Emitter of waves

The electromagn or radio waveses? can ticas be generated by the p? rdida of energ? to an oscillating circuit. Meaning that if it is managed to make jump a spark between two conductive wires called dipoles, take place do waves electromagn? ticas or radio waveses, in our case the dipole this formed by two rods met? licas aligned one to continuaci? n of which they do not get to touch itself. Invented by scient? fico franc? s? does douard Branly, the coherer consist of a cil tube? ndrico insulating, normally of glass, with its two bases covered inner by individual drivers together with two external electrodes. The full shaving tube met? licas that is pressed within the same.

Detector of waves

Detecci? is n of the radio waveses realised to trav? s of a simple called receiver coherer. The sensor est? constructed with two screws met? licos united by means of a tube of pl? stico is transparent. The space enters screws both fills up with iron filings, as it can turns in the following photo.


  • Rods met? licas or wire fences thickness to construct dipoles
  • A lighter piezoel? ctrico
  • Tubito hollow of pl? stico (a puntabola transparency can be used)
  • Filings of iron (or alg? n another metal)
  • A LED
  • Portapilas
  • Batteries
  • Wire of conexi? n
  • .

    C? mo to generate the waves

    Have to disarm the lighter does piezoel? ctrico to be able to have the contacts that generate the spark. To connect the contacts to two subject wires on a table, the ends of the wires are not due to be called on.

    Figure 1

    When beating does the lighter take place a spark of voltage lifted between the ends of the emitting dipole, does this fact originate the load and unloads of the dipole and the p? rdida of energ? to in the form of waves electromagn? ticas (radio waveses).


    Detectando the waves

    in order to detect the radio waveses we have to construct to the coherer Introducing iron filings in tubito of pl? stico, soon two screws are placed to both ends of tubito as it is seen in the photo of down.


    Figure 2

    Now simply two batteries and a LED along with the coherer are connected in series, as it is in figure 1


    When it is made jump a spark between dipoles placed near the coherer, radio waveses take place and these are detected by the coherer, when igniting the LED as it is seen in figura1.

    The resistance of filings inside the tube of pl? is stico very great and is the current that happens very sins? a. When the waves arrive electromagn? ticas, the resistance of filings falls and the current increases, that is to say that passes the current of the batteries and the LED ignites. As the LED stays is ignition necessary to give him sins? or blow to the coherer so that est? preparation again.

    It is possible that they must realise adjustments in tama? or of dipoles, the skip distance of the spark of piezoel? ctrico, the faying surface that present the end of the dipole receiving to filings, etc. because they influence in the operation of the detector of waves constructed. Does all the previous one condition the possible distance between the emitter of waves electromagn? ticas and the detector. Does the contact with the air superficially oxidize shavings of the coherer, which a? sla? ctricamente some of others. The layer of? xido has an effect similar to the one of a diode. When a current of radio frequency and the sufficient intensity crosses the coherer, they take place sins? you arcs between the shavings, that weld them, forming a way of low resistance between its two electrodes. That is to say, before a radio frequency pulse, the coherer happens to a state of low resistance, in principle permanent. So that the coherer can detect the following pulse, it has to happen to his state of high impedance, which secures blow? ndolo to break the microwelds formed between shavings.

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