Satellite Dish actuator/mounting and controller

[CLUELESS1]

Has anyone experience on actuating a Satellite dish to cover several Satellites. I have a ground fixed pole mounted motorized dish. Unfortunately it has to be removed due to trees being felled nearby.

I want to reinstall it afterwards, but as the trees have been causing subsidence, there is a chance the ground will move afterwards making it possibly need mechanically readjusting all the time. I have seen an alternative to the verticle pole, where the dish is placed on it's back on a horizontal turntable on the ground. The turntable is rotated, while the angle on the dish is pushed up/down by a linear motor piston type motor. The version I saw had a dome over the assembly resembling a radar scanner cover on a warship.

Just wondered if anyone has done such a project. Ideal for rooftops where you want to conceal a dish.

 

[goom]

Your rooftop should be a stable platform so should not need to be adjusted once set up. In my view, multiple dishes for multiple satellites is the way to go. Simpler and probably cheaper. You would need a readily available switch, controlled by your receiver, to select the appropriate dish for the service that relates to the appropriate satellite.

 

[CLUELESS1]

Thanks Goom, I am going to mount it on the ground. I already have it connected to my receiver using USALS! but as it has to be moved, and the ground is going to re settle (2 large Oak trees coming down, clay ground), I thought I could mount it on it's back and have tweekable pan/tilt (steppers - Picaxe control - some method of memory of azimuth) then the ground can do what it likes. Might need adjustable horizontal adjustment of rotating base. Anyway, just wonder if anybody has been down this road and idendify problems up front.The commercial unit I saw was a little out of my pocket 10k plus pounds

 

[AllyCat]

Hi,

All the "broadcast" (communications) satellites are located above the equator so it is normal to use a single motorised "equatorial mount" which moves around an axis approximately parallel to the Earth's axis (i.e. pointing north, about 52 degrees from the horizon in the UK). However, the satellites are not at "infinity", but only about 40,000 km away, so it's not quite the same as an astronomical mount.

To accommodate "random" movements, you would need an "Az-El" (Azimuth - Elevation) mount with two motors and quite complex software to control them. For example, finding a "maximum" signal is easy when swinging around one axis, not so easy with two "degrees of freedom".

Generally a dish (outdoors) is far too heavy to use a stepper motor, but it is possible to move the LNB (antenna/amplifier) a few degrees, but the gain (i.e. signal amplification) drops as it's moved away from the focus of the dish. In extreme cases, the "skew" also may need to be considered, which is the rotation of the plane of polarisation of the microwave signals.

So, as said above, a "stable platform" is likely to be a better solution. The beam width required for typical broadcast satellites is a degree or two, so not seriously arduous.

EDIT: IIRC there was some consideration being given (with USALS/DiSEqC) to allowing "old" broadcast satellites (i.e. with little remaining thruster fuel) to drift a few degrees away from their equatorial orbit. The problem is that if it is a few degrees "high" at noon, then it will be a few degrees "low" at midnight. Thus the dish (or more likely the LNB position) needs continuous "active" control and I don't know if it was ultimately considered to be a worthwhile feature.

Cheers, Alan.

 

[CLUELESS1]

Thanks Alan, useful points.

I cannot find the larger dish version, but this was the similar type of project I had in mind.

http://www.megasatuk.com/campingmangps.html

Because I have been told by satellite installers I might need regular visits to realign the dish because of ground settlement after large trees are removed, I started thinking of alternatives where I could tweak settings electronically. I saw a diagram showing how the signal gets into the LNB in conventional mounting, but also saw it would still work with the dish on it's back. I get what you say that the skew of the LNB gets corrected by the geometary of the USALS/DISEqC motor shaft, so that would have to be catered for. It's a shame the dish cannot be held stationary and the LNB moved round in a hallf circle (or maybe it would work?)

Being a circular dish (not eliptical)

Regards

 

[bluejets]

I saw a diagram showing how the signal gets into the LNB in conventional mounting, but also saw it would still work with the dish on it's back. I get what you say that the skew of the LNB gets corrected by the geometary of the USALS/DISEqC motor shaft, so that would have to be catered for. It's a shame the dish cannot be held stationary and the LNB moved round in a hallf circle (or maybe it would work?)


Regards

Doesn't work like that.
Look for dish alignment and you'll see why.
an example here .......... http://www.satsig.net/pointing/elliptical-antenna-orientation.htm

 

[CLUELESS1]

Thanks. One of the "On it's back" modes I saw here

http://www.youtube.com/watch?v=Std8QuEBV8U

 

[AllyCat]

Hi,

I think that YouTube video has the dish "on its back" because it's being used near to the equator! The campingmangps device appears to have a more conventional slanted "dish", but enclosed within a weatherproof "raydome".

The "dish" is basically a reflector similar to an optical telescope, so it has a focus where the "viewer" (eyepiece or LNB) needs to be located. However, the demands of a satellite radio signal are less than an optical telescope, so the dishes often have an "offset focus" so that the LNB is not in the direct "line of sight" of the dish. In northern latitudes, it also allows the dish to be almost vertical, causing rain and particularly snow to fall off.

The "beam width" depends on the diameter of the dish (relative to the wavelength) so another "trick" employed for satellite antennas is using elliptical dishes. They have their larger axis (narrower beam width) horizontal, to select between the many satellites (perhaps only a few degrees apart) around the equator. The smaller vertical axis gives a wider beam width (to accommodate some vertical drift of the satellite) and to make the dish smaller (cheaper and less of an eyesore).

Of course satellite dishes often can be mounted low on the ground, because they only need "line of sight" to a satellite reasonably high in the sky. But in your case it seems more appropriate to attach the dish to a stable wall, or to manually adjust the LNB occasionally if the signal does drop due to movement, rather than attempt any type of automated control.

Cheers, Alan.

 

[CLUELESS1]

Thanks again Alan.

I did find an article on the internet which I cannot find again. It showed the beam deflection from the dish to the LNB in both conventional mount and on it's back showing no difference between the two. I think I will put any ideas on hold until I get a spare dish/LNB to play with. The YouTube video makes it look a very convincing workable alternative especially if people are wanting to hide a dish.

Never mind, something to think about later. Thanks for your input.

 

[CLUELESS1]

Sorry Bluejets, forgot to say thanks for your information. I am using a round dish as I read somewhere the oval dishes are designed primarily for 28.2 (Sky Channels) and not so good for other satellites.
I will wait until I win a smaller dish than my current 1 metre one and then have a further attempt at seeing what happens.

 

[bluejets]

I think you need to address a satellite dish forum as the actuactor is simply a positioning mechanism.
As explained before, the dish is placed in the arc for the Clarke belt and then positioned on your satellite from there.
No need for any picaxe as I can see.
As to a smaller dish, I doubt that would work as certain satellites require minimum size dish depending on both your location and satellite position, whether C band or KU band.

 

[CLUELESS1]

Thanks again bluejets, I will look around at forums. If it works with a smaller dish 60cm, I will try belt driving its rotation with a stepper and its elevation/azimuth from a screw driven stepper. I will use the Picaxe to do a programmed rotation/azimuth cycle until it finds a satellite/s . If it works then I will look at how I store positions. Will treat the project as a llearning curve.