Brian Whatcott wrote:
-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?

Thanks

This is a speculative, yet plausible response.
Transmitters without a crystal per channel might yet have a crystal
controlled comb generator, which when manual tuning, would null a beat
frequency whistle when on frequency.

Brian W

The Narco whistle-stop radios had a limited number of transmitter
crystals (9 for the SuperHomer and 27 for the Omnigator). The receiver
tuner was analog. So, if you pulled out the whistle-stop button as you
got close to the selected transmitter crystal the whistle-stop tone
activated.