单项选择题
A.Bell alarm to warn the user B.Lighted alarm signal to warn the user C.Alternate signal keying system D.View finder for each station
A.Less signal energy is necessary for receiver operation B.More signal energy is available at the receiver C.It significantly increases the peak power D.It increases the signal capacity
A.Reflected electron B.Electrical radiation C.Quarterpoint electrical navigation D.Hyperbolic radio navigation