The Wireless Internet Cantenna gets Dished

Step 5 Business Time

I forgot to get screen shots or any of that. I'm noticing that the dish is picking up a weaker lobe to either side of the same signal, found by rotating the dish 360 degrees. I think it's the cantenna receiving directly to the side, skipping the dish. Those ring things might fix that.

I got a small improvement though. I counted 70 networks total, but most are weak signals or just don't connect. Now my friends think I'm extra serious! Only now, they think I can watch HBO on my laptop. I sure hate to ruin the image, I just told them I didn't want to pay for the premium channels! Honest! I'm not hacking into any satellites!

Comments

[obese1konobe]

Looking at your side on photo, if that is how you actually direct the dish the 'beam' it is receiving is about 20 degrees below the horizon. As its an offset dish (oval) its designed to collect the signal without being interfered with by the feed. Best way to check is to look at the dish from its tagrget and have someone tip it back to the sweet spot, thats when the oval shape appears to form a circle - you are then directly in its beam!! Hope that makes sense, and if you already knew all that sorry again.

[Shadetree Engineer]

You have the right idea. Assuming the chimney top is flat level, 20° is about close enough. The body of water you can see in the background is where I was aiming, at one of the buildings on my side of the water. I've heard elsewhere that an offset dish is really just an oval section taken from a standard parabolic shape, the center of the offset dish being also the center of a comparable center-feed. It's a compromise that ignores some small signal losses in order to make the dish as small as possible. I've also made another compromise by placing the can so that it catches background radiation. It would be better to have the can aimed upwards so that it's 'peripheral vision' as it were would only have the open sky past the edges of the dish. As you can see, I took the easy assembly route...

[obese1konobe]

Heres a question. What would happen if you put the feed smack bang central?? I know you would get losses from blocking but would the 'beam' be straight or would the beam converge to a point?? Is there a simulator that could show this?

[Shadetree Engineer]

The dish I used checks out with the method of construction that the factory guys use. It really is just a standard parabolic reflector that has been cut into an ellipse. If a feed should be mounted dead center on this offset dish, the result will be about the same as taking a center-fed dish and cutting most of it's reflector off. Providing that you get the feed at the right distance for the focal point, the beam coverage will be at a long distance, but most of the signal is going to be lost. You can usually count on a noticeable portion of the outer edge of the reflector as not useable on any type of dish. That's normally not a problem as the dish will be built to compensate for this. The important thing is that the area that is used for reflecting most of the signal is very marginal with a little dish like mine. Blocking any of that central area will have a big effect.