My setup

[quickboy]

well QB we can still concider this above dish as whole parabola , while its shape is not in oval shape , ? what you say ? while the prime focal lenth will be different

Keep four of them together so they touch each other and see if the outline makes a parabola, of course you may need to fill in the gaps, I have seen pictures of some guy actually welding together some offset dishes of similar size and making a prime focus dish to receive c-band

 

[vishvish]

well QB we can still concider this above dish as whole parabola , while its shape is not in oval shape , ? what you say ? while the prime focal lenth will be different

Keep four of them together so they touch each other and see if the outline makes a parabola, of course you may need to fill in the gaps, I have seen pictures of some guy actually welding together some offset dishes of similar size and making a prime focus dish to receive c-band

well i agree with your view , but what i want to say is , this above dish by vikram , looks as perfect parabola perfect circle rather then ovel ( like offset normal dish )

here it is the depth of the dish is small , so the prime focus will be large , assume the JAMS dish looks like the same less depth

look here , well i agree that the feed comes into axis so less signal than offset dish but dosent effect on large prime dish's ,

, i just arguing the theory , but in practical the dish size is less , so prime focus is not good

 

[quickboy]

well QB we can still concider this above dish as whole parabola , while its shape is not in oval shape , ? what you say ? while the prime focal lenth will be different

Keep four of them together so they touch each other and see if the outline makes a parabola, of course you may need to fill in the gaps, I have seen pictures of some guy actually welding together some offset dishes of similar size and making a prime focus dish to receive c-band

well i agree with your view , but what i want to say is , this above dish by vikram , looks as perfect parabola perfect circle rather then ovel ( like offset normal dish )

here it is the depth of the dish is small , so the prime focus will be large , assume the JAMS dish looks like the same less depth

look here , well i agree that the feed comes into axis so less signal than offset dish but dosent effect on large prime dish's ,

, i just arguing the theory , but in practical the dish size is less , so prime focus is not good

@vishwa,

It does not look circular on perimeter, Also think about the length of the focus, A four feet dish with three feet focal length, Does this look practical, and what is the f/d? 90/10=9, well the best c-band feeds i have seen is capable of 0.42 to 0.25, so make a feed capable of f/d =9? HOW?

 

[quickboy]

This is my old shyam C band dish , When first time launched Doordarshan in india. Tv is Very costly @ this time and few houses.

THat looks a real stunner, where is the base ?

Did it come with an AZ/EL mount or polar ?

 

[vishvish]

for the above dish given f/d, some calculations , i agree

f/D = 7.50
Focal Length = 9000.00 mm.
Illumination angle for feed = 7.6 degrees
Space attenuation = 0.01 dB
Desired taper = 9.99 db for 10 dB edge illumination
A simple feed horn would have a diameter of 15.77 wavelengths for a 3 dB beamwidth of 4.18 degrees
Gain at 50% efficiency = 31.02 dBi

 

[quickboy]

for the above dish given f/d, some calculations , i agree

A simple feed horn would have a diameter of 15.77 wavelengths for a 3 dB beamwidth of 4.18 degrees
Gain at 50% efficiency = 31.02 dBi

A good project, Best of luck,

 

[vishvish]

for the above dish given f/d, some calculations , i agree

A simple feed horn would have a diameter of 15.77 wavelengths for a 3 dB beamwidth of 4.18 degrees
Gain at 50% efficiency = 31.02 dBi

A good project, Best of luck,

cool bro , i think you are questioning feedhorn daiameter?

 

[quickboy]

cool bro , i think you are questioning feedhorn daiameter?

Nope, I was thinking where to get one machined and at what cost ? :blush:

 

[vishvish]

simply means it dosent work for c band

 

[Vikram]

Qb and vishvish Please Tell me after calculation what is the Focal leanth Of my dish,
Also suggestion me which is better Focal length or prime focus