thanks all,
my mast is perfectly plumb from every angle...
I appreciate the insights, but if I were as far off as you suggest why would I be tracking from 60 to 100 just fine and then lose everything after that?
I have line of sight to the far western sats, the fact that I can hit 119 with the "pzza dish" is testament to this.
I'm certain I've optimised my signal, and that this dish needs no further alignment.
could there be something wrong with my motor? I did notice a bit of play in it, but assumed this is normal.
Quasimodem,
As always, the mast must be absolutely plumb and there is no allowance for skimping here. You state that your mast is plumb and I trust you on this, but this is one of those bold print disclaimers that I always try to toss out there everytime, just in case some other person is listening in and the plumb of the mast proves to be the source of their errors.
Now, here is the dilemna with making a motor and dish track the arc properly. We are dealing with the latitude angle of the motor and the elevation angle of the dish bracket, not to mention the azimuth angle (E-W aiming) of the entire assembly.
If these angles are not all precisely correct, but you are semi-close, you may track only a portion of the arc. The portion of the arc where your system is tracking good may be on the east side, in the center or on the west side of the arc or any other portion of it.
Let's say that you are tracking the arc well near the center of the arc, which is often the case. The further west or east you drive the motor, the track of the motor and dish may be falling low and away from the real arc. In the center of the arc, you may be high, but not too high so that you lose the signal.
Refer to the diagrams I attached, if the picture isn't too clear, try the zip file (it's the same thing, but might look more presentable than the image I have attached). These diagrams are for polar mount dishes, not offset ones like you are setting up now, but you can apply it just the same. Just consider your motor latitude angle as the declination angle.
Going back and starting at the beginning:
1] The mast must be plumb.
2] The motor latitude must be set precisely to your site's latitude coordinate.
3] The motor tube must have no slop or play on the motor stem and the internal gear backlash must be set correctly. This cannot be too tight or you motor will move too slowly or fault out and may draw excessive current from your receiver. Or it may stop short of the target position. It cannot be too loose or the dish assembly will "flop" in the wind and even on a calm day, the dish assembly will not stop at the same positon each time... It may sag one direction or the other depending upon how gravity pulls upon it.
4] The motor assembly must be aimed directly at your true south satellite. This satellite's orbital position (degree) would be the very nearest number to your site's longitude degree. i.e. if your latitude is 96.4W, then you must use the satellite at 97.0W as your true south sat. You won't be able to accurately pinpoint this angle without the response from the signal meter on your receiver or a very good meter, so at first you will be merely roughing it in.
5] You should peak first on your true south satellite, then work your way east and west of that sat (center sat) and tweak your dish elevation and your entire asemblies azimuth angles to peak the signal. DON'T MOVE THE MOTOR LATITUDE unless you suspect it to be inaccurate.
6] If you suspect that you haven't dialed your motor latitude correctly, then remove the dish from the motor tube and (with your motor driven to the zero degree position) place a very good quality dial inlimeter on the bottom side of the motor housing or the belly of the motor and adjust your motor latitude so that the inclinometer reads an angle equal to: 90 degrees minus your site's latitude. This resultant value would actually be your motor's ELEVATION reading.
LATITUDE + ELEVATION = 90
7] If you are with me so far, then the next step is to confirm the tracking of your arc. go east/west of your true south satellite as far as you are able without losing the signal from the satellites. If you begin to lose the signal, go back a small degree towards your true south sat and gently grasp the dish from behind and put a very slight pressure to try to tilt it upwards or downwards and record which direction you need to move the dish elevation to improve the signal. Don't move anything yet...
8] Next, do the very same thing as in step 7, but try to turn the dish very slightly east or west and see which direction improves the signal. Take this informatin and that gathered in step 7 and try to adjust your dish just a ery minor amount in the direction/s necessary.
9] If you are highly satisfied with your reception from the true south satellite, then use USALS for all your motor controlling and poitioning. Don't try to use DiSEqC 1.2 as that will hide your dish and motor alignment errors and you won't be able to detect which direction you truly need to move to peak the signal. Using USALS will automatically drive the dish to that position and then you can test/check the alignment for errors.
10] The rest is all an affair of redundantly retesting and re-tweaking your alignments.
This process requires much patience as I have often stated, but it is just something that needs to be done if you want it right. It isn't easy at first, but you develop a sense for it eventually.
I hope these guidelines will help you and I wish you good luck!
RADAR
