Tests of 120cm antennas

martin-f said:
I thought you was giving them away the other day.
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Why not. But they are not perfect. If I am making new ones that means I am not satisfied with old. So, basically, one installed on the dish will stay, but the rest is waste. Anyway, I need to practice welding :D
 
RimaNTSS said:
Why not. But they are not perfect. If I am making new ones that means I am not satisfied with old. So, basically, one installed on the dish will stay, but the rest is waste. Anyway, I need to practice welding :D
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Ok I get it now:) your only doing daily 120cm antennas laser pointing tests then ? :):D
 
Your fabrication work and welding is looking good Rimants keep at it same as me only practice makes perfect we can only get better :):-applause
 
Too much angle-grinding, too much. You will not believe, but all metal stripes I cut out of bigger pieces of metal by angle-grinder. And my working conditions in the garage are just terrible.
 
I did mention ventilation to you pal :), if your only messing with thin stuff like that it might be worth investing in a sheet metal hand cutter no fumes :)
 
I used to work in a car breakers yard from leaving school Rimants, I was only 16yrs old at the time 48 this year, and we bought an old lister engine cutting machine I think they call them jaws, well we called it that, it was and old looking thing then I am unsure of its age,

Well it would cut through 30mm solid bar like butter, not so much health and safety then, you had to watch what you was doing no room for mistakes :),

Anyway you can get little hand cutters/compressed air things, save your lungs :) but don't lose a finger :)
 
Nice sunny, clear cool morning here on the South Coast, ideal conditions in fact, so I have spent a couple of hours "fiddling" ;) What I have found with my 120cm Channel Master is as follows;
My lnb is approximately 29mm lower than calculated ideal!
The phase centre is 11mm short of calculated ideal!
The aiming point is central!
The skew of the lnb is 5.3°, dish pointer states 5.9°! (measured from mould line on lnb)
But
Moving the lnb toward the dish face lowers the signal!
Altering the skew slightly ( 0.6°) didn't give any gain!
Forcing the lnb (in it's holder) upwards, lowers the signal!(it pulls the dish face slightly out of shape because the arms are attached to the dish)
Loosening the lnb and aiming a bit lower didn't give any gain (not accurately aimed or placed)
So what does this mean? It suggests to me that as it is put together (standard) and with the lnb in the position it is placed by the design of the dish I am getting as much as I can out of it! (I didn't want to alter the elevation at this point because I went through all that when I installed it).
So what next? I can clearly see that my measurement of angles, position of the lnb etc are distinctly different from those calculated even though I feel I'm getting as much as I can out of it as it is! I suppose I'll have to make my own experimental adjustable holder just like others have, to see if the calculated position and aiming point of the lnb do actually make any difference, all the physics I've read suggest that it will, but we will see! I suppose any gain is worthwhile!;)
Something else that is blatantly obvious, is the need for another pair of hands to take photos, especially when trying to hold a straight edge, angle finder and take accurate measurements all at once!:mad:
 
I've painted some LNB holders last night. And painted they look like made of....... you will not believe!..... not polished INOX! :-rofl2
So, there is my plan: Next Sunday (can not do it on Saturday, as I go drinking fishing to the North sea) will take down Fibo 120 from my balcony and instead of it will erect CM 120.
 

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Misforming a dish has a hughe effect to the signal .
I know , to do proper tests you need eather a lot of hands (and eyes) or you have to make special equipment .
This week I replaced the laser pointer in my laser-lnb for a more powerfull one , the old one was not visable in a clear day .
With this laser-lnb its possible to receive and in the same time to project the aiming spot .
Also it has a extra long neck for a greater range to focus .
The lnb can easily twist in the feedhorn for skew adjustment .
Its a Inverto from the first generation , drilled a hole trough the circuitboard where the antenna was printed .
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RimaNTSS said:
I've painted some LNB holders last night. And painted they look like made of....... you will not believe!..... not polished INOX! :-rofl2
So, there is my plan: Next Sunday (can not do it on Saturday, as I go drinking fishing to the North sea) will take down Fibo 120 from my balcony and instead of it will erect CM 120.
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I see your welding skills are improving a big deal .
 
RimaNTSS said:
I start to suspect that there are 2 different types of feedarms available for the same dish: one to be used with original feedhorn and other for universal LNB.
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I thought that there was only one type of feed arm assembly for the "Type 120" dish that us hobbyists generally have, those that fix through the dish and link up at the lnb holder. Like so;
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They are fixed by bolts through the back;

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But now I've spotted these images of a slightly different arrangement, note the sidearms and how they are fixed to the lnb holder;

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It still looks like it is aimed at a central position to me! Also it looks like it gives more clearance for the attached feed horn.
Anyones else have feed arms like this on their Channel Master dish, or has seen one before? Does anyone think that the fact that it is probably (according to the logo!) an "Andrews" dish make any difference (which would make it newer!). Thought that they were all the same? :)
 
seen the side on arm,s before but on larger dishes with buc ect. the 3 dishes i have are all the standard type. the feed/lnb in your picture are c-band not ku-band
 
Anyones else have feed arms like this on their Channel Master dish, or has seen one before? Does anyone think that the fact that it is probably (according to the logo!) an "Andrews" dish make any difference (which would make it newer!). Thought that they were all the same? :)
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My dish has the flash on it. I also have the black LNB holder. So who knows....

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