Thread: primefocus

Would this 3ft primefocus have any advantages/disadvantages over an offset of the same size? Could you use a HH motor with it, or would that mess up the skew?
http://www.daveswebshop.com/panku.shtml

A primefocus gathers more snow and it takes longer to fall off.

Originally Posted by CbandLover

Would this 3ft primefocus have any advantages/disadvantages over an offset of the same size? Could you use a HH motor with it, or would that mess up the skew?
http://www.daveswebshop.com/panku.shtml

"There are 2 main design disadvantages on Prime focus antennas....... the feedhorn and feed support structure block part of the reflector surface and the feedhorn must look back at the dish at such an angle that it can also intercept noise from the "hot" earth located directly behind the reflector. The feedhorn's illumination of the antenna must be attenuated or tapered to minimize noise contribution from the perimeter of the dish. This design necessity acts to reduce the antenna's efficiency.
Prime focus antennas use two different types of feedhorn support bracket. A three or four-legged support provides a rigid support structure for the feedhorn and LNB over the center of the dish and at the distance specified by the manufacturer. The main disadvantage of this structural approach is that it may be difficult to make minor variations in the focal length, that is the distance from reflector center to the lip of the feed opening. The buttonhook structural design uses a single support member to position the LNB and feedhorn. This tubular leg can usually be slid in and out of a clamp or bracket at the center of the dish, allowing the installer to fine-tune the focal length. However, the buttonhook support may not always position the feed at the precise center of the dish, especially when the feedhorn is weighted down by multiple LNBs.
Motorized dishes may experience feedhorn movement when the antenna is moved from one satellite to the next...... strong winds can also temporarily move the feedhorn away from the antenna's focus. Guy wire kits are available which the installer can use to provide additional structural rigidity to the "buttonhook" support if required at the installation."

I had a 1.2m aluminium prime focus dish that worked great, I like them!

PSB brings up a good point about the arm on a offset dish. They can move around more. They do make offset dishs that have the main arm and then have two smaller pieces of metal that go to the sides of the dish to help stabilize the LNBF. I believe this is on the higher end dishs. You can add your own if are good with working with metal.

Originally Posted by PSB

"There are 2 main design disadvantages on Prime focus antennas....... the feedhorn and feed support structure block part of the reflector surface and the feedhorn must look back at the dish at such an angle that it can also intercept noise from the "hot" earth located directly behind the reflector. The feedhorn's illumination of the antenna must be attenuated or tapered to minimize noise contribution from the perimeter of the dish. This design necessity acts to reduce the antenna's efficiency.
Prime focus antennas use two different types of feedhorn support bracket. A three or four-legged support provides a rigid support structure for the feedhorn and LNB over the center of the dish and at the distance specified by the manufacturer. The main disadvantage of this structural approach is that it may be difficult to make minor variations in the focal length, that is the distance from reflector center to the lip of the feed opening. The buttonhook structural design uses a single support member to position the LNB and feedhorn. This tubular leg can usually be slid in and out of a clamp or bracket at the center of the dish, allowing the installer to fine-tune the focal length. However, the buttonhook support may not always position the feed at the precise center of the dish, especially when the feedhorn is weighted down by multiple LNBs.
Motorized dishes may experience feedhorn movement when the antenna is moved from one satellite to the next...... strong winds can also temporarily move the feedhorn away from the antenna's focus. Guy wire kits are available which the installer can use to provide additional structural rigidity to the "buttonhook" support if required at the installation."

I had a 1.2m aluminium prime focus dish that worked great, I like them!

Ok, Pete.. I assume that was a quote from someone else.. But you say you like them. I will take that as "this must be a good dish." So a motor should be no problem?