What is a scalar ring and what exactly does it do?

[Pepper]

I asked the entire question in the thread title.

Once there's an answer to this maybe it should be in the FAQ.

 

[qwert1515]

A scalar ring is the ring you see around C-Band LNBs, because the focal distance (Size of dish vs. the LNBs distance away from the dish) for dishes is different the scaler ring is used to adjust how much of the dish the LNB will see. If the LNB sees more area than the dish it will pick up additional noise, if it sees less area than the dish it is like having a smaller dish.

 

[Pepper]

I don't really understand that at all. In all the pictures I've seen the scalar ring is outside of the "tube" and at or behind the opening, so how could it possibly affect signal bouncing from the dish face into the tube?

Pictures or diagrams illustrating the effect would be nice.

 

[trinidex]

I was about to say that was a very succint explanation, I have never heard it put that way before...but then I read Pepper's post.

 

[Pepper]

Not only that, I just noticed I used "affect" and "effect" correctly! But still have no idea what the thing actually does.

 

[Lak7]

It's like Blinders on a Horse.

 

[Mauiguy]

I don't really understand that at all. In all the pictures I've seen the scalar ring is outside of the "tube" and at or behind the opening, so how could it possibly affect signal bouncing from the dish face into the tube?

Pictures or diagrams illustrating the effect would be nice.

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

If you go to : F/D Setting/Scalar Adjustment

on that site, you will find diagrams, and some explatations.

 

[satcom1]

Interesting,according to that link they are noise interference rings. They look like they are in the realm of waveguide and microwave cavity magic. I take it that they function as unwanted radiation QRM eliminators.

 

[tvropro]

In all feedhorns the scaler rings reject thermal noise (kelvin), TI, etc from beyond the edges of the dish. Also normal feedhorns such as (Chaparral) the scaler rings act as a choke plate to cut off noise and out of focus energy being picked up by the feedhorn throat. In a dual mode hybrid feed (ADL) the moding chambers take this out of focus energy, puts it back in phase to be used as good signal. This is why a properly set up ADL (dual mode hybrid feed) such as a RP1-C will out perform a Chaparral.

 

[Smith P.]

"The most common type of feedhorn manufactured today is called a scalar feedhorn. This type of feed has a large circular plate with a series of three or four concentric rings attached to its surface. The scalar rings conduct the incoming signal from the outer edges of the focal cloud to the large waveguide opening located at feed center. The scalar feedhorn primarily sees or illuminates the inner portion of the antenna's surface area, while attenuating the signal contribution from the outer portion of the dish by 8 to 22 dB, depending on whether the dish is deep or shallow in its construction.

Molecular motion within the Earth itself generates random noise which permeates the entire electromagnetic spectrum used for the transmission of satellite signals. This random noise is many times stronger than the satellite signals reaching any location. The attenuation or illumination taper provided by the feed sharply reduces the reception of the Earth noise which lies just beyond the antenna's rim. The outer area of the antenna's surface therefore acts more as an Earth shield for the feedhorn than as a contributor to the overall signal gain of the receiving antenna."

 

[satcom1]

Last week I was on I-55 going through West Memphis and I saw a large Commercial C-Band TVRO in a horizon to horizon sweep and vertically truncated design. It also has a matching "waveguide" slotted aperature for the LNB. Anyone have information about this design?

 

[sideswiper]

very good read thanx guyz

 

[Pepper]

I tried running all that stuff through the google greek-to-english translator but it didn't help.

I am learning, slowly.