How Do Scalar Rings Work

[Pixl]

I understand the scalar rings adjust what the lnb "sees" from the dish. But I would like to read up on the technology as to how they do this. I've searched all over Google, just not coming up with the right key words to find a detailed report on their design.

Jim

 

[richyrich]

I understand the scalar rings adjust what the lnb "sees" from the dish. But I would like to read up on the technology as to how they do this. I've searched all over Google, just not coming up with the right key words to find a detailed report on their design.

Jim

Scalar rings are under "image rejection" when it comes to satellite signal reception. When the wave, (which looks to the dish like a "s" or "z"), enters the focal point of the feed, the satellite you want signals should be the "S" or "Z" wave only located on the inside of the feedhorns round middle part, which is its' waveguide. The scalar rings reject any other satellites, or any other signal, of the same wavelength, or larger wavelength (which in satellite signal terms is lower or high in freq.) reflected from the middle of the dish, by absorbing and intercepting these "larger" waves, not allowing them to enter the middle of the feedhorn where the wanted signals are. That is about all I can say about the "scalar" rings mounted on a feedhorn. These other rejected signals can be point-to-point towers on the same, or lower frequencies, that carry communications to different areas; or it can be an adjacent satellite signal not rejected by the dish itself, which if it does not have its' main lobe of signal within 2 degrees of the wanted satellite, does pick up signal from the adjacent one. This has to do with both the dishes design (F/D), and its size (say 7 campared to 10 feet in diameter) which gives the dish its beamwidth, the amount the main lobe of the dish picks up in degrees of width, like 2 or 3 or 4 degrees, depending on its size and design of F/D. : you are! i am...

 

[B.J.]

My understanding (or actually more of a non-scientific intuitive guess) is along a slightly different line. While I'm sure the rings have function relative to reducing TI signals coming from off the edges of the dish, I think that they also function to increase the efficiency of the outside portions of the dish for the desired signals. Signals hitting close to the middle of the dish (talking prime focus here) go into the throat of the feedhorn at a pretty direct angle, and don't have any problem, but signals coming from the edges of the dish, particularly of a low F/D dish, come in at a rather extreme angle, so that the cross section of the throat opening gets pretty small. For low F/D dishes, the outside of the dish isn't very efficient.
My thinking is that the scalar rings both help to guide that signal into the throat and they actually increase the gain of signals from the outside of the dish much like the directors of a YAGI antenna. I think the guiding effect is related to the fact that RF can bend around corners when they approach a sharp object that blocks it's path. For example, you can receive radio signals at frequencies that are normally line of sight only when you are blocked by a solid surface because when the waves reach the edge of the blocking solid, they re-radiate in all directions. I think the effect related to the directors on a YAGI antenna is that the directors get hit by the waves that might otherwise miss the driven element, or throat in this case, and re-radiate, increasing the signal that comes from the direction that the directors are aimed, ie the edges of the dish, while rejecting, or acting as reflectors for signals coming from other directions. The spacing is critical if the re-radiation is to be continued on by the next director.
Anyway, I'm not confident that my understanding is anywhere close to correct, however that's what came to mind when I looked at scalar rings, and it seems logical to me.

 

[Pixl]

It sounds like both of you are close to the answer. The training I had in waveguide theory (long time ago) tells me the ribs of the rings act as 1/4 wave shorting stubs canceling out unwanted signal. But how any of these ideas work with the ring PAST the opening to the lnb I don't get.

 

[1ADAM12]

Also noise cancellation

It sounds like both of you are close to the answer. The training I had in waveguide theory (long time ago) tells me the ribs of the rings act as 1/4 wave shorting stubs canceling out unwanted signal. But how any of these ideas work with the ring PAST the opening to the lnb I don't get.

Yes, You all make a good explaination of the Scalar ring. In addition it seems to reduce radiant noise from around the edge of the dish and improves signal to noise ratio.

In the case of the stacked cone Scalar its tunning is so sharp that it can discriminate between tp's.

 

[AcWxRadar]

Tantalus,

I believe that both Rich and B.J. are quite on track with their explanations.

I am no engineer in this regard, but I have my own comprehension of the theory.

B.J. mentioned the term "re-radiating" and I think that this is a key factor.

Depending upon the number of rings and the distance of the spacing of the rings, I believe that the scalar ring assembly amplifies the signals which are arriving from the one specific satellite that is the most perfectly in line with a perpendicular beam to the center of an imaginary plane of the dish reflector.

Signals from that satellite which strike the outer areas of the dish, where it might be less efficient for amplification, are reflected back to the dish by the scalar rings and refocused and concentrated better towards the throat of the waveguide of the LNBF or feedhorn.

Only the signals that are perfectly incident to the dish reflector are reradiated back perfectly and any signals from satellites off to the side of the desired and intended satellite are scattered away from the feedhorn and therefore rejected, which aids the intended signal by reducing interference.

The desired satellite signals are reflected (re-radiated) back and forth between the scalar rings and the dish reflector until they are best focused at the feedhorn and waveguide. If the design of the scalar ring is a good match for the signal's frequency (spacing of the rings is a specific and appropriate multiple of the wavelength of the frequency) and the scalar ring assembly is positioned at the appropriate distance from dish reflector and matched to the reflector's F/D ratio, the otherwise weak signals will be amplified suffiiciently for the receiver to lock on to that signal and provide a more stable signal quality.

There are stepped or conical scalar rings and flat scalar rings and I think that the difference between these styles of construction make the scalar ring's application more effective for the specific geometry of the dish reflector you are using.

I am not sure that my explanation is completely accurate, but I belive that it is a fair analogy for a layman's explanation.

RADAR

 

[Pixl]

Wow AC, that was intense. So to put in plain words you are saying it catches signal that got past the lnb horn, and recycles it to come back a second or more times?

 

[richyrich]

scalar network

In satellite antenna theory, the perfect satellite dish fits the frequency it is receiving. That is, it's F/D ratio makes a 4th dimensional perfect match to the satellite signals shape.

Take for instance, a listening device. Sound is amplified in front of it with a feed of a microphone, and it is located close to the reflector (a mini dish), which has a very deep shape, which gives it a low F/D. This is because sound, as a frequency, is found very low in frequency, and is kind of round, that is, it eminates from a small point (your voice box opening), to a larger round area (your mouth), and also gets bigger from there.

These functions of round waves make it actually the only true three dimensional wave (where terrestrial tv waves, am, fm, are more pointed in a certain direction, and go from "up" to "down" and are two dimensional, or flat) are only true in satellite signals and somewhat in a CB's signal, because they go all the way around the antenna used to propagate, and "circle", and radar does the same, only it uses a directional circulation.

So, a deeper dish is better at lower frequencies, like C compared to KU, and the scalar makes up for the dish which does not fit the three dimensional shape of the wave it is receiving. Which is why on a deep dish, you put the throat farther out from the scalar (according to Hoyle), and it's F/D is lower, and the wave propogates to a shorter distance than a flatter dish with a higher F/D. From here, one can actually show that it is focal point, that is, where the feeds throat sits, that causes the signal to enter correctly, (or wrongly and everybody here said something right about "the scalar rings". But what I did not say was why something should sound wrong about what I said here and left out here. Maybe another day...:up

 

[whatchel1]

Out of phase

It sounds like both of you are close to the answer. The training I had in waveguide theory (long time ago) tells me the ribs of the rings act as 1/4 wave shorting stubs canceling out unwanted signal. But how any of these ideas work with the ring PAST the opening to the lnb I don't get.

They primarily reduce out of phase signals by bouncing those back to surface and thus at these wave lengths get broken up. Thus the standing waves are broken up. When the stand waves are reduced what is left is the primary wave and so a form of amplification by only receiving the waves that are timed to reinforce the signal. The conical scalars are designed for offset dishes and direct them from the multiple lengths of the offset to also increase and amplify the signals. There is some rejection of the waves that are coming from off axis sources.

 

[Hermitman]

Here's a couple of url's that might be useful. These pages concern the design of a SETI antenna scalar ring and feedhorn but the theory is the same. The first one has general information and concepts. The other is a xls spreadsheet for designing a feedhorn and scalar ring. Be advised, the term choke is just another name for scalar ring. If you really want to get into the calculus formulas of designing a scalar ring, google "thesis conical scalar ring". The folks in New Zealand and Austrailia has some rather complex and detailed papers on this. Have fun.

Care and Feeding of a SETI Dish

http://www.setileague.org/software/feedhorn.xls

 

[Pixl]

Here's a couple of url's that might be useful. These pages concern the design of a SETI antenna scalar ring and feedhorn but the theory is the same. The first one has general information and concepts. The other is a xls spreadsheet for designing a feedhorn and scalar ring. Be advised, the term choke is just another name for scalar ring. If you really want to get into the calculus formulas of designing a scalar ring, google "thesis conical scalar ring". The folks in New Zealand and Austrailia has some rather complex and detailed papers on this. Have fun.

Care and Feeding of a SETI Dish

http://www.setileague.org/software/feedhorn.xls

Thanks Herm, I see I have a lot to read up with the links you provided. Also thanks to the other replies you guys posted, I'm starting to get the idea how this works.

Jim

 

[AcWxRadar]

Wow AC, that was intense. So to put in plain words you are saying it catches signal that got past the lnb horn, and recycles it to come back a second or more times?

Yes, without going into the nitty gritty engineering theories and specifications, that pretty well sums up what the scalar ring is doing. Trying to focus the weak signals into a one shot "stronger beam" for the LNB to use by reflecting the signal back and forth between the dish and the scalar ring until you achieve the best concentration of the signal.

Quite similar to what reflecting telescopes do with light - bounce the dim light from a far away star back and forth between mirrors to focus the light waves into a more concentrated point that you can view clearly.

RADAR

 

[richyrich]

Since the SETI dishes reflect light (or "freq."); one would think the people of the solar world have won now. They have used the big C Band dish just to make hot water, covering it in a heat reflecting material back to the feedhorn area, and have the dish follow the sun by directing it to the sun (and elevating, dual motor style) when they need hot water. To me, this is as much a waste of money as having all the channels and only watching ESPN; and then some, as a dish is worth more for my use as a channel monster any way I set them up. One wonders what else a big dish will or can do somebody has not thought of yet comes to mind. If it receives better, as system antenna, let us know how much hot water is worth more in savings, as if hot water costs 500-1000 a year, the system pays for itself in 5 years! Then put them both up, and you have 3 dishes in your back yard, and they each do a different thing!

 

[Babadem]

Quite an interesting read!