Advice Needed King post modification 76mm to 80mm for bigger antenna.

[zorrin]

Hello, I currently have a Channel Master 1m20 with its original polar mount on a kingpost that I had made.

the diameter is 76mm, the thickness is 3mm and the height is 2m.
There are 4 fin reinforcements of 80mm by 10mm over a length of 1m50.





The base is 250X250mm by 10mm and is fixed to the ground by 8 threaded rods in M12 taken in a concrete block of 250Kg.




I have a 1m80 to 2m60 prime focus antenna like this one :



On the notice it indicates that it takes a tube of 80mm in diameter.




my idea is to take an 80mm tube on a 50cm slot and 2mm thick, cut it lengthwise and insert it on the 76mm tube.
Fix the two tubes together and install the large antenna.

Do you think it's enough for an antenna of 1m80 and if possible 2m60?

 

[RimaNTSS]

I would say, you can try to install 1.8m dish. But, in fact, this is a common issue... I think if some time ago you think about something more universal, you would install something like I have done. In such stands, I can install any dish I wish, and, in addition, make installation plumb.

 

[zorrin]

I would say, you can try to install 1.8m dish. But, in fact, this is a common issue... I think if some time ago you think about something more universal, you would install something like I have done. In such stands, I can install any dish I wish, and, in addition, make installation plumb.

I know RimaNTS, you're right I didn't think enough.

It was the height of the king post that scared me and I especially wanted to solidify the 2m x 76mm tube.
Now after 1 year I see that it is very solid and I can see myself putting the big antenna.

So, for you the 2m60 are too much for my installation?

 

[RimaNTSS]

the 2m60 are too much for my installation?

I do not know. Of course, you can try, and if you see the dish wobbling too much, you can always add some reinforcement. You can not know before you try.

 

[nelson_b]

I have a 1m80 to 2m60 prime focus antenna like this one :

View attachment 142130

On the notice it indicates that it takes a tube of 80mm in diameter.

View attachment 142131


my idea is to take an 80mm tube on a 50cm slot and 2mm thick, cut it lengthwise and insert it on the 76mm tube.
Fix the two tubes together and install the large antenna.

Do you think it's enough for an antenna of 1m80 and if possible 2m60?

An "Alcoa" 1.8 ..... Nice dish .... do you have the extension panels for it too ?

I have one of these dishes currently in storage ... but i don,t have extension panels for mine :-(
i,m hoping to put mine back in use again later this year .

 

[zorrin]

An "Alcoa" 1.8 ..... Nice dish .... do you have the extension panels for it too ?

I have one of these dishes currently in storage ... but i don,t have extension panels for mine :-(
i,m hoping to put mine back in use again later this year .

Yes, I have the extension panels.
I found it new 5 years ago I think.
Never used, still in boxes for more than 20 years.
Originally I did not know that there were possible extensions.
The most incredible thing about this antenna is the weight of the polar mount, it is so heavy.

Now I really want to install it.

 

[nelson_b]

You are a lucky man to have found a new one of these dishes ... and to have got extension panels for it too
Mine has just a fixed AZ/EL mount and it is very substantial ... i will dig out some pictures another day and post here. i converted mine to a C band l.n.b holder last time it was in use ... and it worked well

Sats Uk member " Vipersan " has one of these dishes too - his has got the polar mount like yours ... i,v worked on it with him in the past and i can agree with you -- the polar mount is very strong and heavy ... He made some half sized extension panels for his dish. using glass fiber matting and resin .... and got quite good results with them too.

 

[zorrin]

You are a lucky man to have found a new one of these dishes ... and to have got extension panels for it too
Mine has just a fixed AZ/EL mount and it is very substantial ... i will dig out some pictures another day and post here. i converted mine to a C band l.n.b holder last time it was in use ... and it worked well

Sats Uk member " Vipersan " has one of these dishes too - his has got the polar mount like yours ... i,v worked on it with him in the past and i can agree with you -- the polar mount is very strong and heavy ... He made some half sized extension panels for his dish. using glass fiber matting and resin .... and got quite good results with them too.

I got it for free when an antenna installer sold his business.
I went there for visiosat 90 and bisat and I came back with it as well.
Compared to my information, do you think that my king post after modification would resist to the antenna in version 1m80 or 2m60?

 

[nelson_b]

I got it for free when an antenna installer sold his business.
I went there for visiosat 90 and bisat and I came back with it as well.
Compared to my information, do you think that my king post after modification would resist to the antenna in version 1m80 or 2m60?

Wow - you got it for free too ....
Your king post looks very substantial ... and the modification sounds good so ... yes i think so ...
As RimaNTSS said you can always add some reinforcement later if you decide its needed.

 

[zorrin]

For 1m80 I have no doubts.
For 2m60 it's another story I think. But I would really like to tell myself that it's good.
We await further reactions.

 

[Manikm909]

nice dish colour @zorrin

 

[zorrin]

nice dish colour @zorrin

I would only say one thing, it's your fault

 

[zorrin]

@Channel Hopper do you think it is possible with this modification to go to 1m80 or 2m60?
On the documentation of my antenna they do not speak of the passage from 1m80 to 2m70 for the tube...

 

[Channel Hopper]

Of course it will work.

How long it stays up there is another question.

Here is the formula to calulate the wind loading of a mesh dish (add 50% to the final figure for a solid prime focus and 60% for an offset that is non inverted)

XRT-C | Wind Loading Calculations with a Radio Telescope

www.xrt-c.co.uk

 

[moonbase]

Sats Uk member " Vipersan " has one of these dishes too - his has got the polar mount like yours ... i,v worked on it with him in the past and i can agree with you -- the polar mount is very strong and heavy ... He made some half sized extension panels for his dish. using glass fiber matting and resin .... and got quite good results with them too.

I hope we see "Vipersan" back on the forum, his posts were always good for helpful info and his improvisations with stuff was inspirational.
We could do with him back in the C-Band section.

 

[zorrin]

Of course it will work.

How long it stays up there is another question.

Here is the formula to calulate the wind loading of a mesh dish (add 50% to the final figure for a solid prime focus and 60% for an offset that is non inverted)

XRT-C | Wind Loading Calculations with a Radio Telescope

www.xrt-c.co.uk

OK and empirically?
What do you think personally?
Or would you rather do it or not?
If you are not French of course...

I prefer your experience, there are too many factors.

 

[Channel Hopper]

Factors are always going to be local issues, which includes your faulty calculator.

Your hardware looks strong enough, though if the Alcoa is built to use a 3.5" post , then you should be looking for a pole of 89mm outside diameter.

 

[zorrin]

Factors are always going to be local issues, which includes your faulty calculator.

Your hardware looks strong enough, though if the Alcoa is built to use a 3.5" post , then you should be looking for a pole of 89mm outside diameter.

Thank you so much @Channel Hopper
I tested putting the polar mount on an 80mm tube and it seemed to be perfectly positioned.
At the same time with the 3mm thickness of the 76mm diameter tube and the 2mm thickness of the 80mm tube should compensate for the missing 9mm to reach 89mm...

Well it's not great, I'll try only in 1m80 and see how long it will stays up

 

[Channel Hopper]

That should do, try to get the additional sections down to the stabilising 'fins', and then tack weld them (saves drilling through at two points to stop twisting), or slot accordingly to sleeve over to a lower point.

If the Alcoa instructions for the polarmount cover the extended panels there should be no reason why your pole upgrades cannot work with the larger diameter reflector, the weakest point once you go up a size will always be the actuator pivot points.

 

[zorrin]

That should do, try to get the additional sections down to the stabilising 'fins', and then tack weld them (saves drilling through at two points to stop twisting), or slot accordingly to sleeve over to a lower point.

If the Alcoa instructions for the polarmount cover the extended panels there should be no reason why your pole upgrades cannot work with the larger diameter reflector, the weakest point once you go up a size will always be the actuator pivot points.

I have the idea to take a tube of 80 mm over a meter long.
Cut it in all the length.
From the bottom to 50cm make 4 notches for the passage of the 4 reinforcements.
And find a solution to be sure it wil not twist anyway.