-b- wrote:

Thumbing through a 1962 FLYING magazine, I came across an
advertisement for the all-new Motorola M-400 NAV/COM. Among other
quaint features, such as the 100KHz spacing, later upgradeable to
50KHz, and the COM transmit frequency that automatically switches to
122.1 any time you select a NAV frequency "so you don't have to be
continually switching back and forth between your Com and Nav
frequencies!" I am puzzled by the all-new feature; Crystal Tuning so
you can dial-in your frequency. "No more whistling for a channel;
just dial your frequency and you're on!"

A cursory web search didn't reveal anything about this.
Who can enlighten me about this "whistling for a channel" business?


It's referring to "whistle stop tuning", introduced by NARCO, I believe, in
the late forties or early fifties. Back then you'd transmit on one of
four(?) crystal-selected frequencies but select the receiver frequency on a
tuner that covered both nav and voice bands. Activating "whistle-stop
tuning" turned the transmitter on at very low power, when the tuner reached
the transmitter frequency you heard a whistle and knew you were on the right
frequency.