There must also be something to trigger the transponder into replying like a SSR radar or a TCAS equiped aircraft. If you dont have either of those then unit will not work!
My guess is that it would only work within range of a ground based radar facility or if an aircraft with operating TCAS is within range....?? Sydney or Melb area no prob... Tamworth or Broken Hill - I doubt it. In the USA this is not such a problem.