Advice Needed Before I make a complete ass of myself again!

[Archive4]

Following on from the tests I have run in this thread New Lnb changer , and having read the links from it regarding " centre point " or as previously named in another thread " le G spot ", I have one simple question.

Should an offset dish lnb aim directly at the centre point of the dish, in the same way a prime focus dish does?

To explain it better, if a dish is 80 wide and 100 high, should the lnb be aimed at 40 from the left and 50 from the bottom? ( or 40 from the right and 50 from the top, whichever bursts your bubble )

I was thinking about asking the design people at Laminas why my laser spot is 40 mm below where I think it should be. But, as the title states..........

 

[Captain Jack]

There's a formula to calculate where the LNB should point. It depends on the dimensions, the offset angle and the depth of the dish. Rimant will be along shortly....

 

[RimaNTSS]

Should an offset dish lnb aim directly at the centre point of the dish, in the same way a prime focus dish does?

NO!
@Captain Jack , when you mention me, you better put @ before my nickname, otherwise I can miss interesting questions

 

[Archive4]

There's a formula to calculate where the LNB should point. It depends on the dimensions, the offset angle and the depth of the dish. Rimant will be along shortly....

I wanted a simple, layman´s answer, centre of dish or not?
I don´t want to download a piece of software that will tell me I need to see a shrink, I already know that much

 

[RimaNTSS]

I wanted a simple, layman´s answer, centre of dish or not?

NO!

 

[John]

Following on from the tests I have run in this thread New Lnb changer , and having read the links from it regarding " centre point " or as previously named in another thread " le G spot ", I have one simple question.

Should an offset dish lnb aim directly at the centre point of the dish, in the same way a prime focus dish does?

To explain it better, if a dish is 80 wide and 100 high, should the lnb be aimed at 40 from the left and 50 from the bottom? ( or 40 from the right and 50 from the top, whichever bursts your bubble )

I was thinking about asking the design people at Laminas why my laser spot is 40 mm below where I think it should be. But, as the title states..........

My CM offset was the same, ie: approx 40mm down from centre. My 1.2 CM offset also has a G spot lower than centre .... over to you Rimants

 

[Archive4]

NO!

OK, so on a bulk standard offset dish, should the laser hit above or below horizontal centre?

 

[RimaNTSS]

For CM 1,2m G-spot is about 115mm down from center. For another dishes can be different, but bottom line is that for offset dish G-spot is always lower than center. That is the beauty of the offset dish.

 

[Archive4]

For CM 1,2m G-spot is about 115mm down from center. For another dishes can be different, but bottom line is that for offset dish G-spot is always lower than center. That is the beauty of the offset dish.

Why make the dish so big then, if g spot is 115mm below on a 1.2 m dish, may as well be a 90 cm dish?

 

[Captain Jack]

From space, an offset dish looks round. So a 1.8m dish that is 1.8m horizontally and 2.0m vertically appears as a round 1.8m dish. This is because unlike a prime focus dish, that looks directly at a satellite, an offset dish looks at the satellite at an angle (the offset angle). It's that angle that causes the vertical dimension to look smaller than it is.

I think........

 

[RimaNTSS]

I think........

You think perfectly right CJ. On attached picture green line shows direction from satellite to the dish and it hits to the G-spot, which is not the center of the offset dish.

 

[Archive4]

OK , on my Laminas 1.8 m dish the G spot is about 40 mm below centre, so why is it 115 mm below on the CM 1.2 m dish?

 

[RimaNTSS]

on my Laminas 1.8 m dish the G spot is about 40 mm below centre

On your Laminas 1,8m LNB is pointing 40mm below the center, but that does not mean that real G-spot is 40mm below the center (most likely it is even lower).

 

[Archive4]

On your Laminas 1,8m LNB is pointing 40mm below the center, but that does not mean that real G-spot is 40mm below the center (most likely it is even lower).

OK , I sit corrected, what I was trying to say is the laser points 40mm below center when correctly sitting in the lnb holder made by the manufacturer

 

[RimaNTSS]

the laser points 40mm below center when correctly sitting in the lnb holder made by the manufacturer

Yes, and this does not mean that manufacturer made it perfect. Do you confirm that working area of Laminas 1,8m is 1800 x 1935mm? If so, than G-spot should be located about 800mm from the point "B" (bottom point of the working area of the dish).

 

[Archive4]

When you say point B from the bottom of the dish, is this point B as measured round the dish face, or point B measured in a vertical line from top to bottom of dish, like this ( which I borrowed from lnb changer thread )

 

[RimaNTSS]

When you say point B from the bottom of the dish, is this point B as measured round the dish face, or point B measured in a vertical line from top to bottom of dish, like this ( which I borrowed from lnb changer thread )

No, my pint "B" is quiet different from Wim's point "B". On the attached picture I circled my point "B" in "Navy blue" color. So, point "B" is the lowest point of the working area of the offset dish.

 

[Archive4]

OK I get that, but is it from point B directly vertical 800 mm or via dish face which would be approx 900 mm?

 

[RimaNTSS]

No, from point "B" directly to the point "G" = 800mm (red line on the attached picture).

 

[Archive4]

OK if I get this right, from point B to point G in a direct line should be approx 840 mm on a straight line across dish face and approx 937 mm allowing for dish indentation on a standard offset 1.8 dish?