פורום הלווינים והטכנולוגיות הישראלי

קוד: בחירת הכל

How to you measure a satellite dish?
A prime focus satellite dish should be a perfect circle. To measure the size of a prime focus dish, stretch a measuring tape staright across it and note the measurement. Do not measure the valley!!! Also, the edge or lip of a prime focus dish does not count.

An offset dish can be tricky.
Most fta offset dishes will be shaped like a diamond, and they will have a long axis and a short axis. Dish size on the diamond offset dishes are supposed to be equal to the short axis measurement.


Some vendors measure the valley of the dish and try to fool you into thinking you are getting a bigger dish than you really are. Other vendors will use the long axis in their dish advertisement to fool you on the dish size.

Then there is the gain game. Almost all antenna vendors play games when it comes to how well a dish antenna should work.
Gain in db(d) or dbd will be antenna gain as referenced to a dipole.
Gain in db(i) or dbi will be antenna gain as referenced to a theoretical isotropic antenna. This antenna only exists in theory and it will have a couple of db gain over a dipole antenna.

Some vendors only reference the dish gain in db. You can't sue them for falsely advertising dish gain because they don't tell you what antenna they are comparing the dish to.
The last db trick is to measure the dish gain at the high end of the usable band for the dish. They do this because the db gain will always be more at the higher frequency than at the lower frequencies.


Other offset dishes may be more of a rectangular shape, especially if they are used for receiving multiple satellites. You may also need a lnb with a feed horn designed specifically for these rectangular shaped dishes if you are going to get the full benefit of its dish area. These types of offset dishes are usually designed for a commercial provider so the specs on them are hard to get