A FD detector does not require manual tuning as it works on a full range of bat frequencies, but some, like the Duet, also have a heterodyne detector built in.
12.
Prior to widespread use of synthesizers, radio and television receivers relied on manual tuning of a local oscillator, which used a resonant circuit composed of an inductor and capacitor, or sometimes resonant transmission lines; to determine the frequency.
13.
Before a scan is done, it may be possible to access the programs directly by manual tuning, by entering 43-1, 43-2 . . . After the scan, the programs would usually be accessed by entering 4-1, 4-2 etc ., but it may still be possible to also access them directly at 43.
