Scalar rings

[mister_dk]

I have had a BUD for several years. I know that the old feedhorn and lnb had a plate that had scaler rings on it. I have never been able to find a clear definition or explanation of what scaler rings are.

What function do scaler rings perform?
Are they necessary for both C and KU when using a BUD?
Why don't smaller KU dishes require the use of scaler rings?
Do conical scaler rings function the same as regular scaler rings?
What do conical scaler rings do that is different than plain flat scaler rings?

 

[Anole]

good questions:

What function do scaler rings perform?

Simply put, they limit the view of the LNB through the feedhorn, to just the surface area of the dish.

Are they necessary for both C and KU when using a BUD?

Well, the big scalar you see on the BUD, is for C-band.
On the LNBF's, the Ku scalar is built in.
Not sure how that is handled on a dual band Chaparral feedhorn, for instance.

Why don't smaller KU dishes require the use of scaler rings?

The scalar is built into the LNBF.

Do conical scaler rings function the same as regular scaler rings?

Yes, absolutely.
But, the conical scalar is for a dish with a higher F/D ratio (longer focal length).
As a common rule, offset dishes have an F/D in the .6 to .7 range.
The prime feed (center feed) dishes have an F/D in the .3 to .4 range.

What do conical scaler rings do that is different than plain flat scaler rings?

They simply have smaller field of view.
For looking at a little slice of the parabola, that is farther away.

You could compare the flat scalar to a camera with a wide angle lens.
Light (picture) from far left and right of the lens is admitted.
The conical scalar is like a camera with a telephoto lens.
The latter has a smaller field of view.

 

[mister_dk]

Thanks Anole for taking the time to explain this to me. The explanation is very direct and understandable. It's great to know that there are people out there that are so quick and willing to help educate others.

Thanks again.

 

[Natedawg63]

I have spent several hours reading at this site... Very well put together, and easy enough for a newbie like me to grasp... I use it as a go-to when I have a question about something I do not quite grasp. Has some good links also

Footprints by Dish Size - Adjusting the Polar Mount for Prime Focus Antenna - C/Ku-Band Satellite Systems - Tuning, Tracking, Azimuth, Elevation, Declination Angles, F/D Ratio, Focal Distance, Inclinometer, LNB/Feedhorn Assembly, Actuator Assembly, C

Nate

 

[spirals]

Design Information for scalar rings choke plates please.

I am looking for information on the design of C-band scalar ring choke plate assembly. I have tried searching with Google and have turned up nothing in the way of a calculator or paper on the theory.. I am designing a Cassegrain fed dish with a high value f/D that is outside the range quoted for the Chaparral Corotor II+ WB (0.35 to 0.45) my case is more like 0.72. I also have conflicting information if the standard unit has three rings or a three ring spiral on standard plates. Any suggestions, web site or other source for design information. Thanks in advance guys.

 

[Hermitman]

For that range of f/D, you're looking at a conical scalar ring. Have you tried searching for something like " thesis conical scalar"? Also, if you realy want the best performance, look at conical corrugated feedhorns. Try searching for "thesis conical corrugated feedhorn". There are several universities in the New Zealand and Austrailia region that have had good work done in these areas. These papers are highly detailed in calculations and formulas, and can be pretty dry at times but should give you enough to get started. Good luck.

 

[Anole]

Q: Why don't smaller KU dishes require the use of scaler rings?

A: The scalar is built into the LNBF.

See pictures below.
The Ku LNBF on the left has a circular scalar for a round dish.
The LNBF on the right has an elliptical scalar for an elliptical dish.
As you can see, they look identical from the outside.

These pix came from an Australian satellite forum.
Apparently, they run into such things over there.
(Possibly from some direct-to-home service in Oz)
I'm not aware of any such LNBFs with elliptical scalars in North American service.