Selfsat HH90 useless for Selfsat H21D?

[Davor]

I am planning to by the Selfsat H21D and Selfsat HH90 motor. Question I want to ask here is, whether the HH90 motor on H21D has any use. Here is my reasoning that it has no use:


The dish is small, so an accurate setup is mandatory. This means skew and elevation must be as accurate as possible. But when one looks at satellites (0°E to 72°E ) for Europe, then the corresponding dish elevation ranges from 5° to 31°, and skew from -36° tot 3°. Now, the motor only lets me adjust the azimuth, but not the elevation and skew, which means that if I watch something on Hotbird (13°E), and want to switch to Eutelsat W5 (70.5°E), I would need to adjust the elevation and skew some 30°, and azimuth some 60°. Motor will, of course, handle the azimuth, but what will adjust the elevation and skew? Because of the size of the antenna, and especially the flatness, I tent to conclude that the motor is somewhat useless for this “dish”. Or am I wrong, and is the motor designed in such a way that it automatically can change the skew and elevation when it turns?

Am I right, or wrong? Hope someone can clarify it to me.

Kind regards,
Davor

 

[Lazarus]

Don't worry - the locus of the Motor is designed to alter automatically the effective Dish Elevation and LNB Skew right across the arc!

Basically, all you do is physically set the Skew to zero when the Dish is pointing due South from you and you never have to touch it again.

Also, if you observe any H-H Motor tracking a Dish across the arc, the Elevation is at a peak for your South Satellite and the locus described by the Motor Stub/Dish ensures that the Elevation decreases appropriately as you track further East or West from South.

You will also observe that the Dish "leans" as it tracks towards the edges of the arc ,which neatly accommodates the desired Skew.

How big is the Dish, anyway? As a general rule, the larger the Dish, the narrower the Beamwidth, and the greater the need for precision. Smaller Dishes have a wider Beamwidth (and less gain), so precision is less important for the strong Satellites (although the flip side is weaker Satellites being unavailable).

Edit: Just Googled and ascertained that the Dish is a teeny flat plate design, but although performance may be worse than a "proper" Dish, similar principles apply - provided, of course, that you can actually clag a Motor on to it ???? (Can't really tell from the pic I'm looking at)

What Satellites are you hoping to catch with it?

Personally I wouldn't motorise such a Dish, but there are plenty of folk who take pride in doing such things - eg Sky Zone 1 Minidishes! It seems to me this particular Dish lends itself best to single Satellite use.

 

[Davor]

Thanks for the fast reply Tivù.

Indeed, the dish is very small (566×300×65mm). Here is the official link: _http://i-do-it.co.kr/ And yes, one can put a motor on it.

We need just that one dish, because we have to think about the looks of our building. Women…

I live in Belgium, heart of Europe. The intensity of most satellites is strongest in this region, so I don’t worry about reception. (see here for example: _http://www.lyngsat-maps.com/maps/hb6.html). Main satellites I want to watch are Hotbirds (13°) and Astra (19.2°). Follows that I have to motorize the “dish”, as I don’t see any other option.

So, if I don’t have to worry about elevation and skew, I don’t think I have to worry about anything else, right?

Kind regards,
Davor

 

[Robbo]

Yep, once you have set the dish and motor up properly to track the arc, the elevation and skew are taken care of by the motor as it turns. (The axis of rotation is aligned to the earth's polar axis).

you should read Rolfs guide on setting up a motorised dish, the most important thing to do to make things easy, is to get the mounting pole perfectly vertical.

 

[Davor]

Sorry for the links and the double post. Will read the guide

 

[Channel Hopper]

Yep, once you have set the dish and motor up properly to track the arc, the elevation and skew are taken care of by the motor as it turns. (The axis of rotation is aligned to the earth's polar axis).

True for small dishes and footprints destined for your location, but not always the case when looking for other satellites that may be receivable.

Some spot beams are also off 'skewed' by a few degrees as they are steerable from the groundstation.