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You often see multi sat LNBs for sale, often for HOTBIRD & ASTRA1. What I can't understand is you are never told what size dish the multi LNB is for. Surely the bigger the dish the greater the seperation of the LNBs?
Am I not understanding something here ?
Any ideas? thank you in advance
Usually these would be used on an 80Cm-1Mtr dish, I certainly have never heard of anyone using them on a larger dish.Quote:
Originally Posted by dave1234
there are different ones with different spacing ie. 4 degrees and 6 degrees, the 6 degree ones being the more available ones.
It all depends on the spacing of the required Sats you would be trying to receive.
regards mobley2
as above , a 6 degree spacing will work on an 80cm or 90 cm or 95 cm or 100 cm or a 110cm dish , but typically its an 80 or 85cm dish
I have a 80 cm dish with 3 LNB'S fitted. I set up on 13e as my primary to align the dish, then i fitted my secondaries 19e and Thor 0.8w all connected to 4 to 1 down switch fitted to the frame of my dish. I scanned each satelite on to my receiver first starting in with position 1 Hotbird 13e, position 2 Astra 19e, position 3 Thor 0.8w, As for my Astra 28e i ran this from my sky mini dish (Sky LNB with 4 connections 2 of which went to HD Skybox for Sky HD, the third connection on the Sky LNB is a spare) the 4th Sky LNB connection is then connected to the 4 position on the down switch and scanned to position 4 on the receiver. By using the Sky dish for 28e this gives room on the 80cm dish to easily fit the 3 LNB'S for 13e, 19e AND 0.8w. Do hope this all make sense
Several months ago I bought a 3 way monoblock with 3 degrees of separation between feed horns, I used it on 13e and 16e and 19e, I lined it up on the weakest one which is 16e and both 13e and 19e came in all right as well on an 80cm.
Out of curiosity I'll try it with a 60cm.
To give Dave1234 an oversimplified explanation, if the larger dish was say a 60cm with bits added on the outside to make it an 80cm you would not expect the spacing to change.
Most of our dishes are just part of a parabola. The offset dish is just the bit above the centreline so that it doesn't look like it is pointing upwards at around 30degrees.
(If one took the shape of a 60cm prime focus dish and kept extending its outer edge it would ultimately give zero extra gain - for that reason the largest practical dimension would be that which terminated prior to, or at the very most, level with the LNB. Then to accomodate larger dish sizes the focal length of the LNB would need to be larger).
Generally, I don't like monoblocs but your case would be the exception. That is because very few individual LNBs can be put closer than 6 degrees. A bodge solution using individual LNBs can sometimes be achieved by mounting the centre one upside down.Quote:
Originally Posted by TonyO
Thanks for the thought provoking responses. The amount of off-set between LNBs is very complicated to work out using pen and pencil because parabolas are complicated.
I am using a 1.2 metre dish in southern spain. The dish is pointed at 28E and gives a good signal. (I am using standard LNBs) I have managed to get 26E strong signal and 19e strong signal when I follow the descending line of the 3 LNBs looking for Hotbird I get nothing at all. I have no idea why this ?? any ideas ?
As the Sats get nearer to your longitude they will be higher in the sky.
Try lowering the LNB quite a bit compared to 19E for 13E OR alternatively raise the dish angle a bit. The skew may also need tweaking.
19E is very strong over most of W. Europe so that is why it didn't take much finding.
I will try that thank you. I think the sat positions should follow a downward sloping curve rather than a straight downward line so interesting idea
As has already been mentioned above, mount the Lnb that you are trying to get13E on ...Below, the arm. A friend of mine had a similar problem
and this was the way he sorted it.
regards mobley2
if you are using more than one lnb the bigger the dish the better the larger the distance between lnbs
these multi lnbs 2 lnbs in 1 are dezined for 80 cm dishes any dish larger they wont work properly because the larger the dish the greater the distance between dish and lnb there for the feed horns need to be father apart me my self I prefer 1 lnb for each satellite
I setup a 120cm dish in southern spain about 7 years ago 28.2, 19 and 13 east. As has been said 19east is an easy catch for 13 east I had to extend the multilnb arm and bend it down it took ages to find it but it worked well untill I installed a motorised dish.