How to choose a satellite dish

How to choose a satellite dishSatellite television, like terrestrial or cable, is transmitted from the antenna to the TV via cable. Have you often thought about what cable you are offered to buy when you need it? But the seller will often praise their goods as soon as they can. And to a reasonable question, is it a good cable, you still get a clear, unequivocal answer - a good one. Have you often received a bad answer from the seller of sausage? What does a good cable mean? Good for what? Today there are many stereotypes on the market for coaxial cable for TV.

 

One of them is a copper cable better. This error went even from electricians, for whom, the thicker the cable core, the more current can be passed through it. But this is all true for wiring in the house. Regarding the transmission of high-frequency signals through a cable, the thickness and amount of copper in the central core is almost irrelevant. As a rule, high-frequency currents penetrate the fractions of a micrometer deep into the central core and the presence of copper 8 in its middle does not have any effect on the cable carrying capacity. In other words, the attenuation of a useful signal.

 

The second misconception is that the Soviet or domestic cable is better than the imported one. Here it is necessary to compare specifically two cables with each other. An important role in attenuation of the signal has a shielding density of the central core. That domestic cable for home use, which everyone remembers called RK (radio frequency cable) has never had 100% shielding. In import cables, in order to increase the shielding density, an additional foil shielding is used. The foil is located between the insulation of the central core and the shielding braid. Here it is important, the foil is actually a lavsan film painted with metallic pollen. Over time, sputtering simply dissolves into the air from lavsan, and the parameters of such a cable deteriorate significantly. The most expensive cables have triple shielding in the form of a layer of foil, braid, lavsan and another layer of braid with foil.

 

The third misconception is that through any cable you can feed both a television signal and a satellite one. Without going deep into physics, it is worth noting that the higher the signal frequency, the greater is its attenuation per linear meter of cable.So, if we take the domestic cable RK, and in fact he still has a bunch of additional designations after these two letters, then, having carefully examined its characteristics, we will see that it cannot pass through itself without significant losses, starting from the distance a Hume decimeter signal. At the exit it simply will not be. What to say about the satellite signal, which is an order of magnitude higher than the decimeter TV band.

 

The fourth misconception is that the black cable is designed for outdoor use. And that's why it's eternal. Black or white is just the color of paint that is added when making the outer insulation of a cable. In fact, an important role is played by additives when casting insulation, which give the cable UV strength, frost resistance and heat resistance. All these additives cost a lot of money. Therefore, those who are trying to get a cheap cable at the outlet will never add additives to the cable material. This also applies to the insulation of the central core. After all, even its chemical composition depends not only on the mechanical parameters, but also on the attenuation of the signal in the cable as a whole. Therefore, the internal insulation in high-quality cable is made of more expensive materials.

 

From here you can make a simple conclusion.It is not the country of the cable manufacturer that is important, it is important not the presence of a fully copper conductor in the cable, or even the color of the cable. What really matters is its quality, what it is made of and how it is made.

 

To get more income and less expenses, dishonest manufacturers, producing cheap cables, without investing in increasing durability reliability and less signal attenuation in the cable, draw on it marking more expensive and high-quality products. Thus, introducing the buyer into deception, getting super-profits, because the labeling is a good and expensive product, and in fact, after six months, the internal destruction of the cable begins. The material begins to decompose physically, releasing the gas, which is odorless and harmful to the human body. Within six months, the cable loses up to 40% of its strength and up to 60% of throughput. That is, it increases the attenuation of the useful signal at the same input signal level. And also its geometry changes. In the section, it is close to the ellipse and far from an even circle. Which again impairs the bandwidth of the cable.

One of the common methods of selling poor-quality cable is changing the labeling by one letter from the already known and popular more expensive and high-quality cable of a well-known brand.Similar to the destination product is at the same time very low quality. Since this is done intentionally, this is pure fraud. Swindlers rely on the inattention of the simple buyer. Usually, Chinese artisans are engaged in this, but the temptation to use someone else's popularity to raise their own sales is so great that our home-grown Ostap Benders also decided to master the unintelligent type of cheating.

We got two 100 meter bays of such a cable with a difference in one letter in the name and consonant with the FinMark brand cable. It is regrettable that the quality of a fake cable, to put it mildly, leaves much to be desired and is at the level of cheap low-grade cables. And the difference is that there is almost no RG6 that F660. The only difference is in the number of screen delays. Compare in detail.

 

Consider the differences between fake and original

 

 

Resistance to direct current directly depends on the amount of copper in the coating of the central conductor. Why is this parameter important? First, the thickness of copper directly affects losses in the low-frequency region. And if this is not the main thing for ordinary TV, then for transmission of video signals, a reverse channel, power supply, this already plays a significant role.Secondly, the copper layer protects the steel core from corrosion, and the degree of this protection also directly depends on the coating thickness.

 

It is seen that for the RG-6, that for the F660, the same central conductor with the minimum thickness of the copper coating is used in the fakes.

The loss graphs confirm this.

Losses

Let's compare the loss characteristics in the range up to 1000 MHz.

Braid

 

There is a clear savings in materials. And, although the number of wires in the sheath is the same, but the calculation is made that the consumer will not notice any hundredths of a millimeter. Also save material, while increasing the pitch of the sheath. But this savings leads to a decrease in filling, and instead of 60% filling we get obviously less. The reduced diameter of the braid wires also reduces their mechanical strength, and in the case of ingress of moisture (for example, through an improperly installed connector), corrosion leads to faster destruction. The difference in the amount of metal braid is clearly visible when measuring the ohmic resistance of the braid. This is also important when power is supplied via cable, for example, in individual satellite reception systems. Due to excessive voltage drop, the satellite converter may simply not switch to horizontal polarization with a sufficiently long line.

 

Foil

As part of the screen, the foil provides improved cable shielding. What's the Difference. In a fake cable, lavsan-based foil, which is more slippery in its properties, allows the cable elements to move relative to each other. Even the F660 fake sample of half a meter length can be disassembled into its component parts by pulling the guts.

And most importantly, in the fake F660, as in the usual RG-6, the foil is not glued to the dielectric. This design, in addition to reducing the mechanical resistance to longitudinal loads, does not allow the normal installation of high-quality crimp and compression connectors.

 

Dielectric

 

 

Analyzing the cable loss graph, we see that a fake cable has increased losses not only at low frequencies (due to a decrease in the thickness of the copper layer), but also at high frequencies. Usually losses at high frequencies are determined by losses in the dielectric and depend on its quality. Indeed, carefully examining the dielectric counterfeit, you can detect blotches of a different color, which usually happens when adding recycled polyethylene.

To compare the strength of the shell, simply try to break the one and the other.8 more expensive cables F660 PVC sheath is of higher quality than cable RG-b, there is no difference in fake; One low grade PVC is used for both types of cable.

On bays of a fake cable, as a rule, there is a boastful inscription about cold-resistant PVC. If the manufacturers meant that the cable does not crumble in the cold, then yes, it does not crumble. But at a negative temperature, the cable becomes so rigid (like a spring) that an attempt to bend it with a small radius leads to a room of entrails and irreversible deformation. Therefore, work in the cold with such a cable requires specific handling.

The considered cable type RG-b is the most ordinary representative of cheap cables with minimized content of non-ferrous metals and mediocre quality of materials. Losses in such a cable are 2-ZD6 higher in the entire frequency range compared to the FinMark cable.

The considered cable of type F660 is a low-grade raw material, in reality it is the same cable as the RG-6, only with an increased number of wires in the screen.



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