additional reflector beside offset dish?

[steffan_st]

Would it be possible to add just a little extra gain to an offset antenna with 1 or 2 additional reflectors beside it?I realize that it would be very difficult to get the signal in focus at the lnb and I guess the angle would be too tight for getting the signal into the feedhorn,or am I wrong?!?

Just a thought.

 

[rolfw]

Wouldn't make any positve difference, apart from perhaps adding more noise to the signal I'm afraid.

 

[steffan_st]

Wouldn't make any positve difference, apart from perhaps adding more noise to the signal I'm afraid.

Interesting,but why only noise?

 

[rolfw]

It will only add noise because you would be unable to correctly focus the second dish on the correct satellite and also on the feed at the right focal length for the LNB feed, you would almost certainly bring in the signals from neighbouring satellites as well.

 

[steffan_st]

Thank's Rolf!

You know about any tech reading on the net related to this?

 

[rolfw]

Can't recall seeing any steffan, I guess that most people's solution would be simply to increase the size of the dish.

 

[steffan_st]

I know the best solution would be a bigger dish but for a couple of reasons i can't use a bigger one.I was thinking of pieces of a second hand dish to add at the edge of the main dish,know it would be difficult to get the signal from the "pieces" in focus though.

 

[Likvid]

Not possible.

Buy a larger dish instead.

 

[steffan_st]

Not possible.

Buy a larger dish instead.

Is it because the angle would be too tight for the signal to get in to the feedhorn Likvid?

 

[Likvid]

The tolerance is like 2.54mm in Ku-band, it would make it impossible to get more signal, your changing both F/D ratio and electrical characteristics.

IRTE Italy makes dishes, prime focus where you can add panels around it, but that is a completely different thing as all parts are mechanically computed in the manufacturing to string quality to fit each other.

Offset dishes, well i have always hated them as everything is odd working with them, i grew up with prime focus dishes in the 80's and love them, they are so easy to modify the feed system for different types and so on.

 

[steffan_st]

The tolerance is like 2.54mm in Ku-band, it would make it impossible to get more signal, your changing both F/D ratio and electrical characteristics.

IRTE Italy makes dishes, prime focus where you can add panels around it, but that is a completely different thing as all parts are mechanically computed in the manufacturing to string quality to fit each other.

Offset dishes, well i have always hated them as everything is odd working with them, i grew up with prime focus dishes in the 80's and love them, they are so easy to modify the feed system for different types and so on.

But the offset dishes are much more efficient aren't they?I read that you have to have the double size or more on a prime focus compared to an offset dish to get the same gain at ku reception.

 

[Likvid]

Offset dishes are most effecient at smaller sizes.....

Over 1.8m prime-focus dishes are the standard, or even in CATV business where Cassegrain dishes are most effecient but at large sizes like 3.7m and upwards.

I used to have a 1.8m Cassegrain dish, it was nearly as effecient as a ordinary 2.1 prime-focus dish.

Deep dishes are also better but requires excellent feeds, i used to install several Winegard 2.4m and 3.1m dishes which got a F/D of 0.28 compared to 0.40 prime-focus dishes usually have.

The Winegard dishes were made of mesh but the signal wasn't leaking as the holes were within the 2.54mm tolerance for Ku-band.

You had to use Seavey Engineering feeds for those dishes, but they were VERY good and excellent quality.

But the offset dishes are much more efficient aren't they?I read that you have to have the double size or more on a prime focus compared to an offset dish to get the same gain at ku reception.