3 replies to this topic

[pieterjan456]

I'm currently learning my avionics course and am at the Distance measuring equipement. All good, i know the aircraft sends pulses instead of one signal, but if multiple aircraft are interrogating the DME station, how does the aircraft 'know' its his code which is send back and not the signal of another aircraft? Is there like any identity code send with the signal?

[Chief_Bean]

The signature of the interrogation pulse differs from aircraft to aircraft as far as I know. The return pulse from the DME needs to match the interrogation pulse.

[Peter797]

If I remember correctly from my avionics class, what happens is:

-----PULSE1-----PULSE2---------------------------jitter-----------------------------PULSE1-----PULSE2-------

The "jitter" is unique to every aircraft, and that is how they are distinguishable. What happened, was the resistances in each aircraft's DME equipment were different, so the jitter can be from 9-11ms in length depending on the resistances encountered.

With today's technology, I'm pretty sure my professor mentioned that they are able to actually specify the length of the jitter to their own specifications.


Did you learn about the "x" and "y" spacing between pulses, and how the x space from the beginning of PULSE1 to the beginning of PULSE2 is 12 microseconds and y space is 36 microseconds yet? Because with that, we then also get X and Y channels.


Ahh CORRECTION:


In modern systems, the aircraft registration is encoded in the jitter value.

Edited by Peter797, 30 May 2013 - 11:54 AM.

[AmericanAirFan]

Ah fond memories of my avionics class. That all sounds about right.