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View Full Version : Non-standard dish mount/orientation question


mbklein
05-14-2006, 11:32 PM
Hi everybody. I've been experiencing problems with my DirecTV dish since I moved here, and I'm looking for a little advice on straightening it out. I've installed five dishes myself at various locations, so I'm comfortable with the aiming process. It's a regular 18" Phase I single-LNB-arm elliptical dish. No high def or Para Todos for me, and my locals are on 101, so the simple dish is just fine.

Because of many large trees in the neighborhood, there's only one spot on my entire property that I can get any signal at all without resorting to an unacceptably long pole. (I say "unacceptably" because aesthetics are important to me, not because of any neighborhood restrictions.) It worked fine all winter, even through snowstorms, but once the tree next to my house leafed out, we've been in signal fade hell. At best we get minor pixellation; when it so much as drizzles, we get nothing. I know the "look 10 degrees higher than you think you should look" rule when it comes to finding obstructions, and I believe I've identified the leafy bits in question.

I can't alter the tree. I've already done so as much as my neighbor (who owns the tree) will let me, and besides, the offending limb is 33 feet off the ground, and I can't jump that high. I can't pole mount the dish in the yard because I live so far north that the low aiming angle requires me to mount the dish at least 10-12 feet off the ground just to get over my neighbor's house.

I did some more eyeballing tonight, and I think that I could get line of sight around the tree if I turned the mounting foot at a right angle, so it was extending beyond the edge of the house by another foot or so. I've seen dishes mounted sideways and at other angles before, but I've only ever dealt with a plumb vertical pole.

My question is, how hard is it to aim a standard 18" elliptical dish when it's mounted sideways? Are there any good tricks? I'm not going to have the benefit of the elevation guide on the dish (as rough as that is in the first place), so I feel like I'll be more or less blind in two directions instead of starting with a close-enough elevation and scanning horizontally. Also, what is the change in the dish's orientation (with the major axis horizontal instead of vertical) going to do in terms of signal strength/rain fade?

(Yes, I've also thought about trying a 24" dish, but my wife, who holds aesthetic veto power, isn't willing to go that route. Besides, I don't think a bigger dish will do me any good until I can get a consistent signal with the sun shining.)

Last question -- I almost always have a stronger signal on even transponders than on odd, independent of which LNB output I'm using, and even when I swap out cables (so I don't think it's a cabling issue). Could this be explained by the LNB not being aimed exactly on-center? It feels a little loose sometimes, and it can jiggle around in the end of the arm. I'm planning to tighten it up when I move the dish, but I'm curious as to whether that will actually solve that part of the problem.

Thanks,
Michael

Want1394
05-15-2006, 11:23 AM
You must mount the dish vertical. If you look at any of the aiming diagrams, the physics of the signal collection is clear - the signal arrives at the dish approx. 23 degrees above vertical and the dish focuses the beam on the LNB about 23 degrees below vertical. Remember high-school - angle of incidence = angle of reflection. You can mount the dish where you want - just build a brace extending out so you can mount the dish vertical.

And the dish is round, not elliptical - it's only got one focal point since it's only picking up one satellite signal.

If you don't have a cable problem and have significantly stronger even than odd transponder signals ( >10 points ) you probably have a bad LNB - aiming has nothing to do with it.

Most situations with tree problems can be helped with a mounting on the roof of the house, but that depends on the house, trees, etc.

JimSpence
05-15-2006, 01:15 PM
Have you thought about going low? Mounting the dish near the ground and aiming under the problem tree? How about the other end of the house or a pole mount away from the tree?