Satellite Alignment - What angle?

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727 posts

Ultimate Geek

#584538 21-Feb-2012 13:54

Well, by literal back of envelope calculation, and relying on a vague recollection of the sine rule, I reckon that the plane of the dish will need to be tilted to an angle of 65.4 degrees from the horizontal for the "beam" to be horizontal.

That seems plausible. I'll check my figures.

Mind you, that may be for a spherical egg in a vacuum of course. ;)

RunningMan

8965 posts

Uber Geek

#584563 21-Feb-2012 14:18

Jaxson: Mate, just grab a builders level and put it across the face of the dish, forget the offset aspect. Get the face level and attach your wifi receiver down where the lnb was on the arm.

I would have thought that would end up with your target point sitting up in the sky by a few degrees - the LNB (focal point) would be below the horozontal axis, so the point it's aiming at would be above. You'd need the face of the dish to actually be angled down below horizontal.

If it was a prime focus dish, with the focal point dead centre of the axis, then the face of the dish would be vertical, but I think the OP's using an offset dish - with these, the face of the dish isn't actually pointing at the satellite, it points a bit below.

The OP's idea of setting the scale on the mount to [say] 20 degrees, then leaning the pole over a further 20 degrees should get it about right.

When you look at it side on, it will look like it's pointing below horizontal, but the point of aim should be level.

Of course, it may just be quicker to stick the WiFi transceiver where the LNB goes, then just start pointing the dish by hand, and watch the signal level - it'll most likely be the quickest way!

RunningMan

8965 posts

Uber Geek

#584576 21-Feb-2012 14:30

Here's a pic that hopefully demonstrates a bit better.

It's not my picture, it's courtesy of TechTir Magazine

Jaxson

8044 posts

Uber Geek

Trusted

#584589 21-Feb-2012 14:55

RunningMan: Of course, it may just be quicker to stick the WiFi transceiver where the LNB goes, then just start pointing the dish by hand, and watch the signal level - it'll most likely be the quickest way!

Yeah that's where I was coming from, as in use the level to give you an idea of where you really are (as your scale isn't going to adjust right down to zero or below degrees). This should put you close to the ball park, though not perfect as you've nicely illustrated. I reckon just try it and then if it really doesn't work do a lot more homework and calcs.

grant_k

3539 posts

Uber Geek

Trusted

#584595 21-Feb-2012 15:07

Given that there is such an angle between the apparent view of the dish, and the actual view, another approach would be to turn the dish upside down on its 4 mounting bolts. Looking out the window at our Sky dish, there doesn't seem to be any reason you couldn't do this. The dish would look a little strange with the LNB mounting arm on the top rather than bottom, but at least the dish would still look as though it was pointing upwards, meaning that you wouldn't have to tilt the hockey stick mount at all. Achieving horizontal view should then be possible within the normal adjustment range of the dish -- 20 to 70 degrees according to the scale on ours.

Printertech

81 posts

Master Geek

#584653 21-Feb-2012 16:10

Why not mount your transmitter on the dish, download WiFi Analyser onto your smart phone, then stand at the receive position with your smartphone while somebody tilts the dish for the highest signal?

oxnsox

1923 posts

Uber Geek

#584864 21-Feb-2012 22:26

Tilt Dish down some.
Place your Laser at the point you're putting the wifi
Place a piece of paper (or cardboard) behind the laser and you may be able to see the reflected dot some distance above it. (if not polish center of dish to remove oxidisation film and grime)
Adjust the dish down/up to get the reflected dot running approx level with the roof-line.
Remove laser, adjust azimuth to aim at the person who's wireless you're borrowing

Sharesies

Trade NZ and US shares and funds with Sharesies (affiliate link).

xarqi

727 posts

Ultimate Geek

#585040 22-Feb-2012 10:52

oxnsox: Tilt Dish down some.
Place your Laser at the point you're putting the wifi
Place a piece of paper (or cardboard) behind the laser and you may be able to see the reflected dot some distance above it. (if not polish center of dish to remove oxidisation film and grime)
Adjust the dish down/up to get the reflected dot running approx level with the roof-line.
Remove laser, adjust azimuth to aim at the person who's wireless you're borrowing

Or... attach a small flat mirror to the inside of the dish (it doesn't actually matter where), put your laser pointer where the LNB would go, and direct it to the mirror. Adjust until the reflected beam picks out your "target".

eXDee

4032 posts

Uber Geek

Trusted

#586169 24-Feb-2012 11:39

xarqi:
oxnsox: Tilt Dish down some.
Place your Laser at the point you're putting the wifi
Place a piece of paper (or cardboard) behind the laser and you may be able to see the reflected dot some distance above it. (if not polish center of dish to remove oxidisation film and grime)
Adjust the dish down/up to get the reflected dot running approx level with the roof-line.
Remove laser, adjust azimuth to aim at the person who's wireless you're borrowing

Or... attach a small flat mirror to the inside of the dish (it doesn't actually matter where), put your laser pointer where the LNB would go, and direct it to the mirror. Adjust until the reflected beam picks out your "target".

I like this idea. It could work nicely, i knew the laser could come in use.
Also as for borrowing WiFi, its a WISP in fact, although with such a setup you could do some interesting wardriving

Printertech: Why not mount your transmitter on the dish, download WiFi Analyser onto your smart phone, then stand at the receive position with your smartphone while somebody tilts the dish for the highest signal?

The latest Ubiquiti firmware has an 'antenna aligner' feature which is simply a very fast updating signal strength meter. Wifi Analyzer is an excellent app, but i think i'll use this plus the laser for aligning.

Or the alternative is they might decide to mount the receiver in a tree instead of using the dish

Jaxson

8044 posts

Uber Geek

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#586182 24-Feb-2012 12:05

Mate if you can fit a laser somewhere in there then do it. I mean, what's not better with green laser attached to it?

kiwirock

685 posts

Ultimate Geek

#586286 24-Feb-2012 14:49

I find it hard to believe you can't get a good signal out of a NanoStation Loco 150 metres away. Have you tried them on channel 13, and they're outside looking at each other?

I have an old NS2 and it works about 2-3KM down the road with my iPod.

Be aware, the Loco output is about 100mW and has an 8dBi intergrated antenna. If your's is similar, that's 600mW E.I.R.P. If you put that on a dish, you need to work out what dBi gain the dish will add, Ku about 33dB but at 2GHz probably not a huge amount. But I would say enough to make the E.I.R.P well above 4000mW, which makes it an illegal transmitter if it's any higher.

I suggest you work out the gain at 2.4GHz if you're using 2.4GHz, and not 5.8GHz, and do the math before setting out break the law.

You'd also need to mount the loco so it's intergrated antenna is at the focal point of the dish on the LNB arm or you're going to end up wasting the whole purpose of using an offset dish. A few mm's out of alignment and you're talking a lot of dB's of gain lost.

Cheers,
Gavin.

edit: You'd probably be better mounting the dish upside down too, so it doesn't have to tilt so far. Otherwise it'll be near 45 degrees down otherwise.

eXDee

4032 posts

Uber Geek

Trusted

#586299 24-Feb-2012 15:24

Jaxson: Mate if you can fit a laser somewhere in there then do it. I mean, what's not better with green laser attached to it?

I wholeheartedly concur :D

kiwirock: I find it hard to believe you can't get a good signal out of a NanoStation Loco 150 metres away. Have you tried them on channel 13, and they're outside looking at each other?

I have an old NS2 and it works about 2-3KM down the road with my iPod.

Be aware, the Loco output is about 100mW and has an 8dBi intergrated antenna. If your's is similar, that's 600mW E.I.R.P. If you put that on a dish, you need to work out what dBi gain the dish will add, Ku about 33dB but at 2GHz probably not a huge amount. But I would say enough to make the E.I.R.P well above 4000mW, which makes it an illegal transmitter if it's any higher.

I suggest you work out the gain at 2.4GHz if you're using 2.4GHz, and not 5.8GHz, and do the math before setting out break the law.

You'd also need to mount the loco so it's intergrated antenna is at the focal point of the dish on the LNB arm or you're going to end up wasting the whole purpose of using an offset dish. A few mm's out of alignment and you're talking a lot of dB's of gain lost.

Cheers,
Gavin.

edit: You'd probably be better mounting the dish upside down too, so it doesn't have to tilt so far. Otherwise it'll be near 45 degrees down otherwise.

I can't change the channel, direction or location. Its a WISP. I Believe they are running an omnidirectional antenna.
Currently between the nanostation loco and the AP is many branches of a tree, and then the signal has to clear some buildings across the road. Aside from the tree, while there is 150m line of sight to the AP but it is over buildings roofs and these easily intrude on the fresnel zone.

Currently its signal fluctuates from -80dBm to in the -90s before dropping.

the EIRP will be adjusted on the nanostation as necessary, theres a nice output power adjustment on the nanostation. By dropping this an making it more directional i believe i can improve the signal quality.

Shows the internal antenna. 2nd one down. Larger here: http://www.flickr.com/photos/mattw/3460097815/sizes/l/in/photostream/

Thanks for you input!

kiwirock

685 posts

Ultimate Geek

#586382 24-Feb-2012 17:36

Narrowing the beam by using a dish would also help to reject interference from the side and back of the antenna, not just boost the signal.

Your WISP needs to upgrade the client if it's marginal. If you're paying for it that is. You really need a good 20dB for fade margin I've found. The Airbridge TDMA series look better too, more suited to a client radio than the loco.

eXDee

4032 posts

Uber Geek

Trusted

#586756 25-Feb-2012 18:34

Nah they are just providing a public WiFi service, theres no SLA or anything.

kiwisat

147 posts

Master Geek

#586805 25-Feb-2012 21:27

If you use the lnb support arm as your pointer you will be fairly close.

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