SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/hame-phase-locked-loop

What is a phase-locked loop?

A servo loop that locks an oscillator to a reference.

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  1. A ratio detector with a reactance modulator
  2. A precision push-pull amplifier
  3. A servo loop with phase detector, filter, VCO and reference ✔

Why: A phase detector compares the VCO with a stable reference. A low-pass filter smooths the error, which steers the VCO until it locks on.

Huh, didn't know that: A phase-locked loop can perform frequency synthesis and FM demodulation (E7H06).

The dad joke
What does an electrician say when your house loses 240 volts but the power company is working on it? It's just a phase.
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References

Answer: A servo loop with phase detector, filter, VCO and reference. A phase detector compares the VCO with a stable reference. A low-pass filter smooths the error, which steers the VCO until it locks on.

  1. NCVEC 2024-2028 Amateur Extra Question Pool, E7H03 (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
    C. An electronic servo loop consisting of a phase detector, a low-pass filter, a voltage-controlled oscillator, and a stable reference oscillator
    Checked 2026-10-11.
  2. NCVEC 2024-2028 Amateur Extra Question Pool, E7H06 (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
    B. Frequency synthesis and FM demodulation
    Checked 2026-10-11.

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