Just Sharing This Coming to a forum near you soon - mobile dish test rig

nelson_b said:
Sorry John .. my test rig -1.8 setup is dismantled currently ... if i get time i will lean the dish against the garage wall and put the arms and holder back on ... i,m looking at a holiday in NW Scotland next week if the weather comes good - and have a lot to do before leaving though ...
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No worries chap, just a curiosity thing :Y
 
RimaNTSS said:
Nice sticker @John . I see that you've set aiming point of the feed little bit too high (red dot). It should be ~10cm lower (green dot) IMHO.
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Further to Rimants observations, it got me curious re: the accuracy of the CM 1.8 stock install as straight out of the box.
This dish never got used in stock mode - the feed support was a custom built thing to take a rotating lnb changer.
The previous pictures showing the illumination landing spot is with a correctly installed set of arms and CM feed that came with the dish.
Tonight i rushed up a temp laser marker fixed onto the end of a 40mm short tube that fitted the CM feed holder at the focal point - most people would take the view that if you did a careful feed install of a highly rated dish, that you can't really get it wrong due to everything being pre-drilled etc etc and that it would be spot on - - well here's the results video of a quick illumination check

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... And here's the stock illumination pattern on a diagram
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CM 1.8 poor stock illumination.....webp
 
Terrible that Channel Master could have produced such a poor product.

I’ll give you £50 for it , delivered to Surrey :p
 
Channel Hopper said:
Terrible that Channel Master could have produced such a poor product.

I’ll give you £50 for it , delivered to Surrey :p
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Hmmmm , tempting

There's got to be a valid reason for that test result which i would love to know - the dish feed arm components are all untouched / unmodded from new and bolted into the pre-drilled holes of the dish fixing points. The laser was at the focal point and rigid in the 40mm tube holder which was a good fit and the top half of the lnb clamp was only just loosened off very slightly to allow to turn through 360°.
Lets have some theory's then folks
 
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Wrong/incorrectly manufactured (too short) feedarm supplied with dish?
 
jeallen01 said:
Wrong/incorrectly manufactured (too short) feedarm supplied with dish?
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+1
I would go along with that.

It looks like the pattern issue could be resolved if the illumination map was lowered. A longer bottom feed arm might pivot the illumination pattern to be better aligned on the dish. You could try some type of shim to extend it a centimeter or two an see what happens with the illumination map.
 
moonbase said:
+1
I would go along with that.

It looks like the pattern issue could be resolved if the illumination map was lowered. A longer bottom feed arm might pivot the illumination pattern to be better aligned on the dish. You could try some type of shim to extend it a centimeter or two an see what happens with the illumination map.
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Pretty much my thoughts when I posted earlier.
 
moonbase said:
+1
I would go along with that.

It looks like the pattern issue could be resolved if the illumination map was lowered. A longer bottom feed arm might pivot the illumination pattern to be better aligned on the dish. You could try some type of shim to extend it a centimeter or two an see what happens with the illumination map.
Click to expand...



... Yep could do that, i'm not worried about correcting the illumination pattern at this stage, i'm more intrigued as to why it is.
Thinking about it - when the dish package got delivered it came in two consignments - - a separate box for the reflector and a separate box containing the feed arm & feed assembly. I wonder if there was some slight manufacturing change at some stage between the dish and accessories ?? .. CH / Rima ?
 
John said:
... Yep could do that, i'm not worried about correcting the illumination pattern at this stage, i'm more intrigued as to why it is.
Thinking about it - when the dish package got delivered it came in two consignments - - a separate box for the reflector and a separate box containing the feed arm & feed assembly. I wonder if there was some slight manufacturing change at some stage between the dish and accessories ?? .. CH / Rima ?
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OR, "they" sent you the wrong feed arm and feed assembly?
 
... here's my measurements of component parts compared to Rimants ref: picture
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Ref: - A to G = 1186. - - - My A to G = 1061
Ref: - G to F = 1221. - - - My G to F = 1250
Ref: - A to F = 1830. - - - My A to F = 1835
Ref: - B to F = 2080. - - - My B to F = 1100
Dish depth = 172.2 - - - My D/Depth = 172.2

** Rima, can you please clarify your ref: dimension B to F on your file - my file pic has that measurement slightly obstructed.
CM Dish info - RimaNTSS.webp
 
The reflector / feed arm dimensions will not have changed in the whole lifetime of the Channel Master design so it is unlikely to be a mis-delivery of parts, unless there is a clone package out there from a third party manufacturer (capitalising on the lack of spares and US ordering issues in the mid 2000s)
If the focal point does tie in with the technical drawing, you might have a clone clamping assembly, where the 'angle of dangle' is incorrect.
 
Channel Hopper said:
The reflector / feed arm dimensions will not have changed in the whole lifetime of the Channel Master design so it is unlikely to be a mis-delivery of parts, unless there is a clone package out there from a third party manufacturer (capitalising on the lack of spares and US ordering issues in the mid 2000s)
If the focal point does tie in with the technical drawing, you might have a clone clamping assembly, where the 'angle of dangle' is incorrect.
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.. Good point
.. i do have an 'angle of dangle' issue - but that's another story
 
John said:
... here's my measurements of component parts compared to Rimants ref: picture
..........................................................................................................................................................................................................................................................................................................
Ref: - A to G = 1186. - - - My A to G = 1061
Ref: - G to F = 1221. - - - My G to F = 1250
Ref: - A to F = 1830. - - - My A to F = 1835
Ref: - B to F = 2080. - - - My B to F = 1100
Dish depth = 172.2 - - - My D/Depth = 172.2

** Rima, can you please clarify your ref: dimension B to F on your file - my file pic has that measurement slightly obstructed.
View attachment 126280
Click to expand...
Ref B to F - looks like the nominal should obviously be 1080 and not 2080 (latter would make no sense at all - LNB would be 2m from the dish, and the support arms would then be far too short !) which corresponds quite closely to your own measurement.

Thus, judging by CH's comment/question about the "angle of the dangle" of the LNB and the close-up of it, I'm guessing that that does seem to be where the source of the issue actually lays.
 
Guys! It is interesting discussion, I like it. But I am away from home till tomorrow evening, receiving notifications on cell phone. Will say what I think about it later. In two words: CM feedarms&LNB-holder design does not hold LNB in correct position and it should be corrected in one or the other way IMHO. Why is that? I do not know :-doh
 
To satisfy my / our curiosity i thought i would knock together a jig based on the ref: dimensions for a 1.8 CM from Rimants data - i will re-construct the original CM feed arms / feed etc tomorrow along side the jig to get a difference comparison.
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Ref; Jig. B .. reduced..webp
 
Might be a good idea to ask Wim too, as he did all the measurements on the 1.8 CM when he constructed the LNB changers some time back...
 
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