Tefillin Waves vs. Radio Waves

Reb Eliya Lopian ZT”L once asked a talmid if a radio works ithout being plugged in. The talmid answered, “Yes!” Next, Reb Eliya asked, “If a small crystal is missing, does it still work?” The talmid replied, “No!” Reb Eliya continued, “If so, why is it hard to believe that a box on our head can channel kedushah from shomyim (heaven) without any visible connection and it does not work if a letter is missing?”