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VSAT technology and installation >> Dish pointing and alignment >> polar mount main axis angle https://www.satsig.net/cgi-bin/yabb/YaBB.pl?num=1208734859 Message started by voyager1 on Apr 21st, 2008 at 12:40am |
Title: polar mount main axis angle Post by voyager1 on Apr 21st, 2008 at 12:40am
Dear people of the satsig forum.
My name is Sebastian from the Netherlands and this is my polar mount. (original image file https://www.jol-oudieplas.info/polarmount.jpg ) Normally I would ask the dutch sat4all board for help, but it seems all the knowledge is gone. Most people use diseqc motors over here. The big plate on the back is a convertor plate I made. The polar mount is used for a 1.2 echostar dish, but it has a strange problem I think a have the wrong feed arms (to short) so a made this to fit my channelmaster. I believe if done it right, center of the dish is correct. I’am trying to setup a 1.2 channel master offset dish, this is my first polar mount 36v motor setup. I can setup a diseqc motor in a few minutes but this thing I can’t figure out. I have read your “Setting up a polar mount satellite dish - offset feed dish” But Iám afraid it’s over my head and I hope you can help. I need to know my polar mount main axis angle. My declination angle I always figure out by moving the dish up and down, watching the signal and BER levels on a sat receiver. But if you can give me the right angle I will be most pleased ;-) This is my data I have so far : Latitude = 52.6297, Longitude = 4.8560 Lat = 52 degrees, 37.8 minutes North Long = 4 degrees, 51.4 minutes East If you want to point a satellite TV dish at Satellite= 5.1 East orbit longitude Dish elevation= 29.9, Azimuth= 180.9 (magnetic compass), Polarisation= -0.2 We use Sirius at 5 east to find the south its really handy. Your program gives me the following data : Satellite orbit 5.1 Site latitude 526297 Site longitude 4.8560 Dish Azimuth ( true north) 179.69 Dish Azimuth (magnetic north) 180.86 Disk elevation 29.86 Slant range 38626.92 Polarization till -0.19 Polar main axis angel 53.3 Polar mount dish offset till 6.86 Hope you can help me with my angle numbers. Kind Regards Sebastian |
Title: Re: polar mount main axis angle Post by Eric Johnston on Apr 21st, 2008 at 9:35am Main polar axis angle Your main axis angle is about 60 deg. This is too large. Reduce to 53.3 deg. Small downward tilt (declination) angle Achieved by making C larger than A. Measure lengths A and B Assuming the size of the L shaped metal brackets cancels the dish offset angle... I see that A and C are presently the same, so your downward dish tilt is now zero deg. You need to lengthen C or shorten A, so that C is longer than A Note tan(6.86) = 0.12 = opposite/ adjacent C = B* tan (tilt) + A C = B * 0.12 + A Work this out and then adjust distance C. I think you need to do this in two places. Make the same adjustment on each side. Any problems, come back here. Best regards, Eric. |
Title: Re: polar mount main axis angle Post by voyager1 on Apr 22nd, 2008 at 12:35am
The first thing I did was to put a small metal plate on my main axis.
The only thing I could get my hands on was a geo triangle, the metal plate on the back of the geo showed my disk angle. It was something like 57 dec. I changed it back to 53. Then I put the declination angel down till I got the best signal on my digisat pro. I know I have to measured it but I wanted to try it out this way first. The signal on Sirius was about 96% on my signal meter before, but now I only got 70% max. I was confused so I took my topfield 5000 with me on the roof and looked at the Bit Error Rate. And it was good. 100%. I turned the disk manually using a commodore 64 joystick en turned it to Turksat 1c @45 dec E. made a very small adjustment to the declination angle. Turned it to hispasat @ 30 dec w and the quality of the signal was still 100% Still I have the feeling I did something wrong. Did I put the 0 on the geo triangle at the correct location? Why is the Digisat pro signal meter telling me the signal strength is down by 20% All with All, it was a useful day, it a lot better now. Thanks for helping me. |
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