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Thread: Focal point

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    Default Focal point

    Just checked my 2.3m Mesh dish and found it to be 2272MM not 2300MM. Now a run a string over from one end to the other and measures the center of the sting to the base of the dish and got 346MM and used this site to calculate the Focal point and when i calculate the distance for the focal point I found my dish to be 22 mm less focal point. (Focal point is 932MM). Tell me does this cause lower performance "eg" less gain and if so what gain in db would I have lost (having a good guess)
    Last edited by Mr 672A; 06-06-22 at 12:08 PM.



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    Quote Originally Posted by 5GRUBBISH View Post
    Just checked my 2.3m Mesh dish and found it to be 2272MM not 2300MM. Now a run a string over from one end to the other and measures the center of the sting to the base of the dish and got 346MM and used this site to calculate the Focal point and when i calculate the distance for the focal point I found my dish to be 22 mm less focal point. (Focal point is 932MM). Tell me does this cause lower performance "eg" less gain and if so what gain in db would I have lost (having a good guess)
    2.3m more like a marketing jargon, Most Chinese made dishes use a US design around 7.5' = 228.6mm but for the metric audience they call it 2.3m.

    Y = 2272 : 2 = 1136² = 1290496 : 346 = 3729.7 : 4 = 932mm is correct.. The dish is basically an optical lense. If the focal point is out by 22mm they would be significant lose... The Focal distance 932mm should be measured from the center of the dish to within 10 to 15mm inside the LNB throat...For the final adjustment use a satellite meter for best BER MER, and optimized polarization, the V and H orientation.
    Last edited by B52; 06-06-22 at 10:14 PM.

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    Quote Originally Posted by B52 View Post
    2.3m more like a marketing jargon, Most Chinese made dishes use a US design around 7.5' = 228.6mm but for the metric audience they call it 2.3m.

    Y = 2272 : 2 = 1136² = 1290496 : 346 = 3729.7 : 4 = 932mm is correct.. The dish is basically an optical lense. If the focal point is out by 22mm they would be significant lose... The Focal distance 932mm should be measured from the center of the dish to within 10 to 15mm inside the LNB throat...For the final adjustment use a satellite meter for best BER MER, and optimized polarization, the V and H orientation.
    So to be clear the Focal distance 932mm should be measured from the center of the dish that has a 3MM steel plate on top of the mesh and allow 10 to 15mm inside the LNB throat so the TIP of the LNB where the plastic wasp cover lives it should be 932 - 10 mm (inside the Throat of the LNB) = 922 Focal point ( I will make a 16MM Stick to measure that @ 922MM) and use use my satellite meter for best BER MER.

    Funny thing is the 3MM steel plate in the middle, you will think that will upset the measurement a little because the plate is 3mm above the mesh.

    thanks.

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    What bothers me is the 4 struts are FULLY OUT and yet I have 22 MM short when its fully extended. Possible wrong arms for the Dish. The Only thing I can do is drill new holes on the struts where the end are that goes on the dish and I can pick up 9MM and file the end where the slot is on the Feed horn end that will give me another 5 or 6MM (leave 1MM) . I want to use the two bolts on each arm on the feed horn end as i dont like to uses only one bolt for each strut to extend it out further
    Last edited by Mr 672A; 08-06-22 at 12:01 PM.

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