A mystery worth solving ...

[Vipersan]

Ok ..as you all know I set up arc accurately in ku ..and am happy with it.
Not so happy with ka now I know about this odd error..
Below are some photos and db readings on the F15 for the same ka transponder ..
The lower db reading (over 1db ) is without the pole prop under the boom arm ..
and the reading over 8db is with the prop in place..
Ok you might think ..elevate the dish a little ..
Nope ..this never gets the over 8db result..
So ..I tried a bit of packing between the dish face and the boom arm ..where the meet and are bolted ..
Nope ..this makes it worse ..
So to me the boom arm is actually being flexed upwards relative to the dish face and against the side support struts ..
I doubt applying pressure upwards through the lift action of the prop would distort or change the dish in any way..
but whatever it is that's happening ...I WANT IT !!
Maybe some packing to physically lift the triple feed arm at the focal point ????
..this variation is negledgable in Ku ..but the shift is massive in Ka ..
with and without the prop..
..and the prop lifts the boom less than a cm..
A mystery to be solved methinks..
;)

 

[Analoguesat]

What would happen if you inverted the dish so gravity is working for you instead of against you?

 

[Vipersan]

What would happen if you inverted the dish so gravity is working for you instead of against you?

..Well I guess it would work ..but worth it ?? ..
I think making elements of the dish ..such as the side support arma adjustable is more practical ..
and perhaps diffent thicknessnes of packing at the focus where the triple feed is located ..
I _will_ solve this ..
I want that 1db gain in Ka....so I'll make it happen one way or t'other..
;)

 

[Analoguesat]

It would certainly be easier to make the side arms adjustable - should be reasonably easy to experiment using some slotted steel

 

[timo_w2s]

There's a certain point on my dish where if I apply a tiny bit of pressure I get an extra 0.5dB on 28.2E which can make some extra channels watchable at night. It's the only way I can get the extra signal so I've got a stick gently poking the dish in one corner now. You can't really see the dish face move it's so gental but it works...

 

[Channel Hopper]

With a large amount of weight stuck in front of it, the reflector is probably out of its natural parbolic shape.

Being an offest design has its advantages though since you can correct the parabola in two ways, the one you have already achieved in the vertical plane by compression, and by the opposite in the horizontal plane.

Easiest solution is to drill four holes in the side skirts, one above and one below each of the support arms, then tie some strong nylon line horizontally behind the reflector, pulling them as tight as possible by hand.

The straightening of the parabola can be achieved by using a torniquet motion using a simple piece of wood or metal , pulling the two pieces of nylon together and twisting them around each other to lock in place at the point where maximum signal is achieved.

 

[Vipersan]

..

With a large amount of weight stuck in front of it, the reflector is probably out of its natural parbolic shape.

Being an offest design has its advantages though since you can correct the parabola in two ways, the one you have already achieved in the vertical plane by compression, and by the opposite in the horizontal plane.

Easiest solution is to drill four holes in the side skirts, one above and one below each of the support arms, then tie some strong nylon line horizontally behind the reflector, pulling them as tight as possible by hand.

The straightening of the parabola can be achieved by using a torniquet motion using a simple piece of wood or metal , pulling the two pieces of nylon together and twisting them around each other to lock in place at the point where maximum signal is achieved.

Spot on CH ..
I can't really see to try this to full effect as it's too dark outside and just got out of the bath....but just tied a length of wire at the focus ..
threw it over the top of the dish stretched it tight and tied it off behind the dish to the steel tube I fitted on the H180 ..
then used some packing to apply a little more tension to the wire ..
removed the prop ..and the signal remained above 8.3db ..
Proving this method will work ..
Nice one CH ..
looks like we had the same approach in mind..
;)

 

[Vipersan]

Ok ..have something like this in mind ..
Self explanatory ...
Can anyone see a reason not to try this ?

I have plenty of strong Ally H section to make the frame..
rgds
VS

 

[dmaavrigdo]

I have found that a kitchen spatula can be a useful aid to test the aim of you lnb.Observing my signal strength while placing the spatula in front of the dish I noticed that when it was at the top of the dish there was an immediate drop but in the bottom 20cm there was no effect showing that my lnb was aimed too high.Further investigation revealed that the head of the bolt holding the lnb holder to the arm was pushing the horn of the lnb up when the lnb was all the way back.

 

[Channel Hopper]

Ok ..have something like this in mind ..
Self explanatory ...
Can anyone see a reason not to try this ?

I have plenty of strong Ally H section to make the frame..
rgds
VS

All profeshunal dish designs keep the reflector free from distortion

 

[gibertini]

same thing used to happen with my TD110 although i noticed it at 53east

 

[Trust]

Also with my 120 cm Fibo with the heavy load of the 3 lnb changer , the dish bended .
So i made 3 inox m8 rods at the backside .

 

[Vipersan]

Seriously fringe I know ..but it gives me hope ..
The Ka AZAM mux @ 7E locked at 7.7db for 3 seconds at 12:25 this evening ..
with the prop in place ..and clear skies..
Sadly not long enough to perform a scan on the F15 ..but I've never had above 6.3 db from AZAM ..and maybe you'll say ..so what ..
But it give me a buzz ..and the hope of more to come.
rgds
VS

 

[Trust]

I have found that a kitchen spatula can be a useful aid to test the aim of you lnb.Observing my signal strength while placing the spatula in front of the dish I noticed that when it was at the top of the dish there was an immediate drop but in the bottom 20cm there was no effect showing that my lnb was aimed too high.Further investigation revealed that the head of the bolt holding the lnb holder to the arm was pushing the horn of the lnb up when the lnb was all the way back.

With a laserpointer , adjustble angle , rotating in a bearing at the lnb holder , i can project a spot on the dish at the focus center .
At a few dishes , the spot is in the centre of the dish but mostly its lower .
Wenn i point the spot at the topside of the dish and rotate the pointer , the spot does not reach the edge downside at most of the dishes i tested .
Untill now only at the Triax TDS 110 and a Hirschmann ± 80 cm the spot follows the complete edge .
In the movies a TDS64 and the Laminas OFC-1200 showing how the lnb is looking at the dish .
For shure the openings angle of the feedhorn is more wider and has a lot of spillover .

 

[Vipersan]

Made a start and decided to go with steel ..at least for the 2 down braces ..one either side of the back-plate 27 inches long..
Yes this will be a bit heavier than ally ..but much more rigid..
at the bottom will be a hinged section between the 2 down braces ...and an adjustable support angle which can then be locked off to support the second boom arm running parallel to the original lnb boom..
Doing it this way I can build it in situte and wont have to take Carl down again..
The white upvc pipe you can see in one of the photos represents the second boom support arm..
rgds
VS

 

[Analoguesat]

Love the white wastepipe solution for keeping the cabling tidy! I may steal that idea next time I re-rig all the dishes!

 

[Channel Hopper]

Love the white wastepipe solution for keeping the cabling tidy! I may steal that idea next time I re-rig all the dishes!

Will a wastepipe groundstand be better than a tyre ?

 

[Archived-1]

I also see you have already come across the clued type VS, interesting work.

 

[Vipersan]

..Sadly got to go open the shop ..already 5 minutes late ..
but 1 downbrace done ...one to go
rgds
VS

 

[Vipersan]

Dammit ..it still goes dark wayyy too early..
Just managed about 50 minutes ..
Here is the project so far..
rgds
VS