Prime Focus or Offset Dish ?

[Greg Mueller]

Is either more efficient?
If they are the same size, does an offset dish have more gain?

Seems like the prime focus type would be more efficient.

Second question...
How small must the holes be on a prime focus mesh type dish, to work for KU?

With all the small (6'-8') C-band dishes laying around unused it would seem like the perfect FTA dish, unless the offset design is somehow better.

 

[lilyarbie]

From what I've heard....

Offset is better than Prime Focus due to the fact that the feedhorn assembly is not placed exactly over the focal point of the dish and thus blocking the focal point of the dish. I haven't seen any offset dishes bigger than 6 foot dish. They probably do make them, but I would imagine they would be rather more expensive than prime focus. The 6 foot prime I saw in a magazine was much more cheaper than it's offset counterpart.

 

[Mr Tony]

Prime focus dihes usually are buildable whereas offset arent

My 6 foot PF dish is in 6 pieces (the dish itself)

 

[mbarnes]

Offset is better than Prime Focus due to the fact that the feedhorn assembly is not placed exactly over the focal point of the dish and thus blocking the focal point of the dish. I haven't seen any offset dishes bigger than 6 foot dish. They probably do make them, but I would imagine they would be rather more expensive than prime focus. The 6 foot prime I saw in a magazine was much more cheaper than it's offset counterpart.

I've got an offset feed 2.4m (8ft) dish on my uplink and two of my downlink locations have 2.4m offset dishes. Offset feed dishes are a lot more expensive in the larger sizes. I just got a quote for $2500 for an Andrew 2.4m offset RX only dish, compared to just under $1000 for prime focus.

For you northern guys, the snow slides off the offset feed dishes much better