Advice Needed Adding C to a 1.2 Channel Master.

aceb

aceb

Specialist Contributor
My Satellite Setup
TBS 6925
1.8m Precision + PLL Bullseye, motorised but probably siezed now.
2 x Sky Zone 2 for 28/19/13°E
My Location
Sussex
Can it be done, has anyone done it? Is it possible to fit a C band LNB with conical scalar to one side of an Inverto BU on a CM 1.2 and get any worthwhile results approaching what you'd get with the C LNB on its own at the sweet spot?
 
aceb said:
Can it be done, has anyone done it? Is it possible to fit a C band LNB with conical scalar to one side of an Inverto BU on a CM 1.2 and get any worthwhile results approaching what you'd get with the C LNB on its own at the sweet spot?
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Basically - Yes. But never tried it. Worthwhile results - Errr .. you will get results of a kind but worthwhile = ??. Better results if mounted at focal point and sacrifice some performance on the Ku lnb by mounting that in an off-set position. Have you any particular Cband transmission in mind that you wish to capture ?.
 
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Yes, the beamwidth of something as small as a 1.2 at sub 5GHz frequencies means it is possible, but you might find a scalar feed with integral Ku section (ala the Chapparal Bullseye ) will give you slightly better results as the focal points are closer. You will need to invert the dish to maintain water integrity though.
 
aceb said:
Can it be done, has anyone done it? Is it possible to fit a C band LNB with conical scalar to one side of an Inverto BU on a CM 1.2 and get any worthwhile results approaching what you'd get with the C LNB on its own at the sweet spot?
Click to expand...
Disregarding the signal drop-off from off-setting your C-band LNB, the practical problem with the Channel Masters are that the feed-support arms will be in the way.
The feed-arm design means that anything left or right of the central point has the feed-support arm right in front of it.

Ways around this include doing a "Stuka", where you rotate the feed-support arms slight downwards, and attach an extension to the original bracket, and then attach the side-loaded LNBs to the central LNB. This has been done by several members (past and present) of this forum, so wait around for replies, or go check out some older threads.
Another approach is doing a new feed-arm design (like @RimaNTSS), with a square feed-arms, and feed-support arms that attach much closer to the dish face than the original CM design. Effeciency depends on the mount and dish you have, and how much mechanical engineering prowess you have.

I would try the Stuka first, then decider if worthwhile to try a new arms design...
 
LNB-rotation mechanism is much better than any multifeed. Depending on the band, the mechanism will place C, Ku or any other LNB directly in the focus of the antenna. It is possible to widen side arms little bit to be able installing 2 LNBs side by side without feedarms obstructing the view, but there is no simple solution to make it. Want it good and simple- install 2 dishes, one for Ku, another one for C.
 
Two dishes aren't an option sadly, if they were I think he'd have something much larger but that's not an option either as the site is very VERY exposed and would require structural work to support a base heavy enough to hold down a 1.8 or 2.4M. I'll try some searches to see if I can find some photos of the previous attempts to get an idea of where it needs to be and how tricky it is to do. I know what's available on a 1.2 on C band from my days with the Precision but not sure how much it drops off by offsetting the LNB. LNB rotation would be perfect @RimaNTSS but is beyond my level of engineering skill.
 
Some time ago I was trying to make multifeed on CM 1.2m, but, as I've said earlier, I do not see easy way to do it. I think if you go this way, it would be possible to install C and Ku-band LNBs and side-feedarms will not obstruct the reception. IMG_20160823_155914 (Large).webp
 
There's a multi-feed kit that you sent me a while back, Paul, that could be used for this........... Though, as I found out, it's a pretty flimsy system. On my 1.8m, I have the C band LNB right above the Ku and I use the declination control to focus it. Not as good as in focus (LNB rotator etc.) but it's more than good enough.
 
Or maybe even an attempt at ... Art?

I mean displaying the small portion of flimsiness with which a good design can be made totally disgusting as a piece of value kit?
If the "extensions" were removed, I expect the dish would function just as new. But at 499 USD I would still hesitate...
 
I believe that parabola calculation for that dish , shows that the lnb aiming point , is a bit lower than with the lnb holder at factory position .
Maybe thats the reason why they made it that ( unproffesional) way .
 
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