The best place to get parallel power to the motor is a **DiSEqC** switch, but since it is not capable of passing large currents, it needs to be finalized.

Using an awl and a scalpel, carefully remove the spring-loaded cover of the switch so that it can be reinstalled in its original place:

In the places indicated by the red arrows, we cut the printed conductors, and in the places indicated by the blue arrows, we solder additional elements:

Between the power point of the control circuit of the switch and the central output of the 4th port is the inductor L1, which passes the direct current of the motor supply and the pulses controlling it with a frequency of 22 kHz, but is an infinitely large resistance for the RF frequency;

In the break of the signal line from the switching diode to the 4th port - capacitor C1 with a capacitance < 1000 pF so that the motor power does not open the switching diode;

Between the printed inductance to the left of the 4th port and the signal line between the capacitor C1 and the switching diode - inductance L2, through which the opening voltage is supplied from the control circuit in the presence of the command “switching the 4th port to the **DiSEqC** output of the switch”

Elements 2 and 3 allow you to connect a fourth LNB through the second motor connector. I connected an LNB with a director to the 4th port to receive the** MITRIS** “terrestrial” DVB-S2 broadcast system:

As you can see in the photo, the drop cable goes to the output of the converted DiSEqC switch, the focus LNB Inverto Black Ultra is connected to the first (connected by default) port; a multi-feed LNB with a depolarization plate is connected to the second port to receive circular polarization signals; an LNB with a director is connected to the third port to increase the signal in the “far” multifeed, and the cable from the 4th port goes to the ** WinQuest** motor and from the second connector to the LNB with a director, which is directed to the

The following shows the frequency response of the second channel (without a motor in the RF circuit) - on the left and the fourth channel (with a motor in the RF circuit) - on the right:

Due to the poor matching of **OMICOM S2** with the wave impedance of the cable, intense (up to 2.7 - 3.3dB at high frequencies) standing waves appear in it, which are a source of in-band interference. The uneven frequency response reaches 5 - 6dB. The inclusion of the motor in the RF circuit catastrophically distorts the frequency response ...

The difference in frequency response was obtained without and with a motor in the RF circuit:

After registering the spectra and parameters of the transponders, the setup was converted to parallel power supply of the motor through the 4th port of the **DiSEqC **switch:

Look how favorably the frequency response has changed - the total unevenness has decreased from 13 to 9dB, the amplitude of standing waves has decreased from 3 to 0.7dB:

Now you can see how the parallel power supply of the motor affected the reception of real signals.

After alteration of the installation, the unevenness of the amplitude-frequency characteristic decreased by 1 dB for V and 2 dB for H polarizations. The signal level, on the contrary, increased by 2-3dB for V and 1-3dB for H polarizations:

The number of found transponders increased by 2, and the number of blocked ones - by 5 units

Average **SNR**av =14.9dB (0.5dB more) and **LM** headroom =8.2dB (0.4dB more) :

The average **SNR** level has grown to 13.8dB, the lock margin is up to 6.9dB, the number of locked transponders is up to 60:

The number of found transponders increased by 3, and the number of blocked ones - by 7 units

Average **SNR**av =13.8dB (0.7dB more) and **LM** headroom =6.9dB (0.7dB more) :

To evaluate what the addition of two wire spirals and one PCB capacitor to the DiSEqC switch gave, I note that increasing the sensitivity of the receiving installation by 0.7dB is equivalent to increasing the diameter of the antenna aperture from 105cm to 113cm

]]>If the LNB is not in the geometric focus of the parabolic antenna, then we will adjust the antenna not by the true azimuth and elevation of the satellite, but by choosing the "best" position of the LNB around this initially incorrect point, we will tune to the maximum multi-feed pseudofocus.

Do it right like this:

- according to the calculated elevation angle of the vertex satellite and the offset angle of the mirror, set the deviation from the vertical of the parabolic mirror cut and do not touch this adjustment in the future;

- install LNB strictly in the plane of symmetry of the parabolic mirror and direct the axis of the first one to the aiming point on the second one;

- by changing the antenna azimuth within +/- 3° from the calculated one to the summit satellite, adjust this parameter to the maximum signal and do not touch this adjustment in the future;

- moving the LNB along the line of sight to achieve the maximum signal. At this moment, the geometric focus of the parabolic mirror will be aligned with the phase center of the feed.

According to my experiments with LNB ** Titanium TSX, Inverto Black Eco, Inverto Black Ultra, Megasat, Orton,** etc., their phase center is in the plane of the cut of the plastic casing where it passes to a diameter of 40mm. This is approximately in the neck of the conical horn or in the middle of the mod transformer as in the

Some theory of wave propagation:

QuoteThe

eikonalequation (ancient Greek εἰκών) is a non-linear partial differential equation encountered in wave propagation problems when the wave equation is approximated using WKB theory. It is a consequence of Maxwell's equations, and connects wave optics with geometric optics

Recall that light is electromagnetic waves with a very short wavelength, but this wave process is much closer to the Ku range than the waves that propagated in a cantilevered beam and, thanks to Poisson's brilliant solution, laid the foundation for the theory of wave propagation.

QuoteGeometric optics is the branch of optics that considers the wavelength to be negligible. The basis of geometric optics is the

eikonalequation.It follows from the

eikonalequation that geometric optics is applicable only for short wavelengths. The shorter the wavelength, the more accurate the geometrical optics approximation.

It follows from the solution of the ** eikonal** equation that the wave process propagates along the ray tubes:

where** r(s)** is the beam, **dƩ** is the cross section of the beam tube.

Of the properties of a ray tube, the most important for us is that the wave energy propagates exclusively along the ray tube, without flowing through its side walls, and the energy density inside the ray tube is inversely proportional to its cross-sectional area **dƩ**.

A ray tube can be compared to a river in which the water does not flow over the banks and which flows slowly and smoothly where the river is wide and deep, but rushes with a roar in the gorge, where the banks converge between the cliffs ...

Let's ask ourselves the question: "What is the minimum radius of the ray tube?" - by answering which, we will get the key to solving the problem about the position of the phase center (PC) of the irradiator

I have derived a formula for determining the position of the phase center relative to the horn:

** ∆Z=0.293λ/sin(α/2)**,

where

** ∆Z** - displacement of the PC from the top of the cone inscribed in the receiving horn;

** λ **- wavelength;

** α** - opening angle of the cone.

Based on the results of practical tuning of the long-focus antenna CA-902 with LNB ** Inverto Black Ultra**, I was convinced that the best alignment results are obtained when the geometric focus of the mirror is on the feed axis in the cut plane of the back wall of the LNB feed housing, where the diameter begins 40mm.

In the drawing, this plane is marked with a blue dotted line (at a distance of 26 mm from the irradiator cut):

The figure shows the results of calculating the DP of a corrugated irradiator using the **SABOR** program, a frontal photo of the ** Inverto Black Ultra** irradiator and a drawing of its longitudinal section according to the measurements I made using a caliper.

In the drawing, the irradiator aperture cone** Alpha**=62° is limited by gray lines -10dB Width 69.4° at 12.44GHz

The position of the phase center (**ФЦ**) of the irradiator is shown by red circles for the extreme frequencies of the range 10.7 and 12.75 GHz (** Lambda** = 28 and 23.5 mm, respectively)

The distance from the phase center to the top of the cone ** dXфц** is calculated according to my formula, where

As you can see, the best LNB alignment results were achieved with alignment of the phase center for the highest frequency of the range with the geometric focus of the parabolic mirror,

moreover, the axis of the irradiator lies on the line of sight

Let's summarize:

1. A wave propagates along a beam only when its frequency is infinite.

This is confirmed in geometric optics, where the frequency of an electromagnetic wave tends to infinity.

2. A wave with a finite frequency (as in our case) propagates along the ray tube, and the energy of the electromagnetic wave cannot flow through the "walls" of the ray tube.

3. There is a minimum diameter of a ray tube in which an electromagnetic wave with a given wavelength can propagate. This takes into account the coefficient in front of the ** Lambda** in the formula I derived based on the solution of the

4. The phase center is defined as the point of intersection of the axes of the extreme wave tubes in the feed. The red dots show the phase centers for a wavelength of 28mm (**ФЦ****-****28**) and 23.5mm (**ФЦ****-23.5**) - this is for the cutoff frequencies of the Ku band.

5. The opening angle of the irradiator is** 62°**.

6. The correctness of my formula for determining the position of the phase center is confirmed by the practical results of adjusting my antennas.

7. The accuracy of the formula is confirmed by the results of computer simulation of wave fields.

The calculations in the** Ansys HFSS** program according to my data were performed by

In the figure, thin black circles show the lines of equal phases of the wave field (isophase surfaces).

Their centers coincide and are in the phase center of the irradiator (yellow circle)

As you can see with the naked eye, the position of the phase center in the figure perfectly matches the one calculated by my formula

The animation shows the process of emitting a wave field from the irradiator with the geometry of** Inverto Black Ultra**:

Unfortunately, in the** Ansys HFSS** program, the center of NOT isophase, but isoamplitude lines is determined, which is erroneously called the phase center of the feed

This can be clearly seen in the animation, which shows two spheres centered at the "pseudo phase center" (white circle or red cross), which does NOT coincide with the true PC (**ФЦ**) :

]]>

What does optimal mean? - these are parameters that, depending on the task at hand, will…]]>

What does optimal mean? - these are parameters that, depending on the task at hand, will provide either the maximum accuracy of determining the parameters of transponders at an acceptable speed of their search, or the maximum speed of constructing spectra of satellite signals with the condition of finding all above-threshold transponders, or determining the parameters of subthreshold signals, or searching for ultra-low-speed ( up to beacons) transponders to ordinary PCI (ex) cards, significantly exceeding the manufacturer's declared characteristics of** DVB S2** signal tuners and demodulators. So, for example, the frequency step of the spectra from 1000 kHz has been brought to 4kHz (reduced by a factor of 250), and the resolution in the **HR** (high-resolution) mode has increased tenfold.

In this article (and there are several planned) we will consider the selection and installation of two parameters: the Noise level and the minimum value of the RF signal power.

*An example of determining the Noise Level and Min level RF*

First, we set the frequency range in which we will work **(Fstart** - **Fstop**) and the frequency step per one pixel of the **dF** graph: 11200 - 11450 MHz and 499 kHz. By clicking the **Apply** button, we get the layout of the spectra plate in the upper left corner of the screen. Select the 1 MHz spectrum frequency step in the** Frequency step, MHz** field and press the **Spectrum** button - after a few tens of seconds, the RF spectrum will appear on the screen (blue curve).

Using the slider on the right side of the tablet, move the dashed purple line of the power level of the analyzed spectrum frequencies (RF threshold) so that it is below most of the minimums of the RF spectrum (-50.5 dB). After that, use the** Blind Scan** button to launch a "blind" scan of the spectrum.

The blue outlines of the detected transponders start to appear on the screen. Their height is equal to the SNR of the found transponders, the "legs" are placed on the bandwidth occupied by the transponder, and in the middle between them (at the carrier frequency) there is a noise level point. The vertices of the transponders are tied to the RF spectrum, and through the points of the noise level, I drew a gray line, which is close to the noise level in the studied frequency band.

Then the green line of the average noise level was drawn so that it was, if possible, below all the minimums of the RF spectrum, and the areas of the figures, which are limited by the gray noise line, above and below the green line were approximately the same. The height of this line is the** Noise Level**, which we enter in the corresponding field of the main program window.

The amplitude of the spectrum above this line can be adjusted with the **Scale RF** parameter to emphasize the wanted signals, and the dynamic range of the output below the **Min level RF** is non-linearly compressed for visual noise suppression, which improves the readability of the spectrum. In addition, the **Min level RF** is used in spectrum deconvolution to deepen the minima between adjacent transponders.

**Min level RF** is recommended to be selected equal to or less than the **Noise level** of the receiving installation relative to the **Noise Level **