Need some one to check my work

[Long Hair]

I have a unimesh dish 7.5ft, I'm trying to find out my F/d ratio. Here is what I have
7.5 x 12 = 90inches diameter of the dish, 13.5inches depth in inches 90x90=8100, 16x13.5=216. 8100/216=37.5inches 37.5/90=0.416666. If this is right how do I set the F/D to 37.5 when I'm maxed out at 36inches. Any info would help. The reason I'm asking is because some tp's don't come in on my 4dtv box. example on g1 @ 133west I get stars mux but not HBO.

 

[phlatwound]

Sounds like you are confusing focal length with F/d ratio.

F/d ratio is the measurement of the depth of your feedhorn in the scalar ring. Depending on what type/brand of feed you have you may see some numbers and lines on the tube that sticks into the scalar ring? That is where you set your F/d ratio.

The focal length is the distance from the flat of the center of your dish to (I think) about 1/4" into the mouth of your feedhorn.

 

[Lynskyn]

If I recall correctly the Unimesh 7.5 has an f/d ratio of .40 so that would be the scalar ring setting and the focal distance is 36" to about 1/4" into the feedhorn throat.

 

[Long Hair]

If I recall correctly the Unimesh 7.5 has an f/d ratio of .40 so that would be the scalar ring setting and the focal distance is 36" to about 1/4" into the feedhorn throat.

Well that's about what I'm set at my focal distance is 36in if I go 1/4in in on my feed. I have a dmx 741 lnbf would I set the f/d to 2 on that. Going off this chart at the bottom of the page.Tune Up Of Your Satellite
thanks
http://www.bigdish.info/mainten/focal.html

 

[Lynskyn]

If there is no .40 tick mark like on the Chaparral feed then yes, measure .20" (1/5") up from the feed throat to the bottom of the scalar ring.