Tests of 120cm antennas

[Captain Jack]

I really do wish I had your hands and skills (and tools) to make the stuff you make, Rimant and Wim. Amazing...

 

[archive10]

I really do wish I had your hands and skills (and tools) to make the stuff you make, Rimant and Wim. Amazing...

Yes, very much so...
But even more baffling: I wish I had the *time* you guys obviously have for fiddling about!

Darned, I would love to do a spot of PIG welding in the garage now and then - or create a couple of LNB holders for experimentation....
I have to do my dish-mouting in the in-between moments of modern life with kids and wife...

Just feeling really envious here for a bit...

 

[Trust]

I really do wish I had your hands and skills (and tools) to make the stuff you make, Rimant and Wim. Amazing...

Then you will have 68 years old (but not shaking) hands .
But I still have to work ( 2 days /week ) at my employers plant (there is the lathe)

 

[humaxboy1]

It is indeed the OFC-1200P from HvdH and it did not make a lot difference .
I was surprised by the fact that the aiming point was above the center of that new type Laminas , it has 2 tubes and a plastic feedarm
Hans replaced the 2 tubes for 6 mm Inox treaded rods to lower the feedarm but by that , the lnb was pointing more up-high , therefore the lnb tilt-clamp
At the older version 1200 with the 3 tubes , that point was ± 10 cm lower .
And yes it was home-made by me .

Trust - this is really pioneering work what you are doing. What could be interesting for Laminas users is the extent of difference in signal when you us the new LNB holder . I am the owner of the older version of 120 and I have also replaced the 2 tubes with 6 mm Inox treaded rods (see the pictures)..it would be interesting using your home made LNB holder to see the possible improvement of the signal.

Humaxboy

 

[jase1]

It is indeed the OFC-1200P from HvdH and it did not make a lot difference .
I was surprised by the fact that the aiming point was above the center of that new type Laminas , it has 2 tubes and a plastic feedarm
Hans replaced the 2 tubes for 6 mm Inox treaded rods to lower the feedarm but by that , the lnb was pointing more up-high , therefore the lnb tilt-clamp
At the older version 1200 with the 3 tubes , that point was ± 10 cm lower .
And yes it was home-made by me .
@jase1 , cant remember which sat it was , but when it give improvement at one , it should be also for the other ones .

Was all the adjustment done by just tilting the LNB or did you need to adjust the dish too? Surely the the dish is already in the correct position and the adjustment was done to focus the LNB in on the whole of the dish.

 

[Trust]

We adjusted the dish elevation too , made a device to make that more accurate , it was very difficult to do exact without it .

 

[Archived-1]

made a device to make that more accurate

Great little device Trust, really would help trying to lock off nice i like it a little thought

 

[John]

... there really is a lot of brilliant ideas & construction going on by a lot of forum members on all sorts of subjects that really give guidance and are inspirational. What a fantastic forum

 

[jase1]

I really want to try this but I'm scared to death of adjusting the elavation on the dish and messing it up. Its wall mounted just below the gutter.
I'm ok on Nilesat at certain times of the day. I guess theres not much more can be done for 7W in the north west anyway.

 

[Riverblue]

On the subject of the aiming point of a lnb (particularly that of a 120cm Channel Master) I have read all the posts re parabola programs for calculations and carried out calculations and measurements myself. I have read a multitude of articles, in great depth, and I concur with Rima's view that the aiming point does appear that it should be slightly lower than it actually is if you assemble your dish as it was designed originally', i.e. as standard!
But, I still have this doubt that there is some aspect of wave pattern acceptance/design/signal compromise etc that us hobbyists just don't have enough knowledge of, which is why it has been designed as it is. Here is an extract from "Microwave Antenna Book" ‎www.qsl.net/n1bwt/app-6b.pdf


Now I can't find a reason for the feed to be aimed at the centre (I have only read about half of the book), but there obviously is a reason!

Now it will probably turn out that we can squeeze some more out of a CM dish by adjusting the aiming point and locating the phase centre of the lnb at the focal point of the dish, but even that may not prove that the dish was poorly designed, it may be an aspect of dish design that all manufacturers take in to account that we are not yet aware of!
We have to consider that these dishes have to work with a multitude of lnbs, potentially with different aperture angles and different f/D ratios so the final design might possibly be a "standard" industry compromise or an aspect of dish design that allows manufactures to cover these variables, a sort of "jack of all trades" approach?
Another thought is that the dish was designed 20 odd years ago, maybe technology has advanced and modern universal lnbs present different problems to frequency range specific lnbfs that were commonly used back then. Yes, I am aware that the "physics" will still be the same.
It might be worthwhile, if Rima can?, to include a matched Channel Master feed horn and lnb, possibly a modified IBU, in the comparison (yes, it becomes more complicated!)
It's all just food for thought!;)

 

[Riverblue]

I really want to try this but I'm scared to death of adjusting the elavation on the dish and messing it up. Its wall mounted just below the gutter.
I'm ok on Nilesat at certain times of the day. I guess theres not much more can be done for 7W in the north west anyway.

Maybe you should wait to see what the outcome is for others, if it is proven that gains can be made then adjust your dish accordingly!

 

[jase1]

Maybe you should wait to see what the outcome is for others, if it is proven that gains can be made then adjust your dish accordingly!

That sounds like a plan.

Whos up for it then ;)

 

[Riverblue]

That sounds like a plan.

Whos up for it then ;)

I think that this is one of those threads that will take a "while" to resolve completely. You will probably see more "action" with the onset of spring and fairer weather. Until then we can still talk . . . a lot!

 

[skomedal]

Might be out on a limb here, but an analogy between the eye and a satellite dish is that they both have focal/sweet spots.

The eye:-

The yellow spot or macula is an oval yellow spot near the center of the retina of the human eye. It has a size of 1.5 millimeters.

It is specialized for seeing things with highest clearness or visual acuity. It is the area of best vision where maximum amount of rod cells and cone cells are present.

http://simple.wikipedia.org/wiki/Yellow_spot

And the sat dish:-

The much talked about spot.

Which might be variable also

Just a theory as I suffer from astigmatism a refractive error of the eye in which parallel rays of light from an external source do not converge on a single focal point on the retina.

http://dictionary.reference.com/browse/astigmatism

As said just a thought.

Regards

 

[Trust]

I really want to try this but I'm scared to death of adjusting the elavation on the dish and messing it up. Its wall mounted just below the gutter.
I'm ok on Nilesat at certain times of the day. I guess theres not much more can be done for 7W in the north west anyway.

I know what you talking about , standing on a ladder with the full weight of the dish in one hand , the other at the wall and the wrench between your teeths and yor wife infront of the TV , disaster !

I do have a spare of that fine adjuster , if you will i can send it to you in a envelope weights 40 gr
Its just a M6x60 bolt with 2 extension nuts and 2 M6x12 bolts , you just have to drill two 6.5mm holes in the mount .

 

[hvdh]

Was all the adjustment done by just tilting the LNB or did you need to adjust the dish too? Surely the the dish is already in the correct position and the adjustment was done to focus the LNB in on the whole of the dish.

Yes, after every change of the LNB aiming direction, I fine-tuned the elevation. The Laminas then still was temporarily mounted on the balcony, with convenient access, but only a limited arc with free view. So I optimized only on weak transponders of Turksat, Azerspace, Yahsat-1A.

I am pretty sure for the OFC-1200P (with the new fat lower arm), the LNB aims a bit too high, i.e. halfway the dish height.
A small but real improvement (say, 0.2 dB S/N) comes by pointing lower (see the picture trust1 posted).

The side legs that I replaced with treads, allow extra fine adjustment, both in offset angle and symmetry in the horizontal plane. but not much varying in leg length is allowed. When more than + / - 1 cm, the lower arm/dish junction becomes too much stress and will probably deviate the dish shape at the bottom.

However, without the elevation fine adjustment on the bracket that trust1 made me, it was hard possible to do such fine adjustments in the first place! (edit: see photo by trust1 above this post)

 

[jase1]

I know what you talking about , standing on a ladder with the full weight of the dish in one hand , the other at the wall and the wrench between your teeths and yor wife infront of the TV , disaster !

I do have a spare of that fine adjuster , if you will i can send it to you in a envelope weights 40 gr
Its just a M6x60 bolt with 2 extension nuts and 2 M6x12 bolts , you just have to drill two 6.5mm holes in the mount .

View attachment 73630

Getting up the ladder doesn't worry me, not tracking the arc.........that's what I'm worried about

That's a really kind offer, Thank you. I don't think I'd be able to use it though as I'm using a 1224 motor.

At this moment in time I'm happy to just read this thread and try to take it all in.

 

[RimaNTSS]

Still continue to design better LNB holder for CM 1,2m . Right now already installed "object #5", will stop in it, I think, anyway it is raining outside and I can not step on the balcony to install antenna, seems that weekend be the same.
Holder is not INOX, so, going to be painted

 

[Archived-1]

I am unsure if you have tried drawing round the original holder Rimants then cut out the template, it will make it easy to fabricate, unless you are purposely wanting to move the lnb to a new position.

 

[RimaNTSS]

unless you are purposely wanting to move the lnb to a new position.

You bet, Martin. I am making my holders just for sack of tests. And if they work better than will replicate them out of INOX ;)