satellite dish install on northfacing wall - dublin

dodzy

Just wondering how low we can install a dish on a NTH facing wall ? I've seen some setups with 80-90cm triax on T&Ks set up on north facing walls. Typically, they look to be just above the gutter line and literally pointing at the ridge tiles. Dont want to mount on sidewall as the apex is obviously more difficult to work on (narrow side entrance and all that)

Dishpointer.com has an obstacle distance v height guide but I know, based on what i've seen , that some dishes can get very close to structures, and still work well.

What angle is the signal transmitted from a satellite to the actual dish ? ( typically astra 28.2 ), or does this information help ?

Currently, I have a standard elliptical type sky dish located on a rear garden wall, 6 ft from ground level and approx 20ft from rear of house. Height to gutter is approx 18ft and then the roof pitches upwards for approx 10ft. I scanned a few transponders no problem on a triax meter i got for messing around with.

I'm sure the professionals can just look and tell the height they need in a given situation ??

Peter Rhea

In Dublin, the elevation angle for Astra 2 is 21.3 degrees, according to dishpointer. There's no way of just looking & knowing if you have enough clearance behind an obstacle.

In your example with the Sky dish on the garden wall, you have to factor in any rise or fall in the ground from the house & also the pitch angle of the roof, which in your case is almost certainly more than 21.3 degrees, unless it's a strangely proportioned house. If the garden is level, you'd need to be over 56 ft. back to clear the 22 ft. above the dish height.

You can work it out with something like this trig. calculator.

watty

A rough test for 28.2E anywhere in Ireland.

Fold a square in half twice is 22.5 degrees. Have one long edge level and point short edge to the South East. If the top slope edge sees sky, then Freesat/Sky will work.

Saorsat is nearly 20 degrees closer to due south and nearly 10 degrees apparently "higher" in the sky as it's at 9E. So less likely to be blocked.

You need a certain degree of clearance (larger as the object near path is further away) due to what is called "Fresnel zone". So "Free path" is actually like a pair of elongated cones back to back, one end at your dish, the other at Satellite's dish and the fattest part in space 1/2 way between.


If the dish bottom edge is about 200mm (8") above the gutter it will clear many roofs

5/12 - still walkable 22.62°

At a Pitch of a bit less than 5/12 (22.6 Degree) the roof can be ANY size.
If the roof is steeper, then the wider the house the higher the dish has to be above the gutter. See
http://www.pole-barn.info/roof-pitch.html

This applies if the roof peak is exactly at right angles to the satellite direction. At ALL other angles of the relative direction of house and satellite you can have a steeper roof (of any size) as the relative angle differs from 90.

SalteeDog

watty wrote: »

You need a certain degree of clearance (larger as the object near path is further away) due to what is called "Fresnel zone". So "Free path" is actually like a pair of elongated cones back to back, one end at your dish, the other at Satellite's dish and the fattest part in space 1/2 way between.

I wasn't aware of that. Are there any calculators available for the radius of the fresnel zone at a certain distance from the dish?

watty

Radio Mobile does it for VHF to UHF to Microwave for terrestrial links. (free download but not a program for beginners, designed for RF network planners)
There certainly are, but I don't know which online ones might exist.

Maybe assume a 2 to 5 Degree wide cone on Ku and maybe 1 to 3 degrees on Ka. Due to elevation it's a much less severe issue than Terrestrial where a hill or building a few km away can degrade UHF TV even though you have LOS of the mast.

I think it's purely linearly related to the wavelength. So LARGE for Band II Radio and small for Satellite.

dodzy

watty wrote: »

A rough test for 28.2E anywhere in Ireland.

Fold a square in half twice is 22.5 degrees. Have one long edge level and point short edge to the South East. If the top slope edge sees sky, then Freesat/Sky will work.

Saorsat is nearly 20 degrees closer to due south and nearly 10 degrees apparently "higher" in the sky as it's at 9E. So less likely to be blocked.

You need a certain degree of clearance (larger as the object near path is further away) due to what is called "Fresnel zone". So "Free path" is actually like a pair of elongated cones back to back, one end at your dish, the other at Satellite's dish and the fattest part in space 1/2 way between.


If the dish bottom edge is about 200mm (8") above the gutter it will clear many roofs


At a Pitch of a bit less than 5/12 (22.6 Degree) the roof can be ANY size.
If the roof is steeper, then the wider the house the higher the dish has to be above the gutter. See
http://www.pole-barn.info/roof-pitch.html

This applies if the roof peak is exactly at right angles to the satellite direction. At ALL other angles of the relative direction of house and satellite you can have a steeper roof (of any size) as the relative angle differs from 90.

Thanks Watty, a mine of information as always. Much appreciated. If I mount the dish in x location, and I receive the first transponder on my list with a relatively good signal / quality level, will i potentially still run into problems with other transponders on the list ? and if so, acquiring the weaker transponders would ensure a better result ?

Peter Rhea

Worth taking a look at this: http://www.wrightsaerials.tv/reference/dish-screened-by-roof.pdf for a graphic explanation & some advice on fixings.

I would think most installers would regard any dish location worked out beforehand as approximate only & would leave some leeway to increase dish height, to see if an improvement can be found once they have the meter connected.

SalteeDog

Advice is normally to align first using the strongest transponder (Channel 5 I think for 28.2) and fine tune using the weakest one (Horror Channel). Given 28.2 is a group of satellites with multiple beams there is a significant difference between weakest and strongest. The strongest transponders are on Astra 1N. Weakest are on Eutelsat 2A.

dodzy

SalteeDog wrote: »

Advice is normally to align first using the strongest transponder (Channel 5 I think for 28.2) and fine tune using the weakest one (Horror Channel). Given 28.2 is a group of satellites with multiple beams there is a significant difference between weakest and strongest. The strongest transponders are on Astra 1N. Weakest are on Eutelsat 2A.

And acquiring knowledge on strongest vs weakest saltee? Is it established from experience or readily available info on t'internet ? Thanks again for the info folks.

Peter Rhea

Astra 1N is certainly the strongest at 28.2 east atm. You shouldn't have any problems with 'weak' tps unless maybe in the western extremes of the country.