Correct LNB Skew Value

[SMRGroup]

Folks,

I've got eight LNBs on my dish, which itself has a 4° skew to match the arc of the various satellites (at the moment I'm receiving Astra 1/2 at 19.2°E around to Atlantic Bird 2/Telecom 2D at 8.0°W). The skew for each was set using a stand-alone meter and the quality fine-tuned using the meter in a spare receiver, I basically turned each LNB to achieve the best signal quality.

Measured using a small inclinometer, Astra 1/2 has a skew of about -12° and Atlantic Bird 2 about +35°. I decided to fine-tune using the values given by the Satlex calculator only to find most of them are miles off...

The closest is Astra 1/2, for my location Satlex says it should be -15.74°, but the futher west I go the more error there is - for Atlantic Bird 2 Satlex reckons the skew should be +3.81°, which is about 31° difference!

If I move the LNB to the given values, the signal strength and quality both fall off considerably (quality drops from ~80% to 25% on Atlantic Bird 2 which means I would probably lose the signal on a rainy day).

So I'm wondering what gives? Perhaps I'm interpreting the Satlex figures incorrectly? Any pointers would be appreciated.

 

[rolfw]

The problem is possibly that your skew on the dish cannot be correct for both sides of the arc from your due South. I use the swedish Microwave calculator for rough guides, but at the end of the day, set the LNBs at whatever angle works best.

 

[IjonT]

for Atlantic Bird 2 Satlex reckons the skew should be +3.81°, which is about 31° difference!

I've found following information on one website:
On some satellites the polarity angle can be offset from the calculated one.

On the France Telecom Satellites there is a polarisation offset of 20 degrees from the calculated ones.

 

[SMRGroup]

The problem is possibly that your skew on the dish cannot be correct for both sides of the arc from your due South. I use the swedish Microwave calculator for rough guides, but at the end of the day, set the LNBs at whatever angle works best.

Thanks for the helpful reply! The skew on the dish is 4° so I only expected an error of ±4°. The odd thing is that Sirius 2 at 4.8°E is essentially in the centre of the dish, so its skew doesn't apply and the LNB is essentially at 0°, even though the Satlex calculator has it at -5.73°. It seems the further east I go, the larger the skew discrepancy becomes.

One quick question; should the skew on an LNB always be measured against the vertical/horizontal, or should any dish skew be taken into account?

 

[SMRGroup]

On the France Telecom Satellites there is a polarisation offset of 20 degrees from the calculated ones.

Thanks IjonT, I guess something like that could be happening here.

 

[PCD]

Folks,

I've got eight LNBs on my dish, !

.

As a matter of interest, why ? Surely a motor will cost no more. Is it because a number of people watching different sats at the same time ? Regards.

 

[Likvid]

Skew should be measured from the H/V plane.

Thanks for the helpful reply! The skew on the dish is 4° so I only expected an error of ±4°. The odd thing is that Sirius 2 at 4.8°E is essentially in the centre of the dish, so its skew doesn't apply and the LNB is essentially at 0°, even though the Satlex calculator has it at -5.73°. It seems the further east I go, the larger the skew discrepancy becomes.

One quick question; should the skew on an LNB always be measured against the vertical/horizontal, or should any dish skew be taken into account?

 

[SMRGroup]

As a matter of interest, why ? Surely a motor will cost no more. Is it because a number of people watching different sats at the same time ? Regards.

The dish is designed for a 40° arc, just-in-case you were thinking I'd got lots of LNBs crammed together... ;)

Lots of reasons - the total price was probably a bit more than a motorised dish, but here are some of them:

1) No motor noise
2) The dish is in a really windy spot and it kept knocking the motorised system out of alignment
3) I can't get anything more westerly than Astra 1/2 so the 40° arc covers everything I could get with a 1-1.5m motorised dish

...and the cool stuff...

4) I can watch more than one satellite at the same time (PIP or side-by-side)
5) I can record more than one satellite at the same time (two tuners)
6) Channel surfing is instant, no waiting for the dish to move

The last point takes a bit of getting used to if you've come from a motorised system, I can just sort the entire channel list alphabetically and surf through it, if consequtive channels come from Astra 1 or Atlantic Bird 3, the user really doesn't know it, the switch is instant and seemless.

If I wanted to feed a second system, it could also recieve multiple satellites (using dual-feed LNBs) and both would be completely independent, unlike with a motorised system.

So far, as the commercial says, I'm loving it.

 

[PCD]

Thanks. Interesting !

 

[Schnuffi]

Folks,

I've got eight LNBs on my dish, which itself has a 4° skew to match the arc of the various satellites (at the moment I'm receiving Astra 1/2 at 19.2°E around to Atlantic Bird 2/Telecom 2D at 8.0°W). The skew for each was set using a stand-alone meter and the quality fine-tuned using the meter in a spare receiver, I basically turned each LNB to achieve the best signal quality.

Measured using a small inclinometer, Astra 1/2 has a skew of about -12° and Atlantic Bird 2 about +35°. I decided to fine-tune using the values given by the Satlex calculator only to find most of them are miles off...

The closest is Astra 1/2, for my location Satlex says it should be -15.74°, but the futher west I go the more error there is - for Atlantic Bird 2 Satlex reckons the skew should be +3.81°, which is about 31° difference!

If I move the LNB to the given values, the signal strength and quality both fall off considerably (quality drops from ~80% to 25% on Atlantic Bird 2 which means I would probably lose the signal on a rainy day).

So I'm wondering what gives? Perhaps I'm interpreting the Satlex figures incorrectly? Any pointers would be appreciated.

You should consider posting a photo of your setup I think many members
would be interested, Was it or is it hard to connect 8 lnbs to a receiver?
Is there much signal lost? I am thinking of doing something similar.
One final question what satellites do you get.

Rgds Schnuffi

 

[SMRGroup]

Was it or is it hard to connect 8 lnbs to a receiver?
Is there much signal lost? I am thinking of doing something similar.
One final question what satellites do you get.

It was much easier than I expected, helped by having a receiver with twin tuners. All I did was position each LNB individually using a meter and the receiver to fine-tune the signal quality, then I used two 4:1 DiSEqC switches, one on each tuner.

When storing satellite information, I specified which of the receiver's LNB inputs to use and then set the correct DiSEqC value to match the LNB. So for example, Hotbird is LNB 1 and DiSEqC 1, while Astra is LNB 2 and DiSEqC 1, Atlantic Bird 3 is LNB 2 and DiSEqC 2... and so on (each switch has values 1-4). It just takes a little bit of planning to decide which satellites to put on each LNB feed for watching or recording two things at once. As Hotbird and Astra are generally the most common satellites in use, separating them make sense.

Right now I am recieving:
Astra 1 at 19.2°E
Eutelsat W2 at 16°E
Hotbird at 13°E
Eutelsat W3A at 7°E
Sirius 2/3 at 4.8 and 5°E (same LN
Thor 2/3 at 0.8°W and Intelsat 10-02 at 1°W (same LN
Atlantic Bird 3 at 5°W
Atlantic Bird 2 and Telecom 2D at 8°W

There's still enough room on the arc of the dish for Eutelsat W6 at 21.6°E and Astra 3A/1D at 23.5°E but I've got a tree in the way and a separate Sky dish anyway. At the other side of the arc, Express 3A at 11°W and Atlantic Bird 1 at 12.5°W are both possibilities, but I'd need a 6:1 12V DiSEqC switch, I believe a 4:1 switch is the most an LNB power supply feed can handle.

I could get Eutelsat W1 at 10°E but there's nothing on it I want to watch, while Amos 1/2 at 4°W and Nilesat 101/102 at 7°W would be a bit weak on rainy days.

Signal quality and strength doesn't seem to suffer at all, going from a cable straight to the LNB and then through the DiSEqC switch, I can't see a noticeable drop-off in either.

When I've cleared up the rats nest of wires I'll try to post a picture.

 

[Schnuffi]

Thank you for your prompt reply sounds interesting I did not
realize that you had a twin tuner that makes it a whole lot
easier. I look forward to see your set up after you clean up the rats nest.

Rgds Schnuffi