For a given size which is better, parabolic or offset?

Artist 2004

A shopkeeper told me that a 150cm offset dish gives the same reception as a 200 cm parabolic. Is this true?

rolfw

I doubt whether a 1.5m offset would out perform a prime focus of simialr quality, the only disadvantage of the prime focus being slight shading of the dish by the LNB and support arms.

Rolf If you enjoy our site, you can help support it by wearing our unique branded merchandise, you can do this by clicking on my baseball cap, making a direct donation with Paypal by clicking on the Donation button below, or using our site supporting advertisers, to do this, click on the central image below. Follow us on Twitter, click on the twitter image.

dig deep

Every BIG dish is gregorian so I think I bet my "dollar" on Rolfw´s answer
The offset is easier to mount on a wall that is a good reason for using them, not that they are better in any other way

Artist 2004

Thanks, both. While I've got your attention, what is the convention for stating dish size for an offset dish? My "120" cm dish is something like 112cm tall and 105 cm wide...

spiney

If possible, then an offset dish would always be better. Because, with prime focus dishes (including Cassegrain, etc), various bits "block" part of the radio "beam" falling on the reflective surface.

This effect varies, with dish type, so no "general formula" is possible.

As dishes get bigger, the offset type doesn't have enough mechanical stability, ie, the long lnb pole and dish surface would flex too much, putting the lnb "off focus".