My longitude is 121.77 and my true south is 165 since I am

stockgurubear · #1 (**permalink**) 08-04-2005, 06:54 PM

in California, why would my closest satellite be Echostar 121W? and not something near 165? I can't figure it out. Having a hard time aiming the satellite so that it picks up each satellite while the motor is moving it using USALS. Can someone give me a quick explanation? What does True south and my longitude position have in common? Thanks in advance

Admin · #2 (**permalink**) 08-04-2005, 09:03 PM

The satellite closest in Longitude to your locations Longitude is your most True South Satellite.

stockgurubear · #3 (**permalink**) 08-05-2005, 09:15 AM

Thanks for the reply. I am at the antenna set up screen and I let the USALS move the motor. It doesn't seem to pick up anything properly when it stops. I have to turn USALS off as soon as I see green in the quality meter. Do I tigten up all the bolts and the dish when it is peaked at the true south satellite? I can't figure this part out. All the elevation, declination angle, etc seem to be set up properly. I mean if I am at 121.7W and the satellite I should peak is at 121W. That means The motor needs to move the dish .7 from my true south position and lock onto the satellite. Is this a correct assumption?

pmb1010 · #4 (**permalink**) 08-05-2005, 12:04 PM

It is correct, dish only moves .7 from magnetically corrected south setting.

Your dish should not be moving all over the place if you use USALS and move to 121W. (It might try to adjust itself by moving all the way to the limits on one side, then back to 121 to figure out where it is though).

But it should not move a bunch off of your aimed true south when it finally arrives back there.

And you should disregard any of the green blips while it's getting there.

Once on your South Sat, you should scan a transponder to make sure you're on the correct satellite by verifying with http://www.lyngsat.com for the channel/transponder. There's only 1 channel in the clear.
THen tighten up the bolts...

Then use USALS to drive to another sat to see how well it's tracking.

wejones · #5 (**permalink**) 08-05-2005, 01:58 PM

Quote:

Originally Posted by pmb1010

It is correct, dish only moves .7 from magnetically corrected south setting.
...

I know this doesn't change the conclusion, but the above is only true if you are at the center of the earth. Ie the 0.7 deg is measured from the center of the earth, but the angle your dish moves is measured from the surface of the earth, so the angle will be slightly more, since you are closer. Approximately 15% more, depending on your latitude, or approximately 0.8 deg in this case.
I know...... big deal...... but just trying to be exact here. :-)

pmb1010 · #6 (**permalink**) 08-05-2005, 03:32 PM

I was trying to simplify things for the guy.

Bottom line - dish is only going to move only slightly from highest point on arc, to highest satellite on the arc, in most cases.

I was only repeating his number. I did not check for accuracy. It might be .8023421342093420130935234 for all that matter...
#-o

wejones · #7 (**permalink**) 08-05-2005, 06:27 PM

I understand. Essentially no difference with his example.
Besides my failed attempt at humor, I just didn't want him to think you could always just subtract the longitudes. For example, he might think that he could see Telstar-11(37.5) because it's longitude is 84 degrees less than his, whereas it would actually be below his horizon. Ie the error gets bigger as the difference in longitude between him and the sat increases, about a 10 degree difference at the extremes.

stockgurubear · #8 (**permalink**) 08-07-2005, 11:35 AM

Thanks guys for all your wisdom. Still trying to get the best signal. Something could be wrong with the mast not being perfectly plumb, which is what is throwing it off. Will let you know. Anyone from San Franicisco area know what the most East and most West satellite that we can get is?

stockgurubear · #9 (**permalink**) 08-07-2005, 12:23 PM

Can anyone confirm if this satcalc program works? Tell you where you should point the dish for various satellites.

http://www.nerosoft.com/SatCalcView.asp

wejones · #10 (**permalink**) 08-07-2005, 03:07 PM

Quote:

Originally Posted by stockgurubear

Can anyone confirm if this satcalc program works? Tell you where you should point the dish for various satellites.

http://www.nerosoft.com/SatCalcView.asp

It seemed to work OK on a couple examples I tried, however of it doesn't seem to be very up to date with respect to which sats are in it's list, as about 5 of the first 7 things I tried to calculate, it didn't have, like AMC11, AMC10, Galaxy 12, Galaxy 13, Echo 9 and a few others .
Also, be aware that this calculates true azimuth, not magnetic like you would see on a compass.
Also this is an azim/elev calculator, while motorized dishes have polar mounts, so it isn't real useful for aiming except on your true south sat.
Also, realize that when it talks about the angle you should "elevate" your dish, this is referring to the actual aim of your dish, which isn't easy to visualize with an offset dish, although if your dish is mounted on a plumb pole, instead of on a motor, it should be 90- the latitude marking on the dish mount.
But yes, the url does seem pretty close in it's calculation.

EDIT: If you want a program to run on your computer instead, you might try :
http://www.megalink.net/~wejones/tvcalc2k.zip

This is a program I wrote. It is not pretty, but it does a lot of different things related to TVRO dishes, like Azim/Elev , declination, equator crossing times for inclined sats, position of sun and moon, gain calculator for dishes, sidereal time calculator, tabular and real time tracking of LEO sats, and a few other things..