Channel Master 1,8m feedarms

[RimaNTSS]

Will start new tropic on the old issue. Here I wish to describe how I will make new feedarms for my 1,8m CM dish. And not only the feedarms, but also integrated LNB changer. Will provide pictures and description as much as possible. Who knows, maybe that will be helpful to other users. If somebody wishes you can go along and share other opinions about technical details. This is probably going to be long topic, as I am not in the hurry. So, will start from bottom fix of the new feedarm.. found small piece of square tube and cut piece out of it, then added more metal parts to it. Will make bottom feedarm out of 40x15x1,5mm pipe. Side arms will probably be made out of ~15mm tube (do not have it in stock).

 

[archive10]

I'm sure whatever you come up with is more robust, adjustable, versatile, and more rust-resistant than my first attempt

With an LNB changer, a challenge is the accumulated weight hanging off the LNB arms.
Certainly, the standard stuff won't cut the muster ... (the Rx/Tx version has more substantial mount, of course).

Making it a Gregorian would move the weight closer to the reflector.. maybe use a sub from a Fibo?
Or even try using the sub from the 4.6 on the 1.8 ... that would be a bit of a project, though... ;)

 

[RimaNTSS]

No, this time no SUBs, just simple offset dish with LNB-changer and motor (Fibo) behind the dish.

 

[samoloko]

Rima

why not make a fibo sub upgrade to Improve Channel Master 1.8 gain

 

[RimaNTSS]

why not make a fibo sub upgrade to Improve Channel Master 1.8 gain

I could do that, but then LNB-changer will not be part of the project. Of course, it is possible to use Fibo SUB for C-band, because of big size of C-band feedhorn performance would not be high. So, this time I will concentrate on simple offset antenna design. Worked on side arms connection today. It looks like this on the original set-up
I cut 4 pieces of metal, 6 screws (made them headless), drilled some holes, welded little bit and made it look nice. Drilled couple of additional holes in the dish and attached new elements to it

 

[RimaNTSS]

Installed support for bottom feedarm and also made junction for side-arms connection to the bottom feedarm. Sounds complicated but pictures can explain better

 

[RimaNTSS]

New sidearms made out of 12mm pipe. From each side welded halve of 8mm long nut. In each side there is ~20cm long threaded bar goes in. Those feedarms are fully adjustable. Should work fine. Inside the bottom feedarm axis (out of 12mm pipe) will be located.

 

[Captain Jack]

Fantastic!

 

[Anonymous_1]

Where is the button to purchase the same for my 2.40m CM ?...
I need to replace the sub reflector and this huge professional mount and feedarms by something lighter.

 

[archive10]

Where is the button to purchase the same for my 2.40m CM ?...
I need to replace the sub reflector and this huge professional mount and feedarms by something lighter.

May @RimaNTSS needs to start a little production workshop - I need a set of feedarms for my 2.4 meter Prodelin 1241.
(Although they would have to be longer than yours - the CM has an f/D of 0.6, the Prodelin is 0.8)

 

[RimaNTSS]

I need to replace the sub reflector and this huge professional mount and feedarms by something lighter.

Show exactly which parts you wish to change, if they are not so big we could work it out.

 

[archive10]

New sidearms made out of 12mm pipe. From each side welded halve of 8mm long nut. In each side there is ~20cm long threaded bar goes in. Those feedarms are fully adjustable. Should work fine. Inside the bottom feedarm axis (out of 12mm pipe) will be located.

From the last picture: Your CM180 arms seems to be a bit long... are you sure they give roughly the same LNB position as the standard ones?

 

[RimaNTSS]

Original CM 1.8m side feedarms are about 1,5m long. I made new arms also 1,5m, but, taking in account that I will probably be willing to install LNB changer and maybe also subreflector at some point of time, then longer feedarms are needed to lower bottom-feerarm even more.

 

[archive10]

Original CM 1.8m side feedarms are about 1,5m long. I made new arms also 1,5m, but, taking in account that I will probably be willing to install LNB changer and maybe also subreflector at some point of time, then longer feedarms are needed to lower bottom-feerarm even more.

Of course - the original arms are meant to meet roughly where the LNB is, whereas your custom ones (just like the Rx/Tx version from CM) needs to be lower to accommodate the feed plinth.
Just seemed to be much longer, and more like the 0,8 f/D dishes...

 

[RimaNTSS]

Not a big deal, if find them too long it is always possible to shorten them (make them longer is possible as well but nit so easy).

 

[Anonymous_1]

Show exactly which parts you wish to change, if they are not so big we could work it out.

Thanks for your proposal
For this antenna, I don't need a LNB changer, I just want to be able to easily change LNBs (C, KU, KA, X, S) manually, this antenna is more for testing than regular DX.

First of all, I'd like to replace this LNB holder and the subreflector by a regular LNB holder, maybe reused the feedarms or replaced them..
In a 2nd time, I will check if I can use the EGIS motor (I must consider adding a polarotor )

If someone has a better idea, I am "open"

PS: no need to mod the cat

 

[RimaNTSS]

@Feedsat_DXer I think you can live with all original feedarms, you just remove SUB and LNB. Focal point of your antenna located approximately where I made yellow circle. So, all you need is new LNB-holder (painted green). You can get idea from the attached pictures. Maybe it is better to install 63mm clamp to be able to fit C-band LNB, and then, in the same clamp some spacers can be added for smaller LNBs.

 

[Anonymous_1]

Thanks rima for the pics and your idea.
I have to think about it and test it.