SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/hame-astable-multivibrator

Which circuit keeps switching between two states with no external clock signal?

The astable multivibrator free-runs between two states.

Start playing free

  1. Monostable multivibrator
  2. J-K flip-flop
  3. Astable multivibrator ✔

Why: An astable circuit has no stable state, so it flips back and forth on its own. That makes it a simple oscillator or clock source.

Huh, didn't know that: A monostable multivibrator switches temporarily to the alternate state for a set time (E7A06).

The dad joke
What do you say when someone asks you to build a monostable trigger circuit? I'll give it one shot.
Like this card?
Play the game

References

Answer: Astable multivibrator. An astable circuit has no stable state, so it flips back and forth on its own. That makes it a simple oscillator or clock source.

  1. NCVEC 2024-2028 Amateur Extra Question Pool, E7A05 (4th errata, Feb. 4, 2026) www.ncvec.org/downloads/2024-2028%20Extra%20Class%20Question%20Pool%20and%20Syllabus%20Public%20Release%20with%204th%20Errata%20Feb%204%202026.pdf
    D. Astable multivibrator
    Checked 2026-10-11.
  2. NCVEC 2024-2028 Amateur Extra Question Pool, E7A06 (4th errata, Feb. 4, 2026) www.ncvec.org/downloads/2024-2028%20Extra%20Class%20Question%20Pool%20and%20Syllabus%20Public%20Release%20with%204th%20Errata%20Feb%204%202026.pdf
    A. It switches temporarily to an alternate state for a set time
    Checked 2026-10-11.

Think this answer is wrong? Tap "Challenge this answer" on the card in the game and tell us why.

Test yourself in the game

Ham RadioHow long is one FT8 transmit/receive sequence?Ham RadioHow long is one WSPR transmitting period?Ham RadioThe Q65 mode is designed for which kind of signal conditions?

That's stuff everyone should know.