Dish focal point calculation

[kuky3]

Hi guys ...
I have a 1.25m prime focus dish with a depth of 22.2cm can someone who understands the calculation do some maths for me regarding the actual focus point ... and is it a constant at both extremes of the ku band ... the highest ku frequencies are giving me problems :frown:

[wolves]

Try a google search for..

satsig net focal length

Some info in first link..

[ozzsurf]

44cm



43.989

[kuky3]

thanks guys .... its at nearly 48cm at the moment ... i'll get to it :)

[ABA]

h**p://www.dmsiusa.com/articles/focal%20distance%20ratio%20formul a.pdf Formulas for calculating focal distance and f/D ratios for C band prime focus
To calculate the focal distance, you have to measure the diameter (D) and the depth (d) of the
dish. Measurements should be in the same units of measure (you can't use feet for the diameter
and inches for depth). For the example, we will say we have a dish that is 120 inches in diameter
(D) and 18 inches deep (d).
focal distance (f) equals the diameter squared (D x D) divided by 16 times the depth (16 x d) or :
D x D = 120 x 120 = 14400
16 x d = 16 x 18 = 288
D x D/16 x d = 14400/288 = 50
focal distance f = 50 inches
After you have calculated the focal distance (f), you can use that figure to calculate the f/D ratio
of your dish. In this case, using the same diameter (D) = 120; and the calculated focal distance
(f) = 50
f / D = 50 / 120 = .416
f /D = .416 which you would round up to give you a setting of .42
The list below shows how far the throat is out from the scalar rings for different f/D settings.
EXAMPLE: A dish with a .42 f/D will have the throat about flush with the rings.

[BM300]

Thanks for the useful information.
Here is another site for dish focal and F/D ratio calculation:
h**p://www.satlex.de/en/fdratio-params.html?diam=180&depth=30