Definition
The frequency at which the current gain of a transistor in a common-base configuration drops to 0.707 (about 70.7%) of its low-frequency value. Above this frequency, the transistor becomes progressively less effective at amplifying a signal.
Plain English
The point on the frequency scale where a transistor starts to lose its ability to amplify cleanly. Below it, the transistor works well. Above it, the signal it puts out gets weaker and weaker compared to what goes in.
Context Anchor
Seen in avionics electronics, radio circuits, and maintenance specifications for transistors or signal circuits.
Derivation
‘Alpha’ is the symbol used in electronics for the current gain of a transistor in the common-base configuration. ‘Cutoff’ marks the point where useful performance ends. So ‘alpha cutoff frequency’ literally names the frequency where alpha (the gain) cuts off.
Why Pilots Care
Pilots don’t set this value, but it determines whether a piece of avionics can handle the radio frequencies it’s designed for. A transistor used above its alpha cutoff frequency won’t amplify properly, which is why avionics components are matched to the frequency ranges they operate in.
Analogy
It is like a speaker that still works as the pitch gets higher, but reaches a point where the sound has clearly weakened compared with its normal level.
Intuition Check
Alpha does not mean angle of attack here. In this electronics term, alpha means a transistor’s current gain in a common-base circuit.
Example Sentence 1
The technician selected a transistor with an alpha cutoff frequency well above the VHF communication band so the radio would amplify cleanly across all operating frequencies.
Example Sentence 2
Replacing the aging transistor raised the alpha cutoff frequency and restored reliable VHF reception.