Skew question and flipping a dish 180

[scottc98]

All,

Need a couple of quick questions answered.

1) When adjusting lnb skew, while facing the dish, is it clockwise for - and counterclockwise for + ?

2) If I flip the dish upside down, will that require me to change the skew?

Got a 90cm on a loan and trying to see if I can get T12. With a 7.9 elevation, it makes it a little difficult right side up

 

[Mr Tony]

All,

Need a couple of quick questions answered.

1) When adjusting lnb skew, while facing the dish, is it clockwise for - and counterclockwise for + ?

I can't remember whats + versus - but anything to the west of true south is counterclockwise skew

2) If I flip the dish upside down, will that require me to change the skew?

no since the dish is flipped 180 degrees the skew is also 180 degrees flipped which is fine...now if it flipped 90 degrees then the skew would be backwards

 

[scottc98]

Thanks Ice!

Confirmed that the + and - is correct. Just wanted to make sure that the 180 flip wouldn't require me to change the lnb skew (its -47 for this sat )

As far as adjusting elevation when its upside down, it would be the same setting as right side up? it just allows you to go lower in elev cause the LNB arm itsn't hitting the pole .

Correct?

 

[tvropro]

I can't remember whats + versus - but anything to the west of true south is counterclockwise skew



no since the dish is flipped 180 degrees the skew is also 180 degrees flipped which is fine...now if it flipped 90 degrees then the skew would be backwards

: Hey Ice, What would happen if you took an eliptical (wider than taller) and flip it so it's taller then wider? I know when there taller than wider there suppose to work better as far as adjacent satellites interference goes. May work better with G-10 and G-25

 

[bill190]

...As far as adjusting elevation when its upside down, it would be the same setting as right side up?...

If it was a "prime focus" dish with the LNB in the center like big dishes, then the angle the dish is tilted and pointing toward the sky would be the same if upside down.

However with an "offset dish" where the LNB is mounted below the dish on an arm, then the angle the dish is tilting toward the sky would be different if the dish was upside down.

Here are is an explanation and drawing of how the different dishes actually "aim"...

http://en.wikipedia.org/wiki/Offset_antenna

 

[scottc98]

AHHH! Got to shut it down for the day. this is when I need a birdog

thanks everyone

 

[Mr Tony]

: Hey Ice, What would happen if you took an eliptical (wider than taller) and flip it so it's taller then wider? I know when there taller than wider there suppose to work better as far as adjacent satellites interference goes. May work better with G-10 and G-25

just skew it properly and it wil work. If the LNB cannot be skewed and you skew the whole dish, then the V polarity will show up as H and vise versa

the frequencies will be the same

 

[Anole]

What would happen if you took an eliptical (wider than taller) and flip it so it's taller then wider?
I know when there taller than wider there suppose to work better as far as adjacent satellites interference goes.
May work better with G-10 and G-25

I see those dishes on gas stations. They're equipped with transmitters.

I believe those dishes are wider to confine their beamwidth to not interfere with adjacent satellites.
So, it stands to reason, that they receive the same way - with a narrow focus on a vertical line where the satellites are in space.
Turning one 90º would therefore be counter productive.

But if you did, for gosh sakes keep the LNB in the same orientation to the dish as it is for regular use!
Rotating the LNB very far off would severely cripple such a dish.
I think those skew the entire dish assembly to avoid skewing the LNB.

 

[tvropro]

I see those dishes on gas stations. They're equipped with transmitters.

I believe those dishes are wider to confine their beamwidth to not interfere with adjacent satellites.
So, it stands to reason, that they receive the same way - with a narrow focus on a vertical line where the satellites are in space.
Turning one 90º would therefore be counter productive.

But if you did, for gosh sakes keep the LNB in the same orientation to the dish as it is for regular use!
Rotating the LNB very far off would severely cripple such a dish.
I think those skew the entire dish assembly to avoid skewing the LNB.

An engineer told me a while back that if the dish is taller then wide it works better at 2 degree spacing. What your saying is the opposite I believe. Let's look at some things here. If a dish has more width it should see more sky east to west, which would be better to see more than one satellite (2 lnb's), but have more of a chance to get interference also. The opposite hold's true if the dish is narrower and taller. It would see a smaller chunk of the sky east to west but the extra height would increase the gain in that smaller area.

That's why I wondered if you turn an eliptical (wider but shorter) 90 deg you would think it would work better at 2 degree spacing

 

[ftarock]

I don't see how one can mount the prime focuse dish upside down...., regardless what one does, it always looks the same...

If it was a "prime focus" dish with the LNB in the center like big dishes, then the angle the dish is tilted and pointing toward the sky would be the same if upside down.

However with an "offset dish" where the LNB is mounted below the dish on an arm, then the angle the dish is tilting toward the sky would be different if the dish was upside down.

Here are is an explanation and drawing of how the different dishes actually "aim"...

Offset dish antenna - Wikipedia, the free encyclopedia

 

[ftarock]

It's the opposite to your thought. If the dish has more width, it sees more of the main sat, not more of the sky. Remeber the dish is eliptical, not a flat board.
For the dish has more width, it has narrow beamwidth.
In summary, the narrower the main beamwidth is, the less signal of the nearby sats come to the dish (also called as sidelobe)
For that reason, I bet you don't see any gas station install your dish the way the engineer suggested...

An engineer told me a while back that if the dish is taller then wide it works better at 2 degree spacing. What your saying is the opposite I believe. Let's look at some things here. If a dish has more width it should see more sky east to west, which would be better to see more than one satellite (2 lnb's), but have more of a chance to get interference also. The opposite hold's true if the dish is narrower and taller. It would see a smaller chunk of the sky east to west but the extra height would increase the gain in that smaller area.

That's why I wondered if you turn an eliptical (wider but shorter) 90 deg you would think it would work better at 2 degree spacing

 

[tvropro]

It's the opposite to your thought. If the dish has more width, it sees more of the main sat, not more of the sky. Remeber the dish is eliptical, not a flat board.
For the dish has more width, it has narrow beamwidth.
In summary, the narrower the main beamwidth is, the less signal of the nearby sats come to the dish (also called as sidelobe)
For that reason, I bet you don't see any gas station install your dish the way the engineer suggested...

Ok that makes sense because of the elipse. I guess the engineer guy wasn't as smart as he thought