 0.0003.... Why is this happenings and how can I fix this problem?

That is my question FOR NOW Smiley, and again thanks to you all and specially Eric, thanks again..

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« Last Edit: Feb 10th, 2010 at 6:29am by Admin1 »  
 
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Reply #8 - Feb 10th, 2010 at 6:18am  
The QPSKBER is a indication of the raw bit error rate at the input to the forward error correction system.  The errors occur randomly, due to thermal noise.

If you measure over short periods there are significant variations in the number of errors recorded from one measurement period to the next.  If you measure over longer periods the short term variability tends to average out.

With a QPSK BER under 0.0003 you have up to 3 bit errors in 10000 bits and you may be reassured that after FEC you have no errors at all. You do not have a problem and there is nothing to fix. Your system is working well.

Best regards, Eric.
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