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Margin of error?

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IMVexus
Ex Member


Jul 3rd, 2010 at 8:10pm  
Hi all,

I recently purchased service from WAFA and assembled the dish.  I followed directions on this forum to get all the right angles.  I am in Balad, Iraq and am pointing to the W3A at 7E, however I am unable to get a signal higher than 29.  I noticed a few other people had issues, and unfortunately never said -what- they did to resolve it besides poke around or call BW.

In talking with WAFA they have confirmed all my settings are correct, and I aim at the correct place according to the calculations on this website.  I have eventually scanned all over the entire sky to see if there was something I was missing, hoping to pick up >29 signal, but I never got anything above that, and recently I find it difficult to find that again.

What is the margin of error to receive a signal greater than 29?  If all the modem settings are correct, and the azimuth, elevation and polarisation are correct, how "close" do I need to be to know I'm on the right satellite?

If someone would like to take a look at my config sheet and so on, let me know and I will email them.  I plan to call WAFA tomorrow to see if some time on the phone can sort this out.  Thank you very much.

-Leon
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Eric Johnston
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Reply #1 - Jul 3rd, 2010 at 9:48pm  
The way the signal scale works is as follows:  Initially it acts as a simple noise power meter. You get a reading when the dish is pointed at any satellite.  If you move the dish along the orbit each satellite will give a reading, in range 0 - 29.   This noise power readout has a maximum value of 29.  You have peaked up on a powerful satellite.

Next, if you are pointed at the correct satellite, the correct polarisation, have the correct LNB local oscillator frequency and the config tuning and symbol rate all match up then the demodulator locks and the modem will show a receive LED light and the signal quality scale will immediately jump up to about 90 (in the range 30 - 100).  Now you have your wanted carrier. Peak up.

If your mount is tight and the elevation angle is accurate you are on the correct satellite.  The satellites are in a sloping line (tipped at 42 deg) across the sky, higher up towards due south and lower down towards the west.  Measure your elevation angle.  If it reads say 1.5 deg higher than calculated then you are still likely to be on the correct satellite.  The dish is sagging slightly due to loose polarisation bolts.

To get the polarisation right, you need to be told the correct downlink polarisation name. Then set your antenna to that name. Then apply the adjustment angle.

To get the correct LNB local oscillator (LO) frequency, either use the correct fixed frequency LNB or select the correct LO option for an LNB with options (Tone ON/OFF).

To get correct frequency and symbol rate type in the details sent to you by WAFA.

Best regards, Eric.
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Eric Johnston
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Reply #2 - Jul 3rd, 2010 at 10:00pm  
Regarding receive polarisation (giant circular scale behind the dish).
All below is as viewed with you standing behind the dish and facing forwards towards
the satellite in the sky.


a) If you have the new integrated white Universal LNB/OMT

For Horizontal: Start with the feed arm at the bottom. LNB pointed to the right = Horizontal polarisation.

For Vertical: Rotate the dish 90 deg anticlockwise.  Feed arm is now on the right.  LNB pointing up = Vertical polarisation.

Now adjust the polarisation by calculated amount (e.g. +42 deg clockwise).  Count the
amount of degrees movement if the scale reads backwards and ignore the numbers.

b) If you have old grey OMT/filter assembly with the LNB as separate module.

For Horizontal: Start with the feed arm at the bottom. LNB arm pointed upwards = Horizontal polarisation.

For Vertical: Rotate the dish 90 deg anticlockwise.  Feed arm is now on the right.  LNB arm pointing to the left = Vertical polarisation.

Now adjust the polarisation by calculated amount (e.g. +42 deg clockwise).  Count the
amount of degrees movement if the scale reads backwards and ignore the numbers.

Best regards, Eric.
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IMVexus
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Reply #3 - Jul 4th, 2010 at 12:35pm  
Hi Eric thanks for the help.

Your directions are good, and lead me to thinking that indeed I am aiming correctly.

By margin of error, I mean, how close in degrees do I need to be to pick up a 30+?  If all the settings are correct, and I'm aiming at W3A, which is a few degrees off the satellite at 10E, how do I tell if I am close?  From my understanding, when I point near W3A, the signal should go over 30 - but if I am a couple degrees off, will I get some indication?  Does it stay 29 until I am right on it?  I was under the impression that the wide satellite beam would give me some sort of reading even if I were close, which I believe I am.

Thanks for the help.

P.S. I was given a frequency of 9992 and 7000000sps on my RPR form for the W3A satellite.  If there is any way to confirm if these are correct, I'd like to know.  Thanks.
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Eric Johnston
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Reply #4 - Jul 4th, 2010 at 5:29pm  
Yes, it should go over 30 when you are pointed at W3A.

But it doesn't.  The reason is that you have wrong polarisation, wrong polarisation adjustment angle, wrong LNB, wrong tuning or wrong symbol rate.

As it is, as you approach the satellite the low value display reading will increase to 30, stay at 30 for while and then decrease as you move away from the satellite. If you go up and left, to the east, you will find another satellite, that may also go up to 30.  The next satellite on the other side, to the west, is down and to the right.  A weak satellite will not go up as far as 30.
I don't know how wide is the 30 at the top of your beam so I can't answer your question about margin of error.  If you want to get to the exact centre of the 30, adjust either side down to exactly 25 and then mechanically halve the distance between the two 25s.

If your measured elevation is the same as calculated elevation then it is likely that you are pointed at the correct satellite and it is time to work on the polarisation and configuration.  The adjacent satellites, up/left and down/right, will be at least 2 deg away in elevation.

Ask WAFA to verify:
Name of the satellite.
Orbit location of the satellite.
Downlink polarisation name.
* Downlink frequency of the actual satellite carrier.
* Your LNB local oscillator frequency and LNB type/model number, plus 22kHz tone status, if applicable.
* Your modem tuning frequency (tuned units of 100kHz)
Carrier symbol rate.

* WAFA and yourself need to know and cross-check these numbers. Check that modem freq = sat freq - LNB local osc freq.
e.g. Modem (100kHz units) = 12345 = 11.2345 GHz - 10.0 GHz
This example assumes an NJR2184 LNB with 10 GHz LO.
Possible LOs, for a variety of fixed LO LNBs are 10  10.25  10.5  10.75  11.25  11.3 GHz.  
LNBs with switchable LOs often are 9.75/10.6, a few are 10/11.3 GHz. (normally tone, sometimes voltage)
There may be a Hughes LNB called "Pure" 9.75/10.75 GHz. (tone)
Andrew Ku band TRIAs have 9.75 10  10.60 11.3 GHz selectable using external switch module.

Anyone in Iraq operating HX on W3A please tell us your config freq, symbol rate and LNB pull down menu and tone setting, also actual LNB type/model number.

We get a number of people with problems her in this forum, and often, after offering them advice, they go quiet and we hear no more.  When people get systems working please tell us how you did it - what advice worked and what didn't..

Best regards, Eric.
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« Last Edit: Jul 4th, 2010 at 10:53pm by Admin1 »  
 
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IMVexus
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Reply #5 - Jul 15th, 2010 at 10:02am  
Hi Eric,

Thanks for the information.  I'd like to report that I was able to get the satellite working; and here are the details!

After a lot of work attempting to aim the satellite, I gave up, and figured I would call in a local professional installer to get it right.  I know my stuff, so this was a defeat, but ok fork over the cash and get it working.

The next day, I checked my email and WAFA said to change the LNB type to Default instead of Pure.  Ok, sure.  So I do that, and immediately see a 70 signal after the modem resets.  Then after a minute it's down to 23, 14, etc.  I thought ok, maybe it's the aiming not being perfect, but I did see 70, so there was hope.

(Like many others, seeing a 29 might just mean they gave you the wrong settings!  Aiming a satellite is not hard especially with reading this forum!)

So I went to aim the satellite but never got a great signal.  It would be 14, 23, and then sometimes it would hit 30, and every now and then I'd see it jump to 82 or something.  Ok, so I was onto something, but for some reason 90% of the time it was on 14, 23, something low.

Well finally after messing with it for an hour and a half I decided I wasn't going to find any better signal.  I peaked the satellite off the low numbers, ending up with something like 15 and 28, with 30 popping up more than a couple times in a row.  So I -knew- I was on the right satellite.  I went down and on a whim, decided to turn off the modem and turn it back on.  As soon as it turned back on, I noticed the receive LED kick on and stay on, which normally it would kick on for 2 seconds before going off when I was aiming it.  Ok, so I bring up the status page and viola, I have a 91 signal holding strong.

Needless to say I was pretty pissed having to spend all that time making changes to something that didn't need changing in the first place.  I realize now that when I activated the OPI from the modem, the signal would always drop out, so there was no chance of me being in the right spot.  That, along with the different LNB type probably gave me no chance - I had reset the modem many times while pointed correctly with the incorrect settings.  My advice to anyone in the future doing this is to aim the satellite according to the values given to you by the azimuth, elevation, and polarization calculator, double check you have the right settings, then turn on/reset the modem.  Trust your aim, also.

I've had it running for a little bit here.  I've run into a new issue where the past day I haven't been able to access most websites unless I try 10+ times to connect to that website.  Not sure what's going on but I'm trying to get information from WAFA about it.  So there's more administrator-ing to be done!

Thanks for the help Eric!

Sincerely,
Leon
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