BATC Forum

Oscar 100 dish. X meters diameter, looking at the satellite. How do I calculate if a structure such as a bungalow or workshop roof of height Y will degrade the signal? I am thinking in terms of how far away from the structure must a given diameter dish be for the structure to have negligible effect on the received or transmitted signal? I Googled but haven't found how to calculate this. Thanks. (I picked up a big Andrew dish from Northamptonshire today and want to see where it might go).

Google should have yielded an answer.

You need Fresnel clearance but to a first approximation just make sure there is clearance from the base of the dish to the obstacle taking account of the elevation angle. Just do some simple trigonometry, h = d x tan(elevation). Typically in Southern UK it's going to mean the height of the building has to be quite a bit less than half the distance assuming the dish is on the ground.

You can also use the sun transit which happens twice a year if the sky is clear. The transit happens when the sun appears to pass directly behind the satellite - i.e. sun, satellite and dish are all aligned.


Mike

Edit - size of dish doesn't really matter, you don't want anything in the way. Just think of it like a searchlight. A laser level is a useful tool if you have one. My method involved a step ladder of known height a tape measure and sighting the local tree from about 1ft off the ground.

Ok, thanks very much Mike, I may invest in a laser pointer, I assume mounted 90 degrees to the perpherary of the dish, top bottom and sides, it should ideally not shine on any local objects?

Not quite. Pointing towards the satellite from the edges of the dish. That's not 90 degrees.

Basil wrote: ↑

Sun Sep 12, 2021 8:43 pm

Oscar 100 dish. X meters diameter, looking at the satellite. How do I calculate if a structure such as a bungalow or workshop roof of height Y will degrade the signal? I am thinking in terms of how far away from the structure must a given diameter dish be for the structure to have negligible effect on the received or transmitted signal? I Googled but haven't found how to calculate this. Thanks. (I picked up a big Andrew dish from Northamptonshire today and want to see where it might go).

Hi Basil,
If you are in the UK the satellite is roughly 26° up. ( If your in middle England) Get a stick , point it up towards the satellite (a bit east of south) at 26°. Look up the length of the stick like a rifle. Thats where the satellite is.
Or, download an Inclinometer app onto your phone. use that to find the angle.
You can get a chair or something outside. Prop a sweeping brush against it pointing UP towards the satellite. Put your phone on the brush handle to check the ANGLE its pointing up at and adjust the tilt until you get 26°. Look up the HANDLE to see if it clears any buildings.
NOTE: Your dish won't point up at that angle IF ... its an offset type.
Look at SKY dishes near to you. They are "roughly" pointing the right way. However they "appear" to point much lower towards the horizon. Thats because theyre mostly off-set types where the signal bounces off the dish at an angle & is reflected into the LNB.

Use this website .. move pointer to your location. The angles etc are then displayed on the left of the page.
https://eshail.batc.org.uk/point/

Good luck , have fun

Ken

https://www.dishpointer.com/

is handy, as it has a draggable marker that shows how high off the ground the line of sight is, at any distance from the dish. Typically, the original rotatable dish to the right is partially obstructed to QO-100.

Brian
.

Thanks Brian, that's a handy app. And thanks for all the other replies, I am going to try a laser pointer on the rim of a temporary installation of the bigger dish, just to be sure I am not wasting signal due to a less than optimal location. It's all a bit tight, balancing feed line length, view of Oscar 100 and keeping 'er indoors semi happy! I am also striving to have it in invisible to neighbours and passers by.

And don't forget in 3 weeks time you can visually check you have a clear path - if the sun is shining!

viewtopic.php?f=101&t=7211

73
Noel