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Fringe Reception General
Coupling two 1.80m dishes as one 3.60m dish
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<blockquote data-quote="ouagadougou" data-source="post: 112073" data-attributes="member: 187470"><p>Hi all, </p><p></p><p>I recently found this forum so hello everyone. I noticed that you have quite a few threads running that are of a detailed technical nature <img src="https://www.satellites.co.uk/styles/default/xenforo/smilies/smile.png" class="smilie" loading="lazy" alt=":)" title="Smile :)" data-shortname=":)" /> and a few things occurred to me regarding this thread in particular.</p><p></p><p>RF Combining (Pre LN<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite6" alt=":cool:" title="Cool :cool:" loading="lazy" data-shortname=":cool:" /> - you are likely to achieve less than 2.8dB of extra gain from RF Combining 2 dishes of the same size due to the overall collecting area of the 2 dishes and the added losses of the combining network waveguides, connectors and combiners. It would be better to just have 1 new reflector with the same area as the 2 proposed dishes combined, this should give an extra 3dB. <strong>Does anyone have any practical results from RF combining 2 dishes ??</strong></p><p></p><p>IF Combining (Post LN<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite6" alt=":cool:" title="Cool :cool:" loading="lazy" data-shortname=":cool:" /> - this gets quite difficult and requires each lnb to be phase locked to the same frequency plus delays between the 2 IF paths have to be compensated. Exactly how much gain you would get in a system working in real time is very debateable and is unlikely to be better than the 3dB mentioned above unless you can apply some mathematical manipulation of the IF signals. <strong>Does anyone have any practical experience of IF combining ??</strong></p><p></p><p>Interferometry - not sure this will work either as it relies on the earths motion to some extent to allow aperture synthesis when observing a distant source and we wouldnt have this relevant motion when observing an earth satellite as its motion is limited by its position in the Clarke Belt. Real Time Correlation could also be an issue. <strong>Does anyone have any practical experience of Realtime Correlation of broadcast type signals or the use of Interferometry for near earth orbiting objects like a satellite ??</strong></p><p></p><p>Diversity combining - digital microwave links use 2 antennas with diversity switching but the diversity switch selects the best of 2 signals from 2 antennas and doesnt actually do any adding or actual combining of the 2 signals in real time.</p><p></p><p>Just a few ideas and questions. Personally I am considering building a 4m offset reflector for simultaneous use on multiple frequency bands (Ku/C/Amatuer) as a test case before looking at a final dish size of 6 to 8m homemade. I have 5 surplus 2m Prime Focus Dishes at the moment which would make a great array if I was convinced that combining them would be worth it !! <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite53" alt=":confused" title="Confused :confused" loading="lazy" data-shortname=":confused" /> .</p><p></p><p>Cool forum guys.</p><p></p><p>Cheers.</p></blockquote><p></p>
[QUOTE="ouagadougou, post: 112073, member: 187470"] Hi all, I recently found this forum so hello everyone. I noticed that you have quite a few threads running that are of a detailed technical nature :) and a few things occurred to me regarding this thread in particular. RF Combining (Pre LNB) - you are likely to achieve less than 2.8dB of extra gain from RF Combining 2 dishes of the same size due to the overall collecting area of the 2 dishes and the added losses of the combining network waveguides, connectors and combiners. It would be better to just have 1 new reflector with the same area as the 2 proposed dishes combined, this should give an extra 3dB. [b]Does anyone have any practical results from RF combining 2 dishes ??[/b] IF Combining (Post LNB) - this gets quite difficult and requires each lnb to be phase locked to the same frequency plus delays between the 2 IF paths have to be compensated. Exactly how much gain you would get in a system working in real time is very debateable and is unlikely to be better than the 3dB mentioned above unless you can apply some mathematical manipulation of the IF signals. [b]Does anyone have any practical experience of IF combining ??[/b] Interferometry - not sure this will work either as it relies on the earths motion to some extent to allow aperture synthesis when observing a distant source and we wouldnt have this relevant motion when observing an earth satellite as its motion is limited by its position in the Clarke Belt. Real Time Correlation could also be an issue. [b]Does anyone have any practical experience of Realtime Correlation of broadcast type signals or the use of Interferometry for near earth orbiting objects like a satellite ??[/b] Diversity combining - digital microwave links use 2 antennas with diversity switching but the diversity switch selects the best of 2 signals from 2 antennas and doesnt actually do any adding or actual combining of the 2 signals in real time. Just a few ideas and questions. Personally I am considering building a 4m offset reflector for simultaneous use on multiple frequency bands (Ku/C/Amatuer) as a test case before looking at a final dish size of 6 to 8m homemade. I have 5 surplus 2m Prime Focus Dishes at the moment which would make a great array if I was convinced that combining them would be worth it !! :confused: . Cool forum guys. Cheers. [/QUOTE]
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Fringe Reception General
Coupling two 1.80m dishes as one 3.60m dish
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