Adding sidecar FTA LNBF to Shaw subscription dish

[polgyver]

For some time I was curious if such a setting would work. Today's trial is not conclusive : while some stronger transponders from 97 W (Galaxy 19) allow for watching programs, weaker transponders are not very reliable.
The main reason is that added sidecar LNBF is much off-axis.
Another reason, added LNBF has round "Field of View", and changing its scalar is needed.
Has anybody tried to custom-made scalar for such a purpose?
Seven pictures (some annotated) follow.
Cheers, polgyver

 

[danristheman]

What are you trying to get using the sidecar lnb on that dish? I think when you use a round lnbf on a oval dish your only most of the dish. Oval lnb to oval dish, round lnbf to round dish.

 

[polgyver]

What are you trying to get using the sidecar lnb on that dish? I think when you use a round lnbf on a oval dish your only most of the dish. Oval lnb to oval dish, round lnbf to round dish.

Good question.
First, to investigate if it is possible to modify the scalar specifically for LNBF designated to be "OFF AXIS". To "catch" ALSO the rays which - due to coma- are missing the LNBF, passing by.
As the next photos show, reflected "off axis" rays form "unshapely", larger focal cloud.
Secondly, despite hundreds of programs provided by subscription, some programs probably are not available there, like ethnic programs, or other, like Ebru, RT or Smile of a Child.

 

[bmk]

Hello polgyver,

I have modified an LNB with a round field of view for an oval shaped dish (Directv Slimline), see attached photos. Before modification, RT on 97w was 40-41% signal quality, after, it was 52-53%. This is successful enough for me. This is almost as good as my winegard 76cm dish, which gets RT with 57-58%. The winegard number seems low to me, but it does not fade much in the rain, and it is watchable down to 35% signal quality.

This modification was based on intuition and luck, I didn't even measure, just ten minutes with a hack saw to see what happened (I didn't really care if it was a failure because it was a cheap $7 lnb). I simply cut notches in the outermost ring of the scalar, approximating the area where the dish is widest. I know that the LNB now sees the widest bits of the reflector because I can watch signal quality drop when I cover them with my hand, and it didn't do that before. Since this modification, someone posted a link to a document about feed horn and scaler design in the C band forum I think, take a look.

Brian

 

[polgyver]

Hello, Brian,
You did very interesting experiment. I just wonder if - instead of removing some scalar ribs - the same could be achieved by adding (building up) some metal semi-circles above and under the LNBF's inlet?
In a few minutes I have to leave town for 3 days, so, let's be in touch next week.
Cheers, polgyver

 

[FaT Air]

Removing some of the scalar is what I also 'had in mind'
"Building up' would narrow the 'field of view' where removing widens it.

 

[jorgek]

What about just moving the LNB back a bit?

 

[Titanium]

Moving the feedhorn opening away from this sweet spot, these reflected signals signal will no longer merge and enter the throat. The reflected signal convergence point is fixed. If the scalar is also adjustable, then the feedhorn opening can be optimized separately from the scalar optimization.

 

[polgyver]

Tinkering takes more time than expected...
Following Dan's suggestion, I just made flattened "funnel" (oval LNB to oval dish).
Also prepared scalar with some grooves removed (as done by Brian)
Placed plastic ring in front of original Shaw LNBF, for better orientation of substituted other LNBF's.
Planning to compare other scalars to see, which one works best.
Blind scanned Anik F2 (111.1 W) with original Shaw LNBF, and I got 2 channels In The Clear.
Live video of Hamilton Beach, but what's the frequency? 4 digit, is it C-band?

 

[FTA4PA]

If you're getting the Huntington Beach cams then it's aimed at 103W. I have those two scanned in at 11942 V 20000 on KU band.

 

[bmk]

Hello polgyver,
In the image you posted with the various scalars/feedhorns that you intend to try, the one labelled "scalar from other, elliptical dish" is very similar to a scalar that I saw which was the inspiration for the modified lnbf that I tried. I do not recall what dish the scalar I saw came off of, but I know there are some primestar and globecast world lnbfs with scalars that look similar.

Brian

 

[SatPhreak]

You have your LO set to 5150 & it is 10750 for a Starchoice dish.


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[polgyver]

Oops... again, I mis-pointed the dish (the previous instance was dish inside the room, pointed to 123 and assumed to be at 125 W).
As usual, vigilant forum members noticed it and thanks to them, correction could be made.
However, after moving the dish more to West (from 103 to 107.3 ) the distance between original LNBF assembly and sidecar LNBF has increased significantly.
This makes the whole idea not feasible (unless, some magic scalar with feed is invented for gathering all the dissipated "rays" resulting from far-off-axis position).
Another sub-topic, which has emerged, (modifying round LNBF to elliptical - or - panoramic - dish), is still worth pursuing, though.
More info on pictures (some annotated).
Oops, again, now there is a problem with uploading my files (photos)...
So, maybe later ...
Cheers, polgyver

 

[polgyver]

I had to log in again.
Now - photos:

 

[Soniconyourroof]

It is amazing how well those oval dishes work.

 

[polgyver]

It is amazing how well those oval dishes work.

They work well thanks to their rigidity, improved by plastic "ribs" on the back, so they focus quite precisely.
Less vulnerable to distortions than metal round dishes (as metal dishes' stiffness is achieved by their edges only).
But their "oval-ness" does not contribute in any special way to signal quality.
Any shape, even Maple Leaf, will work, providing, that its surface belongs to paraboloid of rotation.
Cheers, polgyver

 

[Cham]

Wonder how a horn antenna (kind of like a funnel, sometimes used instead of a primary reflector) would work in place of a scaler ring for collecting out-of-focus RF in this sort of side-car application? At least for Ku the "funnel" wouldn't have to be that large in diameter. Might have to do some fabricating though, looking through the hardware sections these days most funnels for fluid transfer are plastic these days, but maybe tin foil could be added to the inside... or conductive paint... Might be able try this without removing the existing scaler ring if it can fit over the initial feed horn.