g8vkv Posted May 31, 2009 Share Posted May 31, 2009 Hi,We have 2 dishes on the house - a 60cm and an 80cm.About 12 months ago, I set the 60cm dish (because it's easier to get hold of) to point at Astra 2 for Freesat - it works OK, but the signal tends to break up in rain and in the summer (ionisation?). So, I decided to bring down the bigger, 80cm, dish and use this - hoping for an improvement.Now, both dishes are marked with a scale for elevation.My understanding of elevation in this context is that it's the angle between horizontal and the direction the dish points - so the more the dish is tilted upwards, the bigger this angle should become. The scale on the 60cm dish follows this logic - the angle increases as you point higher into the sky. However, the scale on the other dish (80cm) has the opposite sense - the higher you point, the lower the angle gets.So basically I'm confused.[blink] Link to comment Share on other sites More sharing options...
Martin963 Posted May 31, 2009 Share Posted May 31, 2009 I think my maths teacher at school would have called them complementary (as opposed to supplementary) angles.I'm guessing that the scales are the same apart from the (rather fundamental) fact that one scale is (90 - x) when the other is just plain x.But does it matter much? I've never use the scale on a dish for set up, I don't really think they have any great accuracy, and depend on the support arm being dead on vertical.So I'd use the signal meters on the box and peak up the performance like that. Link to comment Share on other sites More sharing options...
Anton Redman Posted May 31, 2009 Share Posted May 31, 2009 "My understanding of elevation in this context is that it's the angle between horizontal and the direction the dish points" . Not quite so easy. The LNB arm is almost always off set from the centre of the dish typically on a 80 cm dish by 22.5 degrees so if you want 30 degrees the dish is only 7.5 degrees from horizontal. I have made up a large protractor with a plumb line which clamps to the arm because short of shimming the bolts which attach the dishes to our house you cannot get the pole exactly vertical. In any event as Martin's posting above you can use the scale to find the Satellite cluster but you need to fine adjust with the signal strength meter of the receiver. On other thought the clamps are frequenly common to at least two sizes of dish which uses different offsets for the LNB arm and hence different scales sometimes with the arm inverted Link to comment Share on other sites More sharing options...
g8vkv Posted June 2, 2009 Author Share Posted June 2, 2009 Thanks for taking an interest.I finally managed to get a signal (dish clamped to workmate) and was amazed by how sensitive the alignment is. Just a twitch will send the signal from excellent to non-existent.As a matter of interest, the plane of the dish is about 10 degrees off vertical for the best signal/quality.After I've fine-tuned the elevation & LNB twist - off onto the roof! Link to comment Share on other sites More sharing options...
Martin963 Posted June 2, 2009 Share Posted June 2, 2009 Well done!As Anton has often so sagely observed, the bigger the dish the more critical the alignment. I've had no trouble up to 1 m, but I believe that say a 1.5 m dish (as required for the BBC in Spain for example) is a real pain to set up.....Glad you're making progress. Link to comment Share on other sites More sharing options...
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