Missing Center-KU problems?

[key2way]

Hello
I have my 8' Alcoa dish and I am having problems with KU band.
There is a center cover missing on the dish, would that cause the loss in signal on KU?

Been tweaking the dish and C band is great but KU is lacking.

If I filled the hole would that make my signal any better??

Here is a pic:
SatelliteGuys Photo Gallery - P5240010 - Powered by PhotoPost

It's directly below the ALCOA logo in the center.

thanks
John

 

[B.J.]

Hello
I have my 8' Alcoa dish and I am having problems with KU band.
There is a center cover missing on the dish, would that cause the loss in signal on KU?

Been tweaking the dish and C band is great but KU is lacking.

If I filled the hole would that make my signal any better??

Here is a pic:
SatelliteGuys Photo Gallery - P5240010 - Powered by PhotoPost

It's directly below the ALCOA logo in the center.

thanks
John

None of your usable signal hits that hole. The hole is blocked by your feedhorn. So it makes no difference at all.

 

[key2way]

None of your usable signal hits that hole. The hole is blocked by your feedhorn. So it makes no difference at all.

Ok thanks B.J.

I did some test and seen some difference in the 2 dishes.
---------------------------
AMC-9 11775 H

8' Alcoa / DMX741
Signal:100%
Q: 77-78%

4' Channel Master QPH-031
Signal:84%
Q: 79-80%
---------------------------

I have tried 4 different LNB's on the 8' and all were the same.
The string test (I used every panel) and they all just touch in the center.

I guess I will try some other things.

Thanks
John

 

[Anole]

The dual-band LNBFs, such as the BSC621, Ck-1, and DMX741, all are tricky to setup for Ku.
First, their Ku LNB only sees the middle of the dish, not the entire surface.
That cuts performance somewhat.
(your center hole has no effect, as B.J. noted)

The fact that the Ku probes are recessed inside the feedhorn, may contribute to the adjustment difficulty.
From what I've seen, you need to get the LNBF centered perfectly on the dish.
Next, you need to have the LNBF point directly to the center of the dish.
Those who are careful, seem to have good results.
There are plenty of reports by members who have been successful.
However, "close" is not close enough.


If you are unsuccessful, another approach which seems more easily tuned up, is the orthomode feedhorn.
Here are two examples by ADL and Chaparral.
Both are expensive, and need two C and two Ku band LNBs, plus a multiswitch.