Real trasmissivi means

1) metallic Brace :

Draft of a brace of metallic conductors, is isolated to you between they, rests to you along the tracing of the distance established between finishes them, the used typology more are the symmetrical brace or subscriber loop that can be is opened that shielded and the coaxial brace. In vhf, for inferior distances to the 10m, the waveguides find application while for inferior distances to the 10cm the microstrips are used also. Often the conductors of a bifilar brace are dipped in insulating polyethylene that of it increases the uniformità, moreover come interlace to you in order to reduce the diafonie.

 

2) Function of transfer of perfect trasmissivo means:

for f_m < f < f_M

where L is the length of the log of line and to₀ its constant of attenuation, it assumes moreover that in the line is guided propagation of a single way TEM.

 

3) characteristic Largenesses of one metallic brace :

Stiffness caratteristica

Constant of propagazione

Time of ritardo

Time of delay of gruppo

Speed of fase

Speed of gruppo

Length of onda

Length elettrica

 

4) primary Parameters of the line :

r axial resistance to length unit

l axial inductance to length unit

g conductance of cross-sectional dispersion to length unit

cross-sectional ability to length unit

the values assumed from r depend on the frequency for f > 10kHz while the other parameters of are almost independent.

 

5) Effect to pellicolare :

In the ideal conductors s it is infinite and the current density is not null single on the separation surface and directed axially, in the real conductors s it is much elevating but ended therefore the distance is had that the current density is not null also to the inside of the conductor but decreases esponenzialmente going away from the surface, in particular to which j it is reduced to 1/e of its value on the surface it is called thickness of penetration and it diminishes to growing of the frequency, in particular for f > 10kHz it is had that d_m are greater of the dimensions of the conductor.

 

6) of a single conductor with contour and unitary axial Resistance section of area of perimeter C :

For vlves is had while for vhf it is necessary to consider the effect to pellicolare that it shrinks the section of the conductor in particular if C is the perimeter of the conductor has an area equivalent Cd_m therefore the axial resistance becomes , is observed therefore that the conductor in vhf introduces a greater resistance, that in coaxial cables it implies schermaggio regarding interfering vhf but regarding the lowlands in order not to shield which are necessary coverings with high magnetic permeability.

 

7) Relation between the primary parameters and the secondary parameters :

it is observed however that in both the equations g are negligible in the sums in how much infinitesimal one.

 

8) Conditions that guarantee one perfect transmission on one real line:

In useful band of it marks them the line must introduce characteristic following:

to)       real characteristic stiffness and constant Z_c = R

b)       constant of independent attenuation from the frequency

c)       constant of phase proporziona them to the frequency

 

9) Conditions of Heaviside on the primary parameters:

With the aim to obtain a real characteristic stiffness and constant Z_c(f) = R enough to place the argument of the equal root to ²R cioè from which ottiene a line that satisfies the conditions of Heaviside respects also the other conditions that guarantee the perfect transmission in fact and .

 

10) asymptotic Model to vlf :

In the expressions it generates them of the characteristic stiffness and of the propagation constant g it can be neglected like also since w®0 are had r_b > > wl where is replaced, is had:

it is observed that it is the real part of the propagation constant (…that coincides to the constant of attenuation to) that the imaginary part (…that coincides to the phase constant b) is proporziona them to the root of the frequency while for having the ideal transmission, first would have to be constant while the second one would have to be proporziona them to the frequency.

11) asymptotic Model to vhf:

In the expressions it generates them of the characteristic stiffness and of the propagation constant g it can be neglected like also since w®¥ ha r_b < < wl therefore multiplying the constant of propagation for and applying the development in series of Mac Laurin , is obtained:

it is observed is that Z is constant and real and also that b is two characteristics proporziona them to the frequency therefore these are optimal for the perfect transmission unfortunately the constant of attenuation to depend on the frequency through and therefore does not respect the condition of perfect transmission.

 

12) Relation between the largenesses of the asymptotic model in vlf and the largenesses of the model in vhf :

where dictates crossing frequency is such that only if it marks them to transmit has a clearly external band to such frequency can be used the correspondent model. Bringing back on two diagrams the asymptotic courses of |Z_c| , to e b it is observed that the behavior to vhf of the metallic brace is next to the perfect behavior but implies greater attenuations.

 

13) Characteristics of the symmetrical braces:

It is necessary to replace in the found relations the areas and the perimeters of this particular structure, are obtained:

the frequency of crossing for cables with comprised diameter d between 0,4mm and 1mm is always smaller of 6kHz therefore for marks them telephone having B=[300Hz band, 3400Hz ] pu² to use the asymptotic model to vlf.

 

14) Characteristics of the coaxial braces:

It is necessary to replace in the found relations the areas and the perimeters of this particular structure, are obtained:

in particular using the asymptotic model in vhf one finds that the attenuation constant is minimal for . In the attempt to diminish the losses the conductors come moreover separate to you with dielectric floppy disks, in such a way and_r @ 1.1 and 75Z_to =W . In the applications on short distances it is used instead the full dielectric and_r = 2,26 and 50Z _to =W in how much introduces better mechanical flexibility.

 

Fiber optics

15) Constitution of the fiber optic :

The fiber is constituted from an inner nucleus âCOREâ? having had diameter 2a and ₂ refractive indexn ₁ >n ₂ beingn l' refractive index of the having cape âCLADDINGâ? diameter 2d @ 125mm, the diameter of the produced fiber is the double quantity in how much it is much fragile one and comes therefore covered with an opaque dielectric covering to the employed frequencies that therefore it acts as also from screen.

 

16) relative Difference of the refractive indices :

in fibers to light variation of the refractive index D < < 1 in how much note n ₁@ n ₂is had .

 

17) Ways guide to you :

Making reference the standardized frequency it is had that propagano only m having ways one frequency of cut standardized inferior to the frequency of cut standardized of mark them. Everyone of m the ways has one constant of phase bthe (f) that verification the where the first equality verification to the cut and the second one for f®¥ .

 

18) Constant of standardized phase :

The constant of phase b of i-esimo the way discosta little from the constant of intrinsic phase kn_{2 ,} in order to evidence the scostamento is rerun then to the constant of phase normalizzata from which pu² gaining itself . This last one concurs to evidence the 2 typology of present dispersions in fibers in fact i-esimo the guided way introduces a group delay

= the 0, 1, 2 … , m

if we consider a single way scompare but it sees that both the terms are functions of the frequency and therefore intramodale or chromatic dispersion is had, considering more ways then looks at that the solo 2 * term from intermodal place to dispersion.

 

19) Constant of attenuation of one fiber:

where P_devout is the lost power in a distance of unitary length because of the energy that is transformed in heat or that it comes irradiated. In particular the radiation happens because of small variations of the refractive index that gives place to the spread of Rayleigh and whose attenuation is proporziona they to l^-4 . The absorption has had scattering reticular (ultraviolet), scattering molecular (infrared) and to presence of Ionian ossidrili OH^- . Initially m in as far as such wavelength were workedin 1ª window l = 0,85 m emit the GaAs, are then pass to you in 2ª window l= 1,3mm where the minimum of the dispersion is had and in 3ª window l= 1,55mm where the minimum of the attenuation is had.

 

20) Model of one approximated fiber optic with the geometric optical:

Fibers with much large one concur the propagation of many ways, to everyone we associate a beam and we see that so that propaghi is necessary endures a reflection total to the interface nucleus-cape, that happens if the angle of incidence regarding the normal school is greater of that it only happens for the beams that are introduced to the income of the fiber with an inferior angle j to the angle of acceptance of the fiber j_To whose breast is called numerical opening . With the geometric optical it is always possible to calculate the delay of group maximum .

 

21) multimodali Fibers:

A multimodale fiber is characterized from a trasmettenza , supposes that x are constant and that the constants of attenuation to are independent from the frequency, if of it derives that the transmitted impulsive answer is from which it is observed that the means are affection from intermodal dispersion.

The maximum value of the delay between 2 ways obtains from , observing that is comprised between 0 and 2 but mostly between 1 and 2 obtain that the maximum variation of the group delay is that limits the employment of multimodali fibers to inferior drafts to 100mt where the relation is verified .

 

22) monomodali fiber Utilizzo:

If the standardized frequency used is V<2,405 it has that in the fiber propaga alone the fundamental way, therefore will not have intermodal dispersion while it more frequently becomes the intramodale dispersion also said evidenced chromatic dispersion from the or much from the coefficient of chromatic dispersion importantwhere is the coefficient of chromatic dispersion of material, negative for l < 1,27mm and positive beyond mentre it is the coefficient of chromatic dispersion of guide that is a value always negative, adding the two contributions is observed that one exists l > 1,27mm for which the coefficient of chromatic dispersion is null. In fiber optics to moved dispersion it is acted on the drogaggio with the aim to vary the refractive index and to move this minimum to l = 1,55mm that is in 3ª window.

 

23) Typology of optical sources:

They are substantially two, the diode valve led which being little directive it finds application exclusively in the multimodali fibers, and the diode valve laser that are characterized from extreme direttività and therefore comes used in monomodali fibers.

 

24) Typology of fotorivelatori:

The diode valves pin in the which every photon are used generate a brace electron-gap and the diode valves avalanche in the which every photon from place to many braces electron-gap but it increases the noise.