Dual and Quad Multi-Focus Scalar Rings

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Dual and Quad Multi-Focus Scalar Rings

Post by tek2000 » Thu Jan 29, 2015 6:20 am

We now have dual and quad multi-focus scalar rings in stock! You can purchase them from our webstore or through Amazon.com

Possible applications include reception from up to 4 adjacent satellites using a single stationary dish (e.g. 121W, 125W, 127W, 131W) or reception of both linear and circular satellite signals on a motorized dish by installing two different LNBFs(e.g. Linear LNBF and Circular LNBF). This is an excellent way to receive sat 40.5W by using a circular lnbf.

Depending on your dish size, here is how close adjacent satellites need to be for optimum reception:

240cm dish: ~3.0 degrees apart
300cm dish: ~2.3 degrees apart
350cm dish: ~2.0 degrees apart
400cm dish: ~1.8 degrees apart

Notice that a 350cm dish is ideal for this application, although the 300cm and 400cm work very well too. If you own a 240cm dish, try receiving satellites that are 4 degrees apart.

Other possible applications include simultaneous reception of C-band and Ku-band signals with negligible signal attenuation by separating the bands.

The quad scalar ring will allow you to receive every type of satellite signal:FTA C-band (North America), FTA C-band (Latin America), FTA Ku-band, Dish, DirecTV, Bell, Claro, etc.

NOTE 1: LNBs are sold separately.

NOTE 2: The dual scalar ring attached to 3 LNB support rods while the quad scalar ring attaches to 4 LNB support rods. You may have to retrofit your support rods equidistant around the dish rim in such a way that the scalar ring axis is aligned with the satellite arc (Clarke Belt) for optimum reception.

NOTE 3: Recommended for 240cm, 300cm, 350cm and 400cm mesh dishes.
scalar_quad_0.JPG
scalar_quad_1.JPG
scalar_quad_2.JPG
scalar_quad_3.JPG
scalar_quad_4.JPG
scalar_quad_5.JPG
scalar_quad_6.JPG
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Re: Dual and Quad Multi-Focus Scalar Rings

Post by tek2000 » Thu Jan 29, 2015 11:05 pm

Here is the dual focus scalar ring:
scalar_dual_0.JPG
scalar_dual_1.JPG
scalar_dual_2.JPG
scalar_dual_3.JPG
scalar_dual_4.JPG
scalar_dual_5.JPG
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Re: Dual and Quad Multi-Focus Scalar Rings

Post by tek2000 » Thu Jan 29, 2015 11:17 pm

Here is some background information on multi-focus feeds from the Professor's Guide to C-Band (Tek2000 contributed extensively to this section).

http://www.tvrosat.com/phpBB-3.0/phpBB3 ... 146&t=1252


8.5: Multi-Focus and Off-Axis Feeds

In high school you were probably taught that a parabola has only a single focus and that incoming rays parallel to the parabola axis will converge to this focus. When it comes to parabolic reflectors this is only partly true because there are in fact many convergent points! The prime focus will always have the greatest gain, but the other off-axis foci will also have substantial gain and can be used for reliable reception. The reason there are multiple foci is because total radio wave amplitude at any point is derived by adding the sum total of all reflected waves. At the prime focus, all waves will be in phase and the sum will be maximum, but at other points, they will be only slightly out of phase and still add constructively.

Lets consider a simple example where two radio waves of amplitude A are reflected to the prime focus:

Prime Focus Wave = A*cos(ft) + A*cos(ft) = 2A*cos(ft)

Thus the amplitude is double at the prime focus.

Now consider what happens when these waves are added at an off-axis point where they are slightly out of phase:

Off-Axis Wave = A*cos(ft) + A*cos(ft + phase_error)

Expanding the second cosine function:

Off-Axis Wave = A*cos(ft) + A*cos(ft)*cos(phase_error) - A*sin(ft)*sin(phase_error)

If the phase_error is very small, for example 1-2 degrees, then cos(phase_error) ~ 1 and sin(phase_error) ~ 0. Therefore,

Off-Axis Wave ~ 2A*cos(ft)

Thus we see that an off-axis feed will have almost as much gain as a prime focus feed and is a useful thing to know. You can verify all this by installing a 2nd LNBF beside your prime-focus LNBF (see picture below).

A practical application of all this is to receive multiple satellites simultaneously. For example, if your dish prime focus is pointed at 101W, an adjacent LNBF could be positioned to receive 103W, while another LNBF on the other side of the prime focus could receive 99W!

An important formula to keep in mind is the off-axis length for positioning the adjacent LNBFs. This is approximately given by:

Off-Axis Length = Focal Length x tan (1.1*Angle)

For example, with a 12ft mesh dish and focal length of 51 inches, if you wanted a 2 degree separation (most satellites are separated by 2 degrees):

Off-Axis Length = 51 x tan (1.1*2) = ~2 inches

Thus if you separate your LNBFs by about 2 inches, you will be able to receive all adjacent satellites simultaneously.

This works very well with a 12ft dish where it is possible to separate the LNBFs by 2 inches. Most C band LNBFs are about 2 inches in diameter and so it becomes impossible to implement shorter distances unless the LNBF circular waveguide structure is modified. With 10ft and 8ft diameter dishes, the off-axis distance are smaller than 2 inches and so 2 degree separation is not possible with commercial LNBFs that are 2 inches in diameter. However, it has been found experimentally that 2 degrees of separation is possible with a 12 ft dish, 3 degrees of separation for a 10ft dish and 4 degrees of separation for an 8ft dish!

Finally, it is worth mentioning that the off-axis feeds need to be on the axis that is parallel to the satellite arc in order for this to work (see pictures below).

What is the point of all this? Since off-axis feeds suffer very little attenuation, they can be used for circular polarization reception and Ku band reception while prime focus is reserved for linear C band reception only. This has the advantage of separating the bands and polarities and not compromising on signal reception. Another example might involve using a stationary 12 ft dish to receive multiple satellites simultaneously without an actuator. For example, it has been experimentally verified that a 12 ft dish with prime focus pointed at 127W can simultaneously receive 121W, 123W, 125W on one side and 131W, 133W and 135W on the other side of the prime focus!

If this has you all excited and you have the mechanical inclination and physical room on your property, you might consider setting up your own satellite farm with only 4 stationary 12 ft antennas to simultaneously receive the whole arc:

Stationary 12ft Dish 1
Off-Axis 4 = 37.5W
Off-Axis 3 = 40.5W
Off-Axis 2 = 43.1W
Off-Axis 1 = 45W
Prime Focus = 47.5W
Off-Axis 1 = 50W
Off-Axis 2 = 55.5W
Off-Axis 3 = 58W

Stationary 12ft Dish 2
Off-Axis 4 = 83W
Off-Axis 3 = 85W
Off-Axis 2 = 87W
Off-Axis 1 = 89W
Prime Focus = 91W
Off-Axis 1 = 95W
Off-Axis 2 = 97W
Off-Axis 3 = 99W
Off-Axis 4 = 99W


Stationary 12ft Dish 3
Off-Axis 3 = 101W
Off-Axis 2 = 103W
Off-Axis 1 = 105W
Prime Focus = 107W
Off-Axis 1 = 111W
Off-Axis 2 = 113W
Off-Axis 3 = 116W

Stationary 12ft Dish 4
Off-Axis 3 = 121W
Off-Axis 2 = 123W
Off-Axis 1 = 125W
Prime Focus = 127W
Off-Axis 1 = 131W
Off-Axis 2 = 133W
Off-Axis 3 = 135W
Off-Axis 4 = 137W

When you finish adding all the C band feeds, don’t forget to add the Ku band feeds!
multi_focus_feed_system.JPG
off_axis_feeds.JPG
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Re: Dual and Quad Multi-Focus Scalar Rings

Post by fatso » Fri Jan 30, 2015 12:16 am

Well done Tek!

As soon as the snow melts, I'll be trying out one of these suckers!
12ft Mesh Dish
C-Band Enthusiast since 1983

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