Dish Alignment and Polarization Contradiction

Hello,

Located near Kandahar, Afghanistan.

I currently have 1 HX50 VSAT set up (I fell in on it when I arrived here, so it was already set up and functioning).

I am attempting to set up a second system to link them together via the BW-offered Draytek router. It is called the "Dual 2000" system.

I set up the second dish yesterday but not-surprisingly ran into problems once I started the dish-pointing procedure.

(Question: Does it matter how close or far apart the 2 dishes are from each other? I currently have the new dish situated approximately 15 meters in front of and 1 meter left of the old/current dish. They are both pointed slightly to the right and so both have a clear line of sight to the horizon. I presume there is no issues with that -- please confirm.)

When I used the BW dish-alignment page, I entered in the exact coordinates of the dish and it gave me the following information:
[quote]
Satellite: W3a: 7°

Dish elevation (deg): 17.9°
Dish azimuth (deg east relative to true north): 252.46°
Dish azimuth (deg east relative to magnetic north): 250.23°
Polarisation angle (deg): -54.38°
Counter clockwise rotation whilst standing in front of the feed assembly, facing the dish.
[/quote]

(Question: Is the w3a satellite a "Eutelstat" satellite? I've seen mentioned in a few places that I have to add 3.5 degrees to the polarization?)

Most of my confusion comes from the technical manuals which arrived in the boxes, and how it seems to contradict what the BW Youtube video shows.
I believe I am supposed to have a vertical receive polarization, because the current functioning HX50 states vertical receive in the modem's advanced settings page. Therefore I rotated the assembly so the LNB is vertical, and affixed the cone so that the single mark is up and lined up with the LNB, and the fat lump is down towards the feed support tube. Now, am I supposed to rotate the entire dish (using the scale on the back of the dish) to -54.38 degrees? Or do I leave the dish at 0 and rotate the feed horn assembly to -54.38 degrees? The manual states that the feed horn assembly should only rotate +/- 7 degrees within the bracket, but in the BW youtube video the bracket is not present and the guy is rotating the horn assembly way more than 7 degrees! Argh!

BW has supplied me with a MaxPeak SAM-lite2 meter. Here is what I find odd: the current functioning dish has a signal strength of 91 and a rate code which fluctuates between 1/2 and 2/3. I have been using it for the past 4 months with no issues, and can see download rates of up to 130 KiB/s. When I disconnect the cables from that system, and plug the meter into the LNB, it never finds the w3a satellite!! The meter has the most up to date meter-file from December 23, 2011, and I've tried multiple cables to connect it to the LNB. What could be the reason for the meter not finding the satellite, but the modem finds it immediately? The meter only ever gets up to about 70 dBuV, and never actually finds w3a. How could this be?

Thanks for any assistance you can provide. I can take pictures of the setup if you think it will help.

Assuming adequate frequency diversity, dish spacing is not critical. 15 feet with 2w transmitters is safe. But you must select operating frequencies carefully to avoid mutual interference. W3A is indeed a Eutelsat, but Eic has the inclination error listed at a negligible 0.1 degree. The list is here: https://www.satsig.net/sslist.htm

What jumps out at me, is no mention of satellite parameters for the second dish. Are you sure both dishes are even assigned to the same satellite? The operational system you inherited will list the current satellite parameters for that specific account. They will not be shared by the 2nd dish, that will pretty much guarantee mutual interference. So let's back up and take a look at the satellite parameters for the 2nd dish, and go from there.

Oh, and a Rate Code that vacillates between 1/2 and 2/3 suggests a pointing error. Given a Signal Strength of 91, it's almost certainly the POL angle. You should be able to fine tune that all the way up to 4/5. But let's limit this to one problem at a time for now.

//greg//

Greg -- interesting point about using the same satellite. I had not thought of that. That wouldn't explain the fact that my satellite meter cannot detect w3a, though, right? Or the fact that the meter cannot find w3a when I hook it up to the LNB on the currently-working dish??

I will have to ask BW if I'm supposed to be aiming at a different dish.

Eric -- is there something else I need to do to configure the SAM-lite2? I'll look at the downloads page on the MaxPeak website.

Please confirm that the method I used to set the polarization is correct: cone assembly has the LNB sideways (pointed left when facing the satellite), with the single-tick and 505 pointed UP away from the support tube. I then rotated 90 degrees clockwise (when facing the satellite), and then counted backwards FROM 90 degrees the 54.38 degrees.

Should I just drop the meter and go straight to using the HX50 to align?

Thanks.

OK. Apparently my sat meter needs a frequency list update, so perhaps I'll toy around with the HX50's pointing utilities and see if I get anything.

It turns out I'm supposed to be aiming for W6, not w3a!
BW also says I should have both dishes aimed at W6, and not two seperate satellites. I would guess that Greg is right if it was 2 dishes operating under the same modem, but since I have 2 seperate HX50s, they should uniquely identify themselves to the satellite I would think.

I suspect that though my first dish does work, it's not ideally calibrated on its polarization either. The dish itself is at 0 degrees rotation and the feed assembly is what's rotated. Despite BW recommending to me to leave the dish at 0, I'm inclined to listen to you guys and the manuals which came with the dish, as it makes more sense to rotate the dish (since it is assymetric)!

-Austin

The W3A satellite is being maintained in its orbit stationkeeping box of approx +/- 0.1 deg, so that fixed pointing small earth station antennas may be used.  Its inclination is always increasing at approx 0.8 deg per year due to sun and moon, and to keep it below 0.1 deg, station keeping operations are done frequently.  Inclination is a positive number, but you can think of it, at times, as negative, for example if you launch the satellite into an initial orbit with a 'negative' inclination of say 0.4 deg such that after 6 months its orbit inclination reduces to zero, having used no fuel for 6 months. You then start stationkeeping for 15 years, then allow it to go into inclined orbit mode, with only E-W stationkeeping for say a further 5 years, by which time the inclination has increased to about 4 deg, which needs tracking ground antennas.

The polarisation of virtually all satellites is either parallel with the equator or the earth's axis.  A few satellites have their polarisation tilted.  Some Eutelsat satellites may have +3.5 clockwise and Astra may have 7 deg clockwise. Quite which satellite have the anomaly is not known. It was done early on to reduce cross-pol interference due to the flat underside of raindrops that would be less of a problem if the polarisation was parallel to or at right angles to the ground in the middle of the coverage area.

When you set up linear polarisation be prepared to make a final adjustment of a few deg either way according to what the teleport hub tell you to do. They can see your CW carrier in the cross pol transponder and help you verbally into the exact deep null, so that you do not cause interference to others or suffer interference from others, now or in the future.

Best regards, Eric.