Usals problem & alignment

[Trust]

Interesting. This is something I want to try have a go at. Is there some calculation I have to do for latitude and Dish Elevation? All the values inverted?

For what reason ? the center of the dish will be approx the same if you put it upside down .
If you want to put the dish more higher , you better drill four new holes and attach the elevation clamp more lower at the dish .
But in that way the rotor has to work harder bringing back the dish from far east or west positions , so a longer pole will be the better way .
The windload at the pole will be the same when the dish is at a longer pole or when you move that elevation clamp .

 

[Channel Hopper]

For what reason ? the center of the dish will be approx the same if you put it upside down .

View attachment 129044

Oh no it isn't.

 

[a33]

Oh no it isn't.

Well, it's time to show us how you think the upside down dish would be higher up, then (e.g. draw it in the picture from Red alert).

I'm with Trust, for the time being (as I was, here: Televes or fracarro? - SatsUK )

Greetz,
A33

 

[TJExcalibur]

For what reason ? the center of the dish will be approx the same if you put it upside down .
If you want to put the dish more higher , you better drill four new holes and attach the elevation clamp more lower at the dish .
But in that way the rotor has to work harder bringing back the dish from far east or west positions , so a longer pole will be the better way .
The windload at the pole will be the same when the dish is at a longer pole or when you move that elevation clamp .

View attachment 129044

if the dish is upside down with the lnb arm at the top it gives a different angle to receive the satellites. Only a guess because I haven't a clue.

 

[Trust]

Made a quick setup in the shed , not with a Gibertini but a Triax TDS 64

 

[Channel Hopper]

I have two systems running inverted dishes out there, where the reasonng was to keep a lower profile of the system from neighbours noticing they had a second dish behind a parapet. Whilst there was of course less of the dish on display, the clamping point was installed substantially lower on the pole as an added bonus, with the same degree of clearance from obstruction.

I'll prove you wrong with the Gibertini 1m I have here, hopefully tomorrow if the rain holds off. It could be the design of elevation mount shifts the reflector further forward than the Triax of course, but the theory remains valid.

 

[Channel Hopper]

Ha, I was right.

Pictures later this afternoon (it started raining a few minutes back) but the important parameter is not the elevation of the satellite, but the of the reflecting part of the dish that can clear any obstacle in between.

I have installed the Gibertini here, an old design of 1m, the elevation bracket design does not allow inversion, since the bolt grooves on the lower locking bolt allow about 40 degrees of movement, not the 55 that would normally be required to reverse it on the pole. If the mechanism had been offset by about 20 degrees from dead vertical then it might be feasible.

I have therefore propped the dish into the position to allow inverted reception, just clearing a shed opposite in the direction of Hotbird, and the measured difference in height to ensure the same signal is a little over 15.5 cms , or 6 inches in old money.

I made an error in the first measurement by taking the lowest height at the top of the boom arm as well, the effective reflector surface is a good 2cms higher than this , though a little further forward, so I believe it can be dismissed.

 

[Channel Hopper]

Pictures, satellite reception was Astra 4A, though I believe whatever bird is chosen it should make no difference, only the clearance at the base of the reflector.

Since I don't have a schematic of the dish here, I will use a Prodelin design in some drawings later to give an idea of what it looks like on paper.

The offset angle is slightly different (17.3 as opposed to 21 degrees) . but the principle is the same.

 

[Trust]

@ CH , I think you didnt read well what I was writing : the center of the dish will be approx the same if you put it upside down .
Youre pictures dont show me messurements of that area .

 

[Channel Hopper]

Apologies, I thought picture 3 showed the dish, but it doesn't (not fully anyway)

On this Giberitni (a 1m in width, but not the usual affair) the dish height is 1.15m with the centre of the back plate offset approximately 45/60 cms to the reflector. The five bolt hole plate sits the dish much further forward than most I have used, in particular the Triax design you put on the test bench. This might also explain why it - looks as though - it would fit on the HtoH inverted, though I have not checked.

Commerical dishes such as the Prodelin , and I assume the Channel Master invert the reflector only to allow it to clear the post at low elevation angles retaining a similar loading on the king post, which is not apparent on the domestic dish designs, possibly because they are lighter materials and don't require the survivability guarantees

Certainly I would be hesitant to put in a Gibertini in a coastal environment, even this monster, regardless of the claims by the 'official' Gibertini dealer.

I will get some better pictures of the system in the next couple of days, tomorrow and wednesday are somewhat busy.

 

[Trust]

Did some experiments later this afternoon , with the Moteck SG2100 , its possible to attach the "elbow" pipe in reverse mode .
In that position its more convenient to attach the dish upside down without modding the dish elevation clamp (I think)
I believe that TM rotor is build the same way .
Since the Gibi has that long elevation clamp , it will also bring the receiving point a little higher , at the Triax ist was 105 mm .

 

[a33]

I have therefore propped the dish into the position to allow inverted reception, just clearing a shed opposite in the direction of Hotbird, and the measured difference in height to ensure the same signal is a little over 15.5 cms , or 6 inches in old money.

How did you measure the 15,5 cm?
It looks like 'height above the ground'?

So did you take this into account? :

When upside down, the new 'bottom' position is further from the pole, and must therefore be HIGHER, to be in the bottom edge of the beam!

The measurement should be done as Trust did, relative to the actual beam.

Also you did 'lift' the dish mount, to be able to get the proper inverted offset angle, if I understand you right? In that case the dish bolts are also automatically a little bit higher than with normal construction, so one or two cm should be subtracted from the 15,5.


Just saw the new post by Trust.
Nice testing! I thought of the possibility of the 180 degree rotated motor shaft, but didn't think about the new hight effect!
BTW The triax clamp can be mounted in two ways: 10-34* or 23-48*. Does that affect your measurement somehow?

What I did think about, is the 'length' of the AzEl-clamp: if the distance from motor shaft to back of the dish is bigger, in inverted mode the dish wil be higher, as you wrote! You were faster....


Greetz,
A33

 

[Trust]

I only have modded TDS dish clamps from my project Clover Project Clover - SatsUK
But its looks that if the clamp is mounted the other way , the necessary elevation cant be reached

 

[Channel Hopper]

As mentioned a few posts back, I have installed two dishes in the inverted position ( actually four since I now recall two others have been fitted 90 degrees from the vertical to lower the visual appearance from the front, they can be discounted however), and they are clearing the obstacles forward of them while still offering same signal on a lower pole height.

Yes, the HtoH motors with suspended support I have used in the past are all reversible , TM2600/Moteck/Alsat clones but I've not used them that way on geostationary stuff, only horizon scanning (wifi detection and an experiment on the 3.8m - remember the 'Vickers' post ?)

Thursday, if the weather is good and the country is not under martial law, I'll put the parts that are here on the roof and take some proper photographs to back up the earlier post(s)

 

[a33]

I just checked on the geometry of an offset dish:

When the elevation rotation axis of an AzEl mount is situated exactly in line with the line Center of dish face (C') to Deepest point of the dish (D), so that it lies exactly at the beam center line, then the received satellite beam of an inverted offset dish is exactly at the same height as that of a normally mounted offset dish.
See the attached picture, with the lines C' - D exactly in line, for both normal and inverted setup.

When the axis is situated higher up, e.g. behind the deepest point or behind the center of the dish, the inverted dish receives a HIGHER part of the beam. So in that case inverted mounting is advantageous: the higher the elevation axis is situated, the more advantageous.
This goes for a fixed mast, and also for a motor setup.

How much higher? For a fixed mast this could be calculated, with inputs:
1) distance dish face to elevation axis
2) distance top of dish to height of the axis (measured at dish face)
3) height of the dish
4) offset angle of the dish (or width of the dish, in combination with 3.)
Alas, 1 and 2 are not measured very easily (but not impossible!). So I'll leave the making of the formula to another time, or another person.

For a motor setup, the advantage diminishes the further you go from due south or due north, I assume. But I think even with a 90 degrees motor rotation, you would still have more than half of the advantage, I think.
But I'm not sure; I have difficulty to visualize the consequences of dish inversion in that situation. It might be dependant on the MOTOR-axis elevation angle, so on your site latitude, if I'm not mistaken.


On a motorized setup with a bend in the shaft, you can add an extra effect by changing the angle of the shaft bend, as Trust showed.
By that, the position of the dish elevation rotation axis relative to the height of the mast gets higher than in 'normal' position.
That would be the new starting point for the dish's elevation rotation axis, so there is your advantage...


I hope I've helped to clear things up a bit about the principle(s),

Greetz,
A33

 

[Red alert]

Thanks for the detailed information. Been very busy these days so not been able to look into it. Sounds complicated but even if I were to eventually setup inverted dish I dont think 15cm gain in height would help too much. Attaching a longer pole might be more straight forward. For now I will leave as it is and in the future if I have a south facing garden ill put up a 1.5m dish.

However it seems I have introduced a further error in my current setup, and as usual I need the forums help. I couldn't resist and tried to peak the signal further by seeing if I can fine tune the north\south axis of the mast, which was 0.2 of a degree out. In the process I made the pole 1 degree out north/south because I must have turned one of the turnbuckles too tight and it pulled one of the hook bolts out. Setup is still very stable and East/west remains in good alignment. I read that North/South doesn't really have to be spot on to follow the arc and we can make adjustments to the motor to follow the arc? What kind of adjustments are necessary if the north/south is out by 1 degree for example? I am picking up signal good in the middle of arc east of 1 west but declines from 26 east with 40% signal. 28 east is still 100%, 39 east is 47% max. I wont be able to use the modified motor angles because pole is not 100% on north/south? Should the motor angle still be my latitude even if 1 degree out?

Any help appreciated

 

[Channel Hopper]

North/south misalignment cannot be corrected by adjustments elsewhere.

 

[a33]

I read that North/South doesn't really have to be spot on to follow the arc and we can make adjustments to the motor to follow the arc? What kind of adjustments are necessary if the north/south is out by 1 degree for example?

You are absolutely right.
What counts is the motor axis angle due south, against the vertical. (So not against the pole!)
That you set at the (modified) motor elevation angle.
It follows that if the pole is 1 degree off, then the motor elevation as seen on the motor scale (if that would be precise...) must be compensated by 1 degree.
When you set it with an inclinometer, against the vertical, you just watch the inclinometer scale to get the (modified) elevation angle.

East/west nonplumbness of the pole is indeed BAD for following the arc.

Greetz,
A33

 

[Channel Hopper]

I am picking up signal good in the middle of arc east of 1 west but declines from 26 east with 40% signal. 28 east is still 100%, 39 east is 47% max.

Unless you confirm the west satellites are also off beam, this is not just a north/south misalignment, unless the turnbuckle that is no longer attached was exactly on the line.

Without the support of guylines all round the pole, you will also have the issue of gravity pulling the dish / motor assembly off as it tracks the arc, not so bad if it was the front line that broke.

 

[Red alert]

I am picking up signal good in the middle of arc east of 1 west but declines from 26 east with 40% signal. 28 east is still 100%, 39 east is 47% max.

Unless you confirm the west satellites are also off beam, this is not just a north/south misalignment, unless the turnbuckle that is no longer attached was exactly on the line.

Without the support of guylines all round the pole, you will also have the issue of gravity pulling the dish / motor assembly off as it tracks the arc, not so bad if it was the front line that broke.

I am unable to pick up sats west of 0.8 due to loss of line of sight. I can get 54% on 1 west but thats because approx 70% of the dish is visible on that satellite. When attaching digital level to pole, the east/west is off 0.2 degrees on left side and 0.1 degree on the right side. But overall I would say there is plumbness east/west. The turnbuckles on the east and west of the pole are fine.

@a33 thanks for that. Need to buy an inclinometer to set the angle. Is there a particular one to get for satellite dishes?