LNB from basement

Thread Starter

bootloader9800

Joined Jan 12, 2021
27
Hello all and hope everything is fine with you all!

So I have been doing some review/ learning about antennas. I found this, what I think is a, low-noise block downconverter (LNB) in the basement. (The roofers removed it when I got a new roof a while ago).

1.jpg

The picture above, pic # 1 shows the LNB. What is the purpose of the white caps/lids?



2.jpg

In pic # 2, Why does the LNB on the left have those “steps” looking formations but the LNB on the right does not?



3.jpg

In pic # 3 above, what are the 2 items shown with the green and orange arrows? Why are the white tabs 90 degrees off compared to the LNB on the left versus the LNB on the right? ( The orange arrow is pointing to a yellow plastic tab thing that can be broken with half a newton of force. You can see a better view of that yellow tab in pic # 6 below. )



4.jpg

In pic # 4 above, why do you think the body is long and doesn’t have those “Steps” like in pic # 2 above?



5.jpg

In pic # 5 above, why doesn’t the inside of the waveguide have “steps” similar to pic # 3 above? Why is the inside "oval" ?



6.jpeg

In pic # 6 above, in the center top part of the pic, you can see where the LNB from pic # 4 used to sit. Does the radius of those 3 holes mean something? Why did the designer pick holes of that exact size?

Thank you for the replies!
 

andrewmm

Joined Feb 25, 2011
1,497
Hello all and hope everything is fine with you all!

So I have been doing some review/ learning about antennas. I found this, what I think is a, low-noise block downconverter (LNB) in the basement. (The roofers removed it when I got a new roof a while ago).

View attachment 240625

The picture above, pic # 1 shows the LNB. What is the purpose of the white caps/lids?



View attachment 240626

In pic # 2, Why does the LNB on the left have those “steps” looking formations but the LNB on the right does not?



View attachment 240627

In pic # 3 above, what are the 2 items shown with the green and orange arrows? Why are the white tabs 90 degrees off compared to the LNB on the left versus the LNB on the right? ( The orange arrow is pointing to a yellow plastic tab thing that can be broken with half a newton of force. You can see a better view of that yellow tab in pic # 6 below. )



View attachment 240628

In pic # 4 above, why do you think the body is long and doesn’t have those “Steps” like in pic # 2 above?



View attachment 240629

In pic # 5 above, why doesn’t the inside of the waveguide have “steps” similar to pic # 3 above? Why is the inside "oval" ?



View attachment 240630

In pic # 6 above, in the center top part of the pic, you can see where the LNB from pic # 4 used to sit. Does the radius of those 3 holes mean something? Why did the designer pick holes of that exact size?

Thank you for the replies!

The picture above, pic # 1 shows the LNB. What is the purpose of the white caps/lids?
A) To keep "crap" out of the metal work

In pic # 2, Why does the LNB on the left have those “steps” looking formations but the LNB on the right does not?
A) steps are probaly a rf impedance match, to do with the rings inside


Pic #3, I would guess is a left or right hand polarisation shift action ( a mechanical switch in RF terms )


hole size etc

you need to look up wave guide and horn antenna design techniques
 

Yaakov

Joined Jan 27, 2019
3,190
The plastic caps are radomes which are transparent to radio frequencies but protect the antenna.

The feed horn with the rings is called a scalar horn. The purpose of the rings is to reflect the signals coming at sharp angles from the edges of the dish which are poor quality, and on a dish like that one not even the intended focus of the horn.
 

anniel747

Joined Oct 18, 2020
825
The plastic caps are radomes which are transparent to radio frequencies but protect the antenna.

The feed horn with the rings is called a scalar horn. The purpose of the rings is to reflect the signals coming at sharp angles from the edges of the dish which are poor quality, and on a dish like that one not even the intended focus of the horn.
Good explanation.
 

sparky 1

Joined Nov 3, 2018
544
https://www.amazon.com/KaKu-Slimlin...6E89F62/ref=dp_fod_2?pd_rd_i=B006E89F62&psc=1

Some of the mathematics related to wireless communication can be many years from the antenna technology.
An example: Bell systems Journal by CE Shannon 73 years ago preceeded Bell labs Telstar 1 1964 and the improvement since.

There are many other mathematical representations for communication that helped shape the technology.
 
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Thread Starter

bootloader9800

Joined Jan 12, 2021
27
Frequency is the main reason for selecting dimensions of a feedhorn.
Ty. Can you please recommend a textbook that teaches about designing a feedhorn. Also, I dont see the active element in these LNBs that is supposed to actually receive the signal. Is the active element some where in the pictures and I missed it? Ty
 

Thread Starter

bootloader9800

Joined Jan 12, 2021
27
Ty all for the replies! This is the OP.
I dont see the active element in these LNBs that is supposed to actually receive the signal. It probably looks like a small piece of straight wire that is an inch long. Is the active element some where in the pictures and I missed it? Can you please point to it the pictures? Ty
 

anniel747

Joined Oct 18, 2020
825
Ty all for the replies! This is the OP.
I dont see the active element in these LNBs that is supposed to actually receive the signal. It probably looks like a small piece of straight wire that is an inch long. Is the active element some where in the pictures and I missed it? Can you please point to it the pictures? Ty
Ok, by active element you mean the receiving "wire"? It may not be visible and can be a strip-line on the opposite side of a PCB for ingress protection.
 
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