LNB skew vs DISH skew

[jenom]

I have a small dish (around 22") which rotates.
Thinking of removing rotating parts and attach it to a larger (30") dish to make dish skewable.
I would like to know whether it is worth the effort, and I will end up with some gains compared to just skew the LNB on a same dish?
Thanks for all replies!

 

[Anole]

Round dishes you usually skew the LNBF.
Elliptical (oval) dishes, you usually skew the entire dish.

(there are exceptions, and they all have good reasons)

I'd call a 30" dish just minimal size for general Ku FTAing.
If it's round and you're going to set it up fixed-aimed, just skew the LNBF.
If you put it on a motor, the point is moot, 'cause the motor skews the entire assembly. - :up

What sort of dish are you going to use?

 

[jenom]

The dish I called round is a 21" wide, and 22" tall, has a Y shaped dual LNB holder and it has a canadian satellite provider logo printed on it.
I am thinking to take of the rotating mechanism and use it on a 30" qsat dish, which is already in use for fta, works fine for 30,72,89,97,101
My question is: do I gain anything (other than experience) by making the dish skewable ? (instead of skewing the LNB)
Thanks!

 

[phlatwound]

Sounds like your dish is a typical "round" offset dish. That shape is a section of a parabola, and your LNBF "sees" it as being truly round.

That being the case I will quote what Anole said previously (since he nailed it perfectly):

"If it's round and you're going to set it up fixed-aimed, just skew the LNBF.
If you put it on a motor, the point is moot, 'cause the motor skews the entire assembly. -

"

In a typical circumstance, no appreciable gain to be had by making your dish skewable.

 

[Mr Tony]

wont work. The focal length on a Bell/Dish dish is different than a 30" dish (actually each size dish has a different focal length)

 

[jenom]

From the replies, I think I did not described the situation clearly:
I am planning to take of the rotating mechanism from an unused Bell dish
It has 2 parts: Part 1 is attached to the back of the dish with 4 bolts, Part2 is which goes to the pole.....and these two part a held together with 2 bolts only.
On the 30" dish, I will install a small rectangular metal plate adapter at the back, using the original 4 holes already on the dish. (I do not want to make new holes)
Then drill 2 holes the adapter plate to attach the original 30" dish's lnb arm to this adapter plate . (so the focal lenght will same as before)
Next drill 4 holes an the adapter plate and mount the Bell rotating mechanism to this adapter plate
Of course, I will need to cut of the lnb arm from the Bell part # 1 .

My theorical question is: Would I get any gain (dB) if I make a dish skewable , instead of skewing the LNB only ?

(PS: I wish I can make some pictures, but my digital camera just stopped working recently) )

 

[Mr Tony]

ok now it makes sense

you probably wont notice much difference on a stronger transponder but you might notice a few point gain on weaker feeds especially at the end of your arcs (the further away from true south)

 

[jenom]

sounds like it would not worth the effort [ lots of work, dish would get heavier (extra plate)]
Thanks for all the replies!