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Upgraded system not syncing

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Oct 24th, 2010 at 11:20am  
Hello

Having troubles getting TX sync.

I'm currently in the Middle East, on the edge of the NSS6 spot beam. I have a Linkstar RCST working with a 1.2m dish with a 3W Ku BUC. I have recently installed a 2.4m dish with an NJT5017F 4W Ku BUC.
I have been transmitting through the 1.2m dish at -18 power.
I have added the external PSU to the system and enabled it via the "save -o 2" command.
When powering on the RCST, a fast blinking SAT LED is as far as I get with "NCR SYNCED" the final message.
I have aligned the new dish as best as possible and have achieved a varying BER that averages at around .0005 which is better than the 1.2m dish that averages around .0010.
I have called the NOC and they have tried raising a CW, but say they cant see me. I was told to re-align the dish however being as close as I am to the edge of the beam, I think this is as good as its going to get.

Can anyone provide some suggestions?

Thanks
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Eric Johnston
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Reply #1 - Oct 24th, 2010 at 12:39pm  
Check that dbpr bootconf shows ODUstatus = EXTERNAL
This will verify that your save -o 2 has worked

Check that tclgets shows PCRReceived TRUE
This will verify that you are aimed at the correct satellite and not some nearby satellite with a similar outlink carrier.

The symptoms point to a transmit problem. All I can suggest is some questions..

Is the transmit cable connected at each end ? The centre wires at the F plugs must be long enough to make contact inside the sockets. 1.5mm proud of the F plug rim.
The braids should make good contact.  Make sure there are no braid fragments shorting the cable.
Is the external power supply switched on ?
Does 24V appear at the BUC end of the cable ?
Does the BUC get warm ?  It should consume up to 50 watts DC power (2 amps at 24V)
The BUC will mute (block its output) if the 10 MHz reference is missing or if the local oscillator in the BUC is unlocked.
A modem output setting of -t -18 means the output power is -9 dBm.  The input to the BUC should not exceed -20 dBm, so I presume you have a fairly long cable ( approx 11 dB attenuation ).
If you have a rather short cable I would use an initial power setting more like -t -48, meaning modem power output of -24 dBm.  Your hub should have no difficulty at all (*) detecting a CW carrier of say 0.4 watts. (assumes 6 dB loss cable)
It is important not to overload the BUC.  If you do you may damage it, the DC power drawn may be excessive and your external power supply may trip OFF.
Does the whole system work normally if you substitute the old 3W BUC ?
Your 2.4m dish should be 6 dB better than a 1.2m dish.  But this will only be the case if the dish is not distorted. Put tight strings or fishing lines up/down and across the front. The strings should just touch (1mm gap max at 14 GHz). Several dB gain loss will occur if the dish is distorted due to the weight of the feed/BUC assembly.  Where there are joints in the dish panels,the surfaces should be level either side.
Is the 2.4m dish intended for Ku band operation ? A white plastic C band dish may have a poor quality wire mesh hidden in the plastic, unsuitable for 14 GHz.
Dish pointing should be peaked by moving off to equal degraded qualities either side and the mechanically centreing.  Count turns/flats on the elevation nut. Do equal winding in of both azimuth nuts after getting equal side levels by swinging sideways to rest against each nut alternately.

Changing from a 1.2m dish to 2.4m dish should improve your transmit signal by 6 dB.  Increasing the BUC power from 3 to 4 W should give a 1.25 dB improvement.

This 700k pdf installation manual http://www.satsig.net/linkstar/linkstar-vsat-rcst-installation-manual-2005.pdf has full details of troubleshooting transmit problems.
wxw

Best regards, Eric.

(*) a skilled hub operator with the right test equipment will be able to detect far lower levels of CW.
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Reply #2 - Oct 24th, 2010 at 2:27pm  
Thanks for your suggestions Eric.

I will hopefully post my resolution to the problem soon.

In the meantime can you clarify the tclgets command.

When I enter the command with the working 1.2m system I receive no "PCRReceived TRUE" message, though I do get:

PCR Interval 90 (ms)
PCR LMC Histogram - with data following.

Does this more or less mean the same thing?

When I spoke to the NOC, they remotely set up the CW. This should indicate that I'm on the right bird? Also does the remote station need to be able to transmit for the NOC to do this or do they send the commands as UDP type data like a TV signal?

Regards
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Reply #3 - Oct 24th, 2010 at 3:08pm  
I was not aware of those PCR messages. Does the data suggest it is still waiting/searching ? Does is also say 'state=NCRSync'

Did your terminal do anything at all when the hub told it to send CW ?  Can the hub try telling the modem to reset so you can see if all the LEDs flash at boot up ?

Don't transmit CW by manual command unless the NOC says so and you are certain you are on correct satellite. Use a much lower transmit power setting for safety.

May be wrong satellite.  The modem can lock to a similar symbol rate carrier on an adjacent satellte even if the centre frequency is different by up to 2 MHz or so.

Best regards, Eric.
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Reply #4 - Oct 24th, 2010 at 3:40pm  
This is from the 1.2m setup that is working.
I will run the command when we hook up our new dish during our arranged engineering period.

tclgets
TCL statistics
Linkstar IV HW
State          SORFSynced
Avg pcr error  0
Freq Error     -0.9992006 (Hz)
PCR Interval   92 (ms)
PCR - LMC Histogram
   -10 -     -1 : 202218
     0 -      9 : 385910
    10 -     19 : 196496
    20 -     29 :    167
    30 -     39 :    137
    40 -     49 :    115
    50 -     59 :    125
    60 -     69 :     98
    70 -     79 :     63
    80 -     89 :     26
DAC Histogram Center 0xe63d
  -200 -   -191 : 785150
  -190 -   -181 :     12
  -180 -   -171 :      8
  -170 -   -161 :     13
  -160 -   -151 :     12
  -150 -   -141 :      7
  -140 -   -131 :      9
  -130 -   -121 :     10
  -120 -   -111 :     12
  -110 -   -101 :      9
  -100 -    -91 :      9
   -90 -    -81 :     10
   -80 -    -71 :     13
   -70 -    -61 :      7
   -60 -    -51 :      8
   -50 -    -41 :      8
   -40 -    -31 :     11
   -30 -    -21 :     14
   -20 -    -11 :     15
   -10 -     -1 :     10
     0 -      9 :      8

pconf does confirm power set to EXTERNAL.

Regards
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Reply #5 - Oct 24th, 2010 at 4:22pm  
If you get the same receive results when receiving on the 2.4m dish then I think the problem is to do with the transmit level, external power supply, cable or BUC itself ?

Can you carry the entire 3W feed system across to the big dish ?

Best regards, Eric.
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Reply #6 - Oct 24th, 2010 at 7:04pm  
I checked the 10MHz Ref at both BUCs and results were similarly good, if anything there was less interference at the 4W BUC

I tried running the 4W BUC at -24dB incrementing it up .5dB at a time to no avail. I checked the BUC after this and it was stone cold!

I swapped the BUCs over and have been able to achieve TX sync with the 3W BUC on the 2.4m dish.

I am now playing with the power levels again to optimise the connection speed.

Eric, is there any hope for my 4W BUC? Would you deem it to be broken? If not what else could I do to test it?

Thankyou for your help Eric, it is much appreciated.

Best regards
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Reply #7 - Oct 24th, 2010 at 8:18pm  
Hello Tim,

Can you please tell us what is the model of the old BUC you had? Maybe one of them is extended Ku and the other is regular Ku for example? Maybe they dont have the same LO?

Kind Regards,
Nimrod
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Reply #8 - Oct 24th, 2010 at 8:31pm  
Hi

I considered this at one point however I failed to find any data on the BUC to check the LO f.

The 3W BUC is; P/N 1025739

Regards
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Reply #9 - Oct 24th, 2010 at 8:47pm  
Can you make sure with the NOC that the new BUC LO is ok?
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Reply #10 - Oct 24th, 2010 at 9:38pm  
Thanks to Oasis Networks for coming with advice..

The NOC should know what type BUC you are supposed to have:

Cable frequency + BUC LO frequency = satellite frequency

Standard Ku band BUC:   950 to 1450 +13050 = 14000 to 14500 MHz
Extended Ku band BUC:   950 to 1450 +12800 = 13750 to 14250 MHz

The two types of Ku band BUC have different up-converter local oscillator frequencies.

NJT5017 is standard Ku band, with LO=13.05 GHz.

You say you have checked the 10 MHz references at the BUCs.  Be very careful, as the DC power may destroy some spectrum analyser input circuits.

Have you checked for DC volts at the BUC when the external power supply is used. Be careful not to short circuit the cable F plug when testing.  The Linkstar has an internal electronic switch to connect the external power socket to the transmit BUC cable.  I would suspect that this cross connection might easily be burned out if the BUC cable is short circuited. The LNB and BUC cables must never be crossed over on Linkstar - it burns out the internal LNB power supply.

Even using the old 3W BUC you will have achieved a 6 dB improvement from the dish size (1.2m > 2.4m) increase.  The 3W to 4W increase only adds 1.25 dB.

Best regards, Eric.
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« Last Edit: Oct 25th, 2010 at 5:42am by Admin1 »  
 
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Reply #11 - Oct 25th, 2010 at 9:38am  
I have +-24VDC at the BUC, and am lucky enough to have a portable spec an with a built in DC block.
I have been unable to get a useable connection to the NOC through the 3W BUC on the 2.4m dish. The NOC tells me that my transmit power is varying significantly.
I am going to take the RCST outside next to the dish to see if it is a cable issue. From there I think I'll attach all the feed components from the old dish to the new one, get it working, and substitute the new components in one at a time.

Best regards
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Reply #12 - Oct 25th, 2010 at 9:55am  
maybe your pointing is good enough for the Rx but not perfect for the Tx?

Your Tx beam on Ku is much smaller than your Rx beam.
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Reply #13 - Oct 25th, 2010 at 10:57am  
How to peak up a dish.

Azimuth: equipped with an azimuth screw, sliding block and two nuts.
Loosen both nuts apart so you can gently swing the dish from side to side, to rest against either nut alternately, either side of the beam peak.
Measure the degraded, off-peak, quality accurately while rested against one nut.
Swing the dish against the other nut and adjust that nut till you get exactly the same degraded signal quality.
Repeat till you are certain that both degraded measurements either side are exactly the same.
Put the dish approx in the middle of the gap between the nuts.
Tighten inwards both nuts by equal amounts, counting turns and flats on the nuts. This will clamp the dish in the exact centre.

Elevation: long drive screw with one nut holding the dish up.  
Use this nut to drive the dish. Move up off the beam peak and measure a degraded level accurately. Mark one flat on the nut with felt tip pen.  Count down turns and flats to exactly the same degraded quality the other side of the beam peak. Half the count of turns and flats (1 turn = 6 flats) and wind the dish to the centre. Try to get an accuracy of 1 flat or 1/6th of turn.

It will normally take at least 30min to peak up the dish. Think in terms of the receive beam being very rounded on top and your problem is to get to the exact centre of this, so that the narrower transmit beam is centered. You can't peak up just by maximising the measured quality of the receive beam. Once near the beam peak, if you alter the position by 1 or 2 flats you will be unable to determine if the receive signal has got better or worse due to measurement uncertainty.  It is far easier to make the measurements well off the beam peak where the slope of the beam pattern is steep and 1 flat makes a distinct measurement change.

Best regards, Eric.
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Reply #14 - Oct 25th, 2010 at 11:47am  
Dear Tim,
My name is Jawwad and am managing Linkstar/Viasat hub. I have 130 remote sites.
1- check #1: R u on correct satellite?
2- Check #2: If yes, then wt is the status of ur SAT light?
3- Check #3: If SAT is blinking and u are locking ur hub outbound carrier then check ur Transmit cable and its connectors.
4- Check #4: if cable is ok, then check the BUC freq that you are transmitting and wt are the satelllite Trans freq?
5- Check #5: If both freq are matched then check the BUC through ur spectrum analyzer.
6- Check #6: if you do not have the spectrum analyzer then install this BUC to 1.2 m antenna and see the trans. If u can lock ur hub then check the feed of 2.4m antenna.
7- OMT is Passive device so Please ensure the if ur satellite is cross pol then ur feed should be cross pol and if ur sat is co-pol then ur feed should be co-pol.
8- If you are using TX reject noise filter then remove it and put ur BUC directly to the feed and then find the prob.

Thankx
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Reply #15 - Oct 25th, 2010 at 12:27pm  
Dear Tim,

Following Hussain post,

Another basic thing worth checking (the devil in the small details..)

Did you make sure your BUC is connected on the right arm of the OMT? The LNB should be connected to the arm with the RTF and the BUC should be connected to the waveguide arm without a filter.

Did you make sure you are on the right polarity settings? (cross/co pol)?

Did you make sure the BUC is aligned correctly with the waveguide of the OMT and not penpendicular to it?
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Reply #16 - Nov 3rd, 2010 at 3:10pm  
Hello

I have now got our new system (2.4m dish, 4W BUC) working.

Being able to work on the dish intermittently between other jobs made it difficult to fault find in a logical manner. I tried running a new cable to the old dish, mainly to see if my cable terminating skills were the problem. In doing so I improved the Rx signal strength by 1dB.
I decided to try rerouting the cable to my new dish to shorten the length. After creating a new cable entry point and running a new shorter cable (from 25m down to 15m), the modem achieved Tx sync. I now have an improved BER, Rx signal strength and connection speed over the old system (1.2m dish, 3W BUC).
I would not have thought that a 25m cable would be too long, but it seems as though it was.

I am very thankful to all who contributed suggestions.

Tim
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