2.4 Channel Master Offset

shriarun

shriarun

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Hi There

I did make temporary arms a few years ago for testing - from measurements that were given to me by a forum member on here. but he is now no longer a member .... i should still have those measurements on my p.c. somewhere - so will try to find them ... if you are wanting to make your own

There is a company in the u.k. called - Satellite Superstore - in the u.k. who sell them and the l.n.b. holder etc --- But they are pretty expensive to buy .... if you Google search that company name and look on their site you would find the arms etc under spare parts for 2.4 Raven dish.
Raven is the new name for all the old Channel master kit.

On this forum - member @RimaNTSS has made a very nice design of l.n.b. holder from stainless steel for channel master dishes that is dual purpose and can be used for k/u band or C band l.n.b,s ... my self and other members here have bought them from him ... they are very good. and i know he has made arms for his own dishes so may be able to give you help with the measurements etc ... if i cant find them here on my p.c. .... its been a while since i needed them - as i,m using the metalwork that came with my dish that supports the sub reflector arrangement again now and the side arms are a different length and design to the regular ones that you are most likely looking for .

It sounds from your post that you have just the large dish reflector and no metalwork or sub reflector.

regards ...
thanks for your feedback...Nelson sir i have checked that website they are selling much expensive including sending charges and customs charges resultantly it will become a huge amount ...moreover i can make myself if i get dimensions...i had made all back stand and front arms myself for my Prodolene 1.8 parabolic dish.. its result was quite satisfactory . i compared myself made with original ones..lets have a look at my self made fiberglass dish accesories.. ijust did hard work to refine accurate focal length ..however its costs about nothing too much.. but results is quite satisfactory....i really hope on the members of this great forum who will really help me
 

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RimaNTSS

RimaNTSS

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ijust did hard work to refine accurate focal length
You are right, it does not really matter what kind of feedarms and LNB-holder are installed to the dish, the most important is that LNB is located in such a way that LNB's phase center is co-located with antenna's focal point. BTW @shriarun, can I ask you a question.... what do you mean by "focal length of an offset dish" ? It is tricky question, as my next question will be what does F/D of an offset antenna means :rolleyes:. OK, just kidding :)
Perhaps this collage will help you to find the proper location of the LNB for your antenna
 

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nelson_b

nelson_b

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My Satellite Setup
Strong 4375 driving 1.8 C.M. offset + Inverto Black Ultra twin + BSC 421 and Zinwell C band l.n.b.,s - DR HD F15 - TM5302 and Skybox/Openbox M3 - HD receivers.+ other dishes in use - 2.4 CM offset - Alcoa 1.8 P.F. - C.M. 120.
My Location
north west yorkshire
thanks for your feedback...Nelson sir i have checked that website they are selling much expensive including sending charges and customs charges resultantly it will become a huge amount ...moreover i can make myself if i get dimensions...i had made all back stand and front arms myself for my Prodolene 1.8 parabolic dish.. its result was quite satisfactory . i compared myself made with original ones..lets have a look at my self made fiberglass dish accesories.. ijust did hard work to refine accurate focal length ..however its costs about nothing too much.. but results is quite satisfactory....i really hope on the members of this great forum who will really help me

Good morning - shriarun,

Thanks for your pictures .. I can see from them that you are more than capable of making your own support arms etc :-) ... so no need to spend lots of money on ready made parts.

As RimanTSS said the design of the arms and holder are not important ..... just the correct positioning of the l.n.b. the picture that he posted of position measurements for the different sizes of Channel Master dishes is probably all you need.

I will look for the original arm measurements later ... i,m not so organized with my satellite information on this P.C. - i,m sure i will still have the information somewhere ... l.o.l.
 
shriarun

shriarun

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Hotbirds ..eutelsat9.. Arabsat..Yahsat..Asiasat..Insat2e..Intelsat..Measat
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india
Good morning - shriarun,

Thanks for your pictures .. I can see from them that you are more than capable of making your own support arms etc :-) ... so no need to spend lots of money on ready made parts.

As RimanTSS said the design of the arms and holder are not important ..... just the correct positioning of the l.n.b. the picture that he posted of position measurements for the different sizes of Channel Master dishes is probably all you need.

I will look for the original arm measurements later ... i,m not so organized with my satellite information on this P.C. - i,m sure i will still have the information somewhere ... l.o.l.
yes Nelson and RimanTSS sir i know we need basically only focal length,side arms doesnt matter where we tighten..as i have alredy told previously when i made backstand and focal length,side arms i had all meausrements so it was quite easy for me to shape all parts in the same manner. it was xerox copy of original all what i made....i just update one more pic here so it will quite easy for all of you what i need.....Dear Nelson sir i know you have same brand dish so it is quite easy for you to measure..no need to find it in your pc
 

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Channel Hopper

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Geoffrey posted a technical drawing from the manual on this thread a decade ago


Somewhere else on the forum there is a link to the Type 243 antenna manual which I'm sure has the drawings on the back pages.
 
shriarun

shriarun

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anyhow thank u very much all of you who helped me a lot...
 
nelson_b

nelson_b

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Strong 4375 driving 1.8 C.M. offset + Inverto Black Ultra twin + BSC 421 and Zinwell C band l.n.b.,s - DR HD F15 - TM5302 and Skybox/Openbox M3 - HD receivers.+ other dishes in use - 2.4 CM offset - Alcoa 1.8 P.F. - C.M. 120.
My Location
north west yorkshire
yes Nelson and RimanTSS sir i know we need basically only focal length,side arms doesnt matter where we tighten..as i have alredy told previously when i made backstand and focal length,side arms i had all meausrements so it was quite easy for me to shape all parts in the same manner. it was xerox copy of original all what i made....i just update one more pic here so it will quite easy for all of you what i need.....Dear Nelson sir i know you have same brand dish so it is quite easy for you to measure..no need to find it in your pc
Hi -
I have not found the pictures and measurements of the regular l.n.b. support arms ...
But today i have been doing some C band l.n.b. test comparisons and have removed the sub reflector arms and support
and fitted regular arms again temporarily regular arms.jpg these are identical to the ones you looked at on the satellite superstore website ... if you wish i could take length measurements of these ?

Sub reflector arms and supports are very different and measurements of these are probably no use to you .13.jpg

Regards ...
 
Channel Hopper

Channel Hopper

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Hi -
I have not found the pictures and measurements of the regular l.n.b. support arms ...
But today i have been doing some C band l.n.b. test comparisons and have removed the sub reflector arms and support
and fitted regular arms again temporarily View attachment 127600 these are identical to the ones you looked at on the satellite superstore website ... if you wish i could take length measurements of these ?

Sub reflector arms and supports are very different and measurements of these are probably no use to you .View attachment 127602

Regards ...
A rare beast indeed Nelson.

 
RimaNTSS

RimaNTSS

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i know we need basically only focal length
As you still continue to say this term, could you please explain what do you mean by "focal length"? Distance from where to where?
 
shriarun

shriarun

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Hotbirds ..eutelsat9.. Arabsat..Yahsat..Asiasat..Insat2e..Intelsat..Measat
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As you still continue to say this term, could you please explain what do you mean by "focal length"? Distance from where to where?
RimaNTSS ..really sorry to say..i think u took it wrong...basically i am approximate familiar regarding very basic terminolgies of dish antenna..focal length for me refers to distance of surface of dish antenna esp centrte and lnb where wave length gets focuses by all sides...

respected Nelson and RimaNTSS..i have marked on the dish image given below i need these measurements...especially from bottom surface to LNB clump...if i get these accuratly .it will become easy for me to made ..

with deep regards...
 

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nelson_b

nelson_b

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Messages
1,729
My Satellite Setup
Strong 4375 driving 1.8 C.M. offset + Inverto Black Ultra twin + BSC 421 and Zinwell C band l.n.b.,s - DR HD F15 - TM5302 and Skybox/Openbox M3 - HD receivers.+ other dishes in use - 2.4 CM offset - Alcoa 1.8 P.F. - C.M. 120.
My Location
north west yorkshire
RimaNTSS ..really sorry to say..i think u took it wrong...basically i am approximate familiar regarding very basic terminolgies of dish antenna..focal length for me refers to distance of surface of dish antenna esp centrte and lnb where wave length gets focuses by all sides...

respected Nelson and RimaNTSS..i have marked on the dish image given below i need these measurements...especially from bottom surface to LNB clump...if i get these accuratly .it will become easy for me to made ..

with deep regards...
O.k. - shriarun
I,m out most of the day tomorrow and Tuesday morning and its already dark here now - today ...
If the weather is dry on Tuesday afternoon i will accurately measure the arm lengths etc -- with pictures -- before i put
the Sub reflector arms and support back on.
regards
 
nelson_b

nelson_b

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1,729
My Satellite Setup
Strong 4375 driving 1.8 C.M. offset + Inverto Black Ultra twin + BSC 421 and Zinwell C band l.n.b.,s - DR HD F15 - TM5302 and Skybox/Openbox M3 - HD receivers.+ other dishes in use - 2.4 CM offset - Alcoa 1.8 P.F. - C.M. 120.
My Location
north west yorkshire
respected Nelson and RimaNTSS..i have marked on the dish image given below i need these measurements...especially from bottom surface to LNB clump...if i get these accuratly .it will become easy for me to made ..
Hi - A couple of questions
Do you already have an LNB holder for the dish . or do you intend to make one ?
And - just curious - do you intend to use the dish for K/U band reception or C band ?
 
shriarun

shriarun

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Hotbirds ..eutelsat9.. Arabsat..Yahsat..Asiasat..Insat2e..Intelsat..Measat
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Hi - A couple of questions
Do you already have an LNB holder for the dish . or do you intend to make one ?
And - just curious - do you intend to use the dish for K/U band reception or C band ?
dear Nelson i will use it for ku band...still i have reflector only..not a single nut bolt..its accessories making isnt a challange ...i just acurate lengths for ku band...
 
nelson_b

nelson_b

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My Satellite Setup
Strong 4375 driving 1.8 C.M. offset + Inverto Black Ultra twin + BSC 421 and Zinwell C band l.n.b.,s - DR HD F15 - TM5302 and Skybox/Openbox M3 - HD receivers.+ other dishes in use - 2.4 CM offset - Alcoa 1.8 P.F. - C.M. 120.
My Location
north west yorkshire
dear Nelson i will use it for ku band...still i have reflector only..not a single nut bolt..its accessories making isnt a challange ...i just acurate lengths for ku band...
O.k - Thanks for the reply ..
I hope to get time to measure lengths of arms tomorrow afternoon.
 
A

a33

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focal length for me refers to distance of surface of dish antenna esp centrte and lnb

Only with prime focus dish, this 'center of dish' is right.

'Focal distance' is a property of a parabola: distance from vertex to focal point.
Only with a prime focus dish, the vertex is at the center of the dish. So for a prime focus dish, your statement is right.

With an offset dish, the focal distance is also the distance between focal point and vertex; where vertex means: center of 'mother prime focus dish', where the offset dish 'is cut-out from'. Usually the vertex is not on the offset dish, but below!
You are not the first (alas), to use the term confusingly.

For offset dishes, there is also an "effective focal length", used e.g. for multifeedcalculations. But this also has nothing to do with the center of the dish; it is distance from focus to "G-spot" (where bisector line between dishtop to focus to dishbottom, crosses the dish surface).

The f/D-ratio also uses the proper focal distance to vertex.
For a prime focus dish, there is a simple, straight-forward relation between f/D-ratio and illumination angle of the LNB feedhorn.
For an offset dish, the relation is quite a bit more complicated. For better comparison of illumination angles, sometimes the term 'f/D-equivalent' is used, and calculated in a different way than f/D. However, using the illumination angle value is least confusing, I would say.


Here endeth the lesson....... :confused Thanks for your attention......

greetz,
A33
 
RimaNTSS

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However, using the illumination angle value is least confusing, I would say.
For antenna I more like to use term "opening angle" , but "illumination angle" is belonging to LNB's properties.
 
nelson_b

nelson_b

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1,729
My Satellite Setup
Strong 4375 driving 1.8 C.M. offset + Inverto Black Ultra twin + BSC 421 and Zinwell C band l.n.b.,s - DR HD F15 - TM5302 and Skybox/Openbox M3 - HD receivers.+ other dishes in use - 2.4 CM offset - Alcoa 1.8 P.F. - C.M. 120.
My Location
north west yorkshire
@shriarun
Here are some pics to show how the regular arms look on my dish and how they are fastened to the current l.n.b holder -
regular arms.jpg 1.JPG2.JPG

pics below showing measurements etc ...
First pic shows how far the bottom arm goes into the clamp on the bottom of the dish.
next pic shows full length of bottom arm - it passes the dish face at 58 and one quarter inch ... and ends at 60 and one quarter inch
Next pic shows side arm connection to dish - passes dish face at 78 and one quarter inch and bolts to dish at 79 and three quarter inch
3.JPG 4.JPG5.JPG

This should help you to get somewhere near the place for the l.n.b .. the rest is down to the design of your k/u l.n.b. holder ...

the measurements (in red ) on the pic that Rimants posted in post 122 should help to get the l.n.b. into the correct distance and angle position in relation to the dish face . and save some trial and error finding the "sweet spot" l.o.l.

I prefer to use the l.n.b. holder that i got from Rimants as it fully adjustable and will take k/u/ or c band l.n.b,s unlike the channel master fixed clamps
Cheers ....
 
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shriarun

shriarun

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Messages
17
My Satellite Setup
Hotbirds ..eutelsat9.. Arabsat..Yahsat..Asiasat..Insat2e..Intelsat..Measat
My Location
india
@shriarun
Here are some pics to show how the regular arms look on my dish and how they are fastened to the current l.n.b holder -
View attachment 127763 View attachment 127764View attachment 127765

pics below showing measurements etc ...
First pic shows how far the bottom arm goes into the clamp on the bottom of the dish.
next pic shows full length of bottom arm - it passes the dish face at 58 and one quarter inch ... and ends at 60 and one quarter inch
Next pic shows side arm connection to dish - passes dish face at 78 and one quarter inch and bolts to dish at 79 and three quarter inch
View attachment 127778 View attachment 127779View attachment 127780

This should help you to get somewhere near the place for the l.n.b .. the rest is down to the design of your k/u l.n.b. holder ...

the measurements (in red ) on the pic that Rimants posted in post 122 should help to get the l.n.b. into the correct distance and angle position in relation to the dish face . and save some trial and error finding the "sweet spot" l.o.l.

I prefer to use the l.n.b. holder that i got from Rimants as it fully adjustable and will take k/u/ or c band l.n.b,s unlike the channel master fixed clamps
Cheers ....
thank you very much Nelson Sir...heartly thanks
 
nelson_b

nelson_b

Contributor
Messages
1,729
My Satellite Setup
Strong 4375 driving 1.8 C.M. offset + Inverto Black Ultra twin + BSC 421 and Zinwell C band l.n.b.,s - DR HD F15 - TM5302 and Skybox/Openbox M3 - HD receivers.+ other dishes in use - 2.4 CM offset - Alcoa 1.8 P.F. - C.M. 120.
My Location
north west yorkshire
thank you very much Nelson Sir...heartly thanks
Some additional info ... a few pics of two types of Channel master fixed K/U holders ..
The metal one only accepts a genuine Channel master feed horn for C120 l.n.b.,s
The hard black plastic one will accept regular l.n.b.,s .... and has spacers so that the C.M. feed horn for C120 l.n.b.,s can also be used.

DSC01766-Optimized.JPG DSC01767-Optimized.JPG DSC01768-Optimized.JPG DSC01770-Optimized.JPG

I look forward to seeing some pictures posted on the forum of your 2.4 dish in full working order ...
and some reception reports .... :cool:

Regards ....
 
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