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dish pointing prob.

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Sep 18th, 2006 at 8:23am  
Hi Eric,

We do use the Sat master pro software for locating our satellite...now lets assume the follwoing Scenario...

I have a prodelin 2.4 m dish with C band feed , Norstat LNB ,Datum Scpc & Ipricot DVB Reciever..
We are in Abuja - Nigeria and would like to point our Dish to AMC-12. (37.5W)

input info:
9.20N
7.18E
Sat Long: 37.5W
inclination :0
polariztion : 0

the Satellite look angle i got is :
elevation :37.71 degree
true azimuth : 260.82
azimuth compass paring : 262.42
polarization offset: 77.12
path distance to sat: 37958.19


Now, my questions are :

1- is the info entered correct?
2- which  azimuth shouls i take ? the true or the compass bearing?
3-if i want to know the look angle , should i use the (elevation :37.71 degree) got from the masterpro software? or 37.75 - (offset angle) which might be 22.5 degree?
4- someone told me to do it like that :
90 - [ look angle from sat masterpro- offset angle ] is that correct?

5- when i used my SUNNTO ( inclinometer ) for the elevation i was able to get a clear horizon above 37 degree...is that put me on the safe side?

6- what is the frequency i use to track the satellite? i have digital meter , and i thot i might program the frequency and then track the signal ...etc , just the  way we do it with PAS 1R , PAS 10...etc , when i called one of the engineer in the company he said i should look around 1350 MHz , Is that enough?

Thanks allot for your prompt response....



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Eric Johnston
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Reply #1 - Sep 18th, 2006 at 12:47pm  
1- is the info entered correct?  Yes.

2- which  azimuth should i take ? the true or the compass bearing?   

If you have a compass use the compass bearing.  It does not much matter, just swing the beam boldly near the correct angle.  Tonight the sun sets at an azimuth angle of 271 deg (i.e. in the west) , so the satellite azimuth is 10 deg to the left of that.

3-if I want to know the look angle, should I use the (elevation :37.71 degree) got from the masterpro software? or 37.75 - (offset angle) which might be 22.5 degree?

I don't know the offset angle of your dish.  If the offset angle is 22.5 deg then the front face of the dish needs tilting backwards at 37.7 - 22.5 = 15 deg.  There may be a paper in the box with the antenna that tells you about offset angle.

4- someone told me to do it like that :
90 - [ look angle from sat masterpro- offset angle ] is that correct?

Apply a plank of wood across the front of the dish.   Upright is 0 deg slope.  Tilted backwards 15 deg may be what is wanted.   You may well have to add/subract 90 deg or read the scale backwards.  You can apply the inclinometer either way round and also tipped 90 deg so as to get readings that make sense.

Prodelin dishes may have a piece of metal lower down behind the dish which is at right angles to the beam.  You can place the inclinometer here.

5- when i used my SUNNTO ( inclinometer ) for the elevation i was able to get a clear horizon above 37 degree...is that put me on the safe side? 

I am worried what you mean.  It is best if the horizon is some 5 or 10 deg below the satellite (i.e. clear above 32 or 27 deg elevation).   Get someone to aim a plank of wood or pipe in the required direction and apply the inclinometer to the wood/pipe.   If there is a mountain horizon or building wall exactly at an elevation angle of 37 deg then the satellite is hardly visible.  You are welcome to try and see if it is possible, but it may not work and you may have to move the dish to a better location. 

6- what is the frequency i use to track the satellite? i have digital meter , and i thot i might program the frequency and then track the signal ...etc , just the  way we do it with PAS 1R , PAS 10...etc , when i called one of the engineer in the company he said i should look around 1350 MHz , Is that enough?

What carrier are you trying to receive ?  See http://www.lyngsat.com/amc12.html
There is a Metro Ghana carrier at 3805 MHz so that might be detectable at 5150 - 3805 = 1345 MHz ?
This assumes your LNB has a 5150 MHz LO frequency.  It is a very small carrier: symbol rate 2142K 7/8 FEC.

Please note that AMC-12 uses linear polarisation for C band, so polarisation angle adjustment is important. For Horizontal receive polarisation the starting position is with the LNB waveguide with its broad faces to either side and the thin edges at top and bottom.  Then rotate adjust the LNB/Feed by facing towards the satellite and turning it clockwise 77 deg.   This is a very large movement.  Placing an inclinometer sideways across on the LNB will help a lot.

Best regards, Eric.
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Reply #2 - Sep 18th, 2006 at 11:12pm  
Hi Eric,

Thanks for your reply...hmmmm , i think i am having a serious problem of relocation the dish...waw!!
Anyway, when i stood by the dish and used my inclinometer (SUUNTO)  it gave me a clear horizon on 35 degree ( elevation ) and (260 degree horizion which i think i can rotate it to 250-270 degree )!!
According to your explanation , it means i have to get a clear horizon (elevation ) on  37.7 [ satmaster pro ] -  22.5 degree [prodelin  2.4 m Rx/Tx Antenna PN 1251 N
  Standard C band, Xpol linear feed ] ...

which is : about 15 degree (elevation view)... i think i have to relocate the dish...No Magic Eric ?! hhhh! again to remove the kingpost mount...etc!!

Anyway, thanks allot ...i think it was great answer that i wont forget again..

Also i thank you for the Gana beam you mentioned...you are right the LNB LO is 5150 C band , and i have already removed the Circular polarizer ...etc

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Eric Johnston
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Reply #3 - Sep 19th, 2006 at 8:21am  
The 22.5 deg offset (or whatever the offset angle actually is ) is irrelevent to whether or not you can see the satellite.

The elevation angle of the satellite must be higher then the elevation angle of the horizon, preferably by 5 deg or more.

It sounds as though you have a horizon at 35 deg and satellite at 37.7 deg.  In which case you will still be able to operate but with slightly reduced receive quality due to noise from the ground.

If the horizon is nearby (wall, building etc) then raising the dish a few feet will help.   If it is far away (hills) don't worry.   If it is nearby, be concerned about trees growing, new buildings, safety of people standing or working on nearby roofs.  If the horizon is nearby measure its elevation as seen from just under the bottom edge of the dish.

Test with the existing location before considering moving the dish.

See here on how to use a compass

Best regards, Eric.
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« Last Edit: Oct 14th, 2007 at 5:02pm by Admin1 »  
 
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