Home made 90cm Ku band dish

[Biswajit.HD]

Very innovative indeed.... good work... keep hunting satellites :tup

 

[jkaza]

good Job... :k :tup

 

[AsitPaul]

Innovative.
Keep trying and informing us dear.

 

[srinivas33]

Thank you friends for your support. Mounting is my idea, dish idea is from VK4BKP. Search this "satellite dish construction plywood vk4bkp" in Google.

 

[srinivas33]

but very low signal of insat 4b, we can easy found insat 4b and good signal in 60cm dish then your dish 90cm

Yes you are right, but this is hand made, I'm experimenting so will try different approaches and make corrections of my mistakes and improve it. Final aim is making a affordable high gain big dish for those who have less income.

 

[srinivas33]

Great..... Can you try C band LNB. I planed a 100 CM dish as like you. You try C band LNB and reply me. 83* is so many FTA channels.

Hi Moloybora,

I have done experiments with my home made dish, the strongest C band signal available is ST2 satellite @88 deg East, Its signal can be received by a 90 cms dish(see its footprint in satbeams.com), i experimented and got the quality upto 40% and goes to zero in next second it keeps on and off. So i cannot lock into it.

So i suggest you to try making a larger diameter dish about 5 ft or 6ft for Insat 4a, etc. using the following idea.

see its part2 also,

you will get an idea of how to make the mount for the dish and also the dish can be disassembled, you can try it with flat aluminum or flat iron rods and bend them and make two holes at hub and tighten it at hub with two nuts and bolts for every rib.

I'm now suffering because my first dish is short of diameter. I will inform after i complete mine, you too make it.

 

[MOLOYBORA]

Dear Srinivas
Presently I am not making the dish. What channel you will get from 88*. C band LNB (13K) is not available in our location. Is it purchase from Online? What is the meaning fd 0.4

 

[srinivas33]

Dear Srinivas
Presently I am not making the dish. What channel you will get from 88*. C band LNB (13K) is not available in our location. Is it purchase from Online? What is the meaning fd 0.4

C band channels in Satellite ST2 at 88 deg East

Transponder Frequency polarity Symbol Rate Channel Name Encryption

3629 H 24700 TVBS FTA
3671 H 9256 Buddha
compassion FTA
TV Station
Life TV FTA
Sinda TV FTA

source: ST 2 at 88.0°E - LyngSat


Me too couldn't find 13k lnbf, i found this on ebay but shipping price is high

C Band ESX241 Satellite Dish LNB LNBF Single Output 13K | eBay

in shop clues: a clone of 13 k lnbf i think, has poor rating, not good i think,

Universal 13 degree C-Band Dual Pol. LNB with Single Output

I'm planning to use the 17 k c band lnb, but will use large dish(6ft) then no need of 13k.

What is F/D?

here F is focal point distance from the origin of the parabola, and D is the diameter of the dish.

For example if a parabola has focus at a distance of 63 cm,
and diameter of the dish is 160 cm,

then divide F with D then we get 63/160 = 0.39

this ratio is F/D.

Now why F/D ratio is near to 0.4 for C band and 0.6 and 0.7 for ku band dish?

this is because of scalar ring, if we push the lnb into the scalar ring towards the dish it illuminates larger diameter dish, if we pull away the lnb from scalar ring it illuminates less diameter dish. If we have a ku band dish and we put a c band lnb, we will have no space to pull it back from scalar ring, it will reach the tip or it still needs to pull back to illuminate the ku band dish perfectly.

if we push the lnb deep into scalar ring for a ku dish then it will have
wide illumination and it also receives the radiation from the earth below, this degrades the our intended signal.

I have an excel calculator for how much we should push the lnb into a scalar ring based on f/d ratio. I will post the formula from it now.

Formula for how many inches to push the lnbf into the scalar ring

in inches = -10*(F/D ratio)+4.32

Now for example i made a dish with F/D = 0.7

now distance in inches = -10*(0.7)+4.32
= -2.68 inches

If you get negative value here means you should bring it from back outside of the scalar ring but you will have no space left so you cannot screw the lnb there as it will be out of scalar ring.

So for C band lnb you should use a dish with f/d of 0.38 to 0.42 and nearer. So that you will not get negative value above.

reference

Designing Paraboloids @ The Microwave Museum


How to construct feed horn based on F/D ratio

http://www.packratvhf.com/Article_9/Dish_Not.pdf

 

[srinivas33]

1. What type of feed horn to be used for different f/d ratios?

and what is f/d?

 

[jkaza]

Thanks srinivas33 for nice info. :k
:huh