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q4765 Radio signal classification

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  • q4765 Radio signal classification

    Hi! I would like to be sure of one thing:
    Is there any mistake in the radio signal classification given in example in this question? 1A1 does not exist but it should be A1A instead?!
    In accordance with the International Telecommunication Union (ITU) a radio signal can be classifired by three symbols. The first symbol indicates: (eg 1A1):
    1. type of information to be transmitted.
    2. type of modulation of the main carrier. is said true
    3. type of modulation of the secondary carrier.
    4. nature of the signal modulating the main carrier.

  • #2
    Re: q4765 Radio signal classification

    q7226 is almost the same. The example is normal this time. (A1A)

    Comment


    • #3
      Re: q4765 Radio signal classification

      It is definitely A1A, the full designators for NDB's being:

      N0N A1A

      N0N A2A

      In both cases, the first part of the designator refers to the signal which is the Direction Finding component:

      N = Emission of an unmodulated carrier
      0 = No modulating signal
      N = No information transmitted

      The second part of the designator refers to that part of the signal used for the identification of the signal.


      A = Double-sideband
      1 = A single channel containing quantized or digital information without the use of a modulating sub-carrier
      A = Telegraphy - for aural reception

      A1A was used on older and long range NDB's where the IDENT was transmitted by keying or breaking the carrier wave into a series of dots and dashes at 10 second intervals. As the carrier wave frequency is out of human audible range a process known as heterodyning is used to mix a second signal (+/-2 kHz) with the carrier wave and outputting the difference between the two signals in sympathy with the keyed carrier wave as an audible Morse Code IDENT. This requires the ADF's mixer circuit (BFO - Beat Frequency Oscillator) to be switched on.


      A = Double-sideband
      2 = A single channel containing quantized or digital information with the use of a modulating sub-carrier
      A = Telegraphy - for aural reception

      A2A is used on more modern equipment and also uses a keyed Morse Code IDENT but instead of heterodyning a sub-carrier is Amplitude Modulated at an audible frequency, in sympathy with the keying. It does not require a separate BFO circuit to be activated.

      That's a tad more in depth than you need to know but it's all good stuff.

      Best Regards,

      Tony Pike

      Give Sergei back his dignity......Simples!

      Comment


      • #4
        So, in simple words, a singal from an NDB has two carrier waves, then N0N part and the A1A or A2A?
        Which means that in fact we are talking about a..double signal?

        Comment


        • #5
          Not quite.

          Radio signals have one carrier wave, the carrier wave is used to carry the information. This is the NON bit. Information is added to the carrier wave by a process of modulation this is the A1A or A2A bit. In the case of the A1A, the information is put on by interrupting the carrier wave, in the form of Morse code. In the case of A2A the information is added by superimposing another frequency onto the carrier wave by varying the amplitude (strength) of the carrier wave.

          An analogy might be to think of when messages were sent by pony express. The pony represents the carrier wave, and the bags which modify the silhouette of the pony contain the message.

          A definition of modulation might be: the technical term for the process of impressing and transporting information by radio waves.

          You are required to know the definition, and that in radio navigation there are four ways of modulating a carrier wave; amplitude, frequency, pulse and phase

          I hope this helps.

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