Half a dish?

[tonytm]

I've been wondering if anyone has tried to see what they can do with half a dish. The reason for doing this would be that half of a 12' dish would be only 6' tall (and therefore below my fence and out of sight), but would still have twice the effective area of a full 6' dish.

???

Tony

 

[ken2400]

So to try this one would take the 12' and find a way to block the signal from the top half of the dish. Maybe block it at the ring with a piece of metal.
You are on the right track. Out of site out of mind.

Good luck with the cover up.

 

[SatelliteAV]

Interesting concept to purposely discard a portion of a reflector.....

You would need to customize the feedhorn / scalar so not to illuminate the area where there is no reflector. Otherwise, the ground and terrestrial noise will severely affect the signal to noise ratio.

What will happen when the dish is swung East or West? A corner of the dish will rise several feet above the fence line. Maybe cut the straight top edge to be more random and organic so it blends better to the eye?

 

[KE4EST]

That was the first thing I thought of, was that the signal to noise ratio would terrible.

Sent from my Rooted Kindle Fire using SatelliteGuys

 

[tonytm]

Actually I was thinking that the ideal configuration would involve using only the top half of the dish, mounted on a flat platform just a bit off the ground. I generally only watch one satellite, so it would not need to move once pointed. The main difficulties might be:
- Maintaining its shape, when half of the structural elements are missing
- Placing the LNB correctly
- Whether reflections from the ground would interfere with reception? It doesn't seem like they should.

 

[FaT Air]

Trying to re-invent an offset dish are we, inverted at that? Your effective area will actually be less than a 6ft dish. The effective area of an offset dish is = to 2 x 3.14(Pi)R where R= the width. The height of an offset reflector will be greater than the width by a factor determined by the offset angle. Think of it this way- both from the feed, and the satellite, see a perfectly round circle, but is "distorted", physically, by the offset angle involved.
So if we have an offset dish with a height of 6ft, the "effective" width will be less. Maybe ~5ft, right? The actual "effective" width all depends on the offset angle. Therefore, the effective reflector is less than a 6ft diameter. The previous assumes a commonly available feed assembly. A custom designed, and built, feed assembly may be incorporated to illuminate the aforementioned uncommonly proportioned reflector more efficiently. But think the price would be prohibitive.
Put up an 8ft dish, what's 2 ft going to bother if you paint the dish to match the background?

 

[Bongu]

If you could obtain one of the widely available unused 6' offset dishes, your problem would be solved. the 6' commercial dishes have a surface that is much more true and precise than the mesh dishes. They make great fixed dishes also as most only have an Az/El mount standard. A good C-band only LNBF(GeoSat C2?) with a conical scalar would top it off if you do not have a good C-band Ortho feedhorn(would still need conical scalar) handy.

 

[Lone Cloud]

I remember seeing a faux garden umbrella, made with porous fabric (that weed blocking stuff sold at like Home Depot ?) that lets the signal through but looks like it's just there for shade. If you could sew one up so as to hide the dish right under it, and put a picnic table under there, people outside would think it was a barbecue area rather than a dish.

A thought though, if you are committed to cutting a dish to get the height down, I would consider cutting 3 feet off the top and off the bottom. Bigger dish area, lnb still in the middle. I do think you would have to brace the cut ends, however you do it - like pieces of conduit going across and triangulating down and bolted on before you cut.

 

[USDownlink]

This thread reminded me of an oddball dish I frequently pass while driving around, so I tossed the camera in the truck and stopped when I passed it this morning. It sits atop a small utility building in a Pacific Pride station near my home. It's likely their data link authorizing access cards and so forth.

Around these parts, a skew like that and such a low angle off the horizon would mean it's pointed at a bird over the east coast. 72W or 83W, maybe. You can get a sense of what Brian said about a corner of the dish rising tall when swung to an extreme. The dish itself has obviously been there quite a while, what, with all the environmental filth and moss growing on it, but the feedhorn and LNB look fairly new and well maintained. The shape evokes what Lone Cloud says about cutting off the top and bottom of a dish to get the desired height.

Anyway, I guess the point is someone actually commercially made "half a dish", and there are feedhorns designed for such. Other than the pictures, I don't have any more information. Maybe someone here will recognize something about it.

 

[tonytm]

Thanks all for the comments. I don't think we have the math quite right, as it is not quite the same as an offset dish, but I agree that it would be much more practical to simply go with an 8-footer. If one can be found! After a couple of hours of searching I only found one for less than $300 (not including shipping).

By the way, while looking around the web for clues on this I found a long thread on techniques people have used to make their own dish:

Anyone tried to make BIG dish at home?

 

[ynnedibanez]

what about just buying a cheap 6' c-band dish?

C Band Satellite Dish | 6 foot Prime Focus Dish 180cm 6' C Band satellite dish cku dish Antenna

 

[eurosport]

This thread reminded me of an oddball dish I frequently pass while driving around, so I tossed the camera in the truck and stopped when I passed it this morning. It sits atop a small utility building in a Pacific Pride station near my home. It's likely their data link authorizing access cards and so forth.

Around these parts, a skew like that and such a low angle off the horizon would mean it's pointed at a bird over the east coast. 72W or 83W, maybe. You can get a sense of what Brian said about a corner of the dish rising tall when swung to an extreme. The dish itself has obviously been there quite a while, what, with all the environmental filth and moss growing on it, but the feedhorn and LNB look fairly new and well maintained. The shape evokes what Lone Cloud says about cutting off the top and bottom of a dish to get the desired height.

Anyway, I guess the point is someone actually commercially made "half a dish", and there are feedhorns designed for such. Other than the pictures, I don't have any more information. Maybe someone here will recognize something about it.



View attachment 75776View attachment 75777

I want one of those just 'cause they look cool!

 

[putney]

you can probably talk him down..8' and 10' !

C band sattelite set up

 

[tonytm]

Thanks for that link putney! I spoke to the owner and he is willing to let the 8' mesh go for $85. Hard to estimate the condition - it's been sitting (unmounted) for some years. I'm thinking it should buy me at least 3 dB over my 6' solid? The 10' would also be a good score but it has to be removed from the roof. I will take a look at it tomorrow.