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Pictures of Members' Setups and general satellite
Polar mount stabilisation
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<blockquote data-quote="RimaNTSS" data-source="post: 935828" data-attributes="member: 312276"><p>[USER=329484]@st1[/USER] </p><p></p><p>Thanks for sharing your doubts and all the questions. I wold like to show you one picture. [ATTACH]81265[/ATTACH] Why do you think this construction is stable? And even if we apply some power to one of the forks, whole construction goes to stable position afterwords. Right, that is because Center of Gravity (CG) of construction is below the turning axis. If we turn forks upside-down, CG will move upwards, construction will become unstable and fell down (that what our polar-mounted antennas are basically doing. </p><p>Just imagine that, in our case, turning axis is Polar axis and the construction (forks, cork and match) is our antenna system (dish, feedarms, 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:" />. Perhaps it is not so easy to practically find out where antenna system has CG, but there is some for sure (I marked it as red dot #1). We see that, wherever CG #1 is located it is well above Polar axis, therefore system is unstable.</p><p>In your thoughts you forgot about one very important parameter of the PM system- that is Declination angle, and this angle for my location is almost 8*. On the drawing it is difference between Polar axis angle (blue line) and Declination from horizontal plane (green line). For sure, somewhere those lines will intersect each other. So, if we move antenna along green line, somewhere it's CG will touch blue line and even go under it (red dot #2) [ATTACH]81266[/ATTACH] </p><p>As you rightly pointed out, perhaps it is also good idea to move antenna backwards. Yes, right, that will work, and will work even better (red dot #3)[ATTACH]81267[/ATTACH] . But for this you need more mechanical work to be done. One day I will do that, of course. </p><p>Bigger actuator is not always good solution BTW.</p></blockquote><p></p>
[QUOTE="RimaNTSS, post: 935828, member: 312276"] [USER=329484]@st1[/USER] Thanks for sharing your doubts and all the questions. I wold like to show you one picture. [ATTACH]81265[/ATTACH] Why do you think this construction is stable? And even if we apply some power to one of the forks, whole construction goes to stable position afterwords. Right, that is because Center of Gravity (CG) of construction is below the turning axis. If we turn forks upside-down, CG will move upwards, construction will become unstable and fell down (that what our polar-mounted antennas are basically doing. Just imagine that, in our case, turning axis is Polar axis and the construction (forks, cork and match) is our antenna system (dish, feedarms, LNB). Perhaps it is not so easy to practically find out where antenna system has CG, but there is some for sure (I marked it as red dot #1). We see that, wherever CG #1 is located it is well above Polar axis, therefore system is unstable. In your thoughts you forgot about one very important parameter of the PM system- that is Declination angle, and this angle for my location is almost 8*. On the drawing it is difference between Polar axis angle (blue line) and Declination from horizontal plane (green line). For sure, somewhere those lines will intersect each other. So, if we move antenna along green line, somewhere it's CG will touch blue line and even go under it (red dot #2) [ATTACH]81266[/ATTACH] As you rightly pointed out, perhaps it is also good idea to move antenna backwards. Yes, right, that will work, and will work even better (red dot #3)[ATTACH]81267[/ATTACH] . But for this you need more mechanical work to be done. One day I will do that, of course. Bigger actuator is not always good solution BTW. [/QUOTE]
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