Dish size question

[Captain Jack]

Hello,

This may seem like a silly question but thought I'd ask anyway. Does the er... "concavity" of the dish matter when it comes to choosing one. We all talk about the surface area of the dish being the important factor - well, a deeper 1.2 meter dish will have more surface area than a flatter one, right? Or is it essentially the outside circumference that really matter, as the amount of signal "entering" the dish will be the same....

Thoughts?

 

[UK Sat Online]

The greater ther surface area, the more signal that is reflected into the lnb

 

[ralphmagno]

hello,
not realy.
most dish builders have done their math .
what matters is size and type.
prime focus
offset
cassagrain
gregorian.

nothing has 100%
lowest is prime focus 55% reflective
offset runs 60 to 65%
cassigrain and gregorian runs 70%

in that area. so a 2 meter prime may run the same gain as a 1.80 offset

and a 1.6 gergorian or cassagrain antenna may run the same as the upper two.

lnb noise fugure and type is important.
most lnb have a test sheet inside like ivacom.
ralph

 

[divibi]

The deeper the dish the better, because you will have less unwanted noise "attacking" your dish sideways!

 

[mouse3]

US Army dishes 90%.

 

[divibi]

US Army dishes 90%.

Hi mouse,What antennas are 90%? What's better than Cassagrain prime focus? We need to know such things for fringe reception.

 

[mouse3]

What brand,i don t know,Soviets are classified.I talk with one guy about this subject and show me one photo about.
This guys work years ago on theat Soviet interceptor Station with 32m dish.
WOW what job,2 weeks maintenace each year and lots of time to test VHF,UHF for fringe using that monster cassegrain.
In the 80-th satelite equipment are not allowed for ordinary people like us here in the Est Block.
The technology it s here since space age,it s not talking about one new design dish,but they are very well polish like the mirrors for telescope.Polish to microns.If the surface of the dish and subreflector it s very accurate under the microscope the gain increase,87-90%.Here it s the limits of technology.

Ask one military dish supplier if you found one to replay about.
Flatter dish have the maximum gain,but perform poor to interference.Deeper dishes are used for terestrial relay stations becose have a norow beam.On satellite DX-ing have sense to use them if the interference it s strong and comes from narrow angle.The dish shape must be perfect to escape from interference.One good example it s C band here in towns 3500 Mhz it s permanently blocked by terestrial relay transmission.
Search on forum what happens in the Cyprus with 26E transmission blocking BBC signals.