prodelin satellite dish alignment woes

[richardsth]

hi all,

I'm trying to setup a dish and I'm almost there but I have one issue which has got me flumuxed. I've aligned my 1.8 prodelin at Thor and with a meter signal strength is at full strength and bang on 1 degree, but when I aim it at Hispasat I have to adjust the dish up slightly and when I try for the Astra satellites, I have to adjust it back down a little. The Azimouth settings are spot on as these have been checked against an attached scale protractor scale, so is it the dish elevation that needs adjusting or the declination ?

cheers,

Rik

 

[Robbo]

The declination is the dish elevation effectively.

The elevation setting is the bit that enables you to get the axis of rotation aligned with the earth's polar axis

The declination setting, is where you tilt the dish itself up/down.

You have one of two problems, you arc is either 'wonky' or offset to one side.

Make sure your pole is plumb.

Also when the polar mount is at the top of the arc, the dish must face exaclty at due south. Yours it twisted westward a little, hence dropping it down a bit.(assuming that the pole is plumb).

I would use a digital angle guage to get the elevation correct.

 

[Burnham Beech]

Halstead is located at 0.6east so if you aligned on 0.8/1.0 west you will be about 1½ degrees out. Not important with smaller dishes but best to get this right with a 1.8m dish.

I note you say "bang on 1 degree" but you don't say what you mean by this.

 

[richardsth]

Hmm, that makes sense. I'll check the plumbnest of the pole first. For the record, it's the declination that I've been playing with.

 

[Robbo]

Thing is, fiddling with the declination, will never correct the problem, as your arc is not symmetrical. If it was too low on both sides, then it would, but the elevation would also need adjusting as well, the two complement eachother.

 

[richardsth]

So to get the arch symetrical, where would Thor be in relation to it? Right now I've set it to be slightly off centre, should it be dead centre ?

 

[Topper]

According to Google Earth Halstead in Essex is 0 deg 38 minutes East. That means your top of the arc or due south satellite should be there and your nearest satellite is Thor at 0.8 deg West so it is approx 1 degree off your due south.

 

[Robbo]

Thinking about it, it's most likely the pole isn't quite plumb, Though the whole thing might be shifted round slightly eastward too. When aligning to thor, the mount should be at approx 1.4 degrees west of centre. Thus when at centre the dish will point at true south.

 

[Huevos]

I don't know what you are talking about "protractor scale" but once you get close you want to forget any markings and go on performance.

If you are high on East satellites and low on West satellites your whole assembly (dish and polar mount) needs to be swivelled round the mast to the West (clockwise looking from the top of the mast).

If you are low on East satellites and high on West satellites your whole assembly (dish and polar mount) needs to be swivelled round the mast to the East.

If you perfect on your southern satellite but low at both ends of the arc you have too much declination, i.e. your dish is pointing down too much and you have had to put too much polar mount elevation to compensate.

On the other hand if you are perfect in the centre of the arc and high at the ends you have too little declination.

 

[zorbua]

I would say if your pole is plumb, dish facing true south, elevation primed on Thor, then your problem is solved by moving your whole assb (Polar mount+Dish) slightly to the West. Always mark on your pole where you are before making any adjustments. N.B. Must Emphasise that movements should be very slight and check again on the Hispasat and Astra Sats whether there is further adjusting to be done simply by pulling upwards/downwards on the Dish to see if Signal increases or decreases and then moving Assb again further West or East accordingly. Must stress the importance of movements being ever so slight and unlocking of nuts to be sufficient just to move whole assb.

 

[Channel Hopper]

Where would you get a Prodelin 1.8m with polarmount though ?

It's a rare beast

 

[richardsth]

Where would you get a Prodelin 1.8m with polarmount though ?

It's a rare beast

Not really, I told them (******) what I wanted to and they supplied a new Polar mount for it. Mind you, I did have to wait about six weeks for the dish and mount to turn up from the States. Point to remember though, don't get the prodelin actuator to go with it as it costs as much as the dish !

 

[richardsth]

I don't know what you are talking about "protractor scale" but once you get close you want to forget any markings and go on performance.

So that I could gauge where the satellites were, I fitted the scale from a protractor to the back of the mount. So that 0 degrees lined up with the centre line of the mount. It's a simple mod but was an excellent aid to get my bearings. Thor is slightly off centre, while Hispsat is bang on 30 and Astra at 28. Thinking about it now, the whole assembly probably needs shift round slightly as the pole is quite straight. Well if you call 88-89 degrees straight !

 

[sonnetpete]

Well if you call 88-89 degrees straight !

No actually, I wouldn't call that straight! With a dish of that size over a degree out of plumb is a significant error. My pole was out by less than that when I put up my 1M Gibi and adjusting it to within .1° of 90° made a definite improvement. I'd get your pole dead plumb before trying to adjust anything else.

 

[Robbo]

Well if you call 88-89 degrees straight !

Wonky as hell!

 

[richardsth]

Wonky as hell!

Point taken, the pole was straight until I stuck this monster on top of it. I'll get to work on the post, then start with the alignment again; Lordy !

 

[PaulR]

If it moved when you put the dish on then surely this means that either your mounting for the pole isn't sufficient or the pole itself isn't up to the job?

 

[richardsth]

What an insightful lot you are here ! The pole that it's sitting on was designed for a lightweight aluminium 1.5 IRTE Prime focus, but when I went for this monster, I assumed that it would easily sit in it's place even though the post diameter was the same. How wrong I was! Comparing it to the Prodelin groundstand it's it's baby brother. I'll see about getting a longer pole and sinking it in to the concrete before I attack the alignment.

 

[Robbo]

Good luck!

That's the trouble with the larger than average dish, very narrow beamwidth.

 

[Huevos]

Comparing it to the Prodelin groundstand it's it's baby brother. I'll see about getting a longer pole and sinking it in to the concrete before I attack the alignment.

What is the diameter of the pole? I would say 100mm minimum for that dish. And forget sinking the pole in concrete, you want it adjustable.