Listening to FM Radio with the UHFLI 600 MHz Lock-in Amplifier and PLL

A guy at Zurich Instruments soldered a 3.5mm headphone socket to a BNC cable and attached a 75-cm antenna wire to the Signal Input of our 600MHz UHFLI Lock-in Amplifier with UHF-PID PID/PLL option and was happily listening to FM radio. Abuse alert! I instantly had to copy that one.

Zurich Instruments Lock-in Amplifier Frequency Sweep.

The Zurich Instruments UHFLI Lock-in Amplifier can also be used as spectrum analyzer.

The procedure is quite straight forward. You can use the PLL with its ~200 kHz PLL tracking bandwidth to track the FM radio signal and output a voltage proportional to the frequency deviation dF onto a head phone with, i.e., 1 uV/Hz. This yields a high-fidelity, crystal-clear mono sound.

Here is how it works

    1. Connect an unshielded wire of ~0.75 m length to the Signal Input 1
    2. Start UHFLI in default config (Signal Input 1: 50 ohm, 1V range)
    3. Sweep for radio stations:
      • Points: ~600
      • Log: off
      • Frequency sweep range:
        • Japan: 76 MHz to 90 MHz
        • East Europe: 65.8 MHz 74 MHz (being deprecated and adjusted to rest of world)
        • Rest of world: 87.5 MHz to 108 MHz
      • Application Mode: Sweep Averaged

    4. Setup PLL for tracking
      • In Lock-In Tab, set Demod 2 to 200kHz bandwidth
      • In PLL Tab:
        • Set Input to Demod 2
        • Set Output to Osc 1
        • Set Center to radio station frequency from Sweeper
        • Set Upper Limit to 100 kHz and Lower Limit -100 kHz
        • Enter 80 kHz in the Advisor and click Advise, the click To PLL
        • Enable PLL


  1. Setup sound output (dF of PLL) on Aux Output
    • Select PID 1 as output
    • 1 µV/Hz yields healthy sound volume
    • Connect a pair of head phones to the Auxiliary Output of the UHFLI Lock-in Amplifier

Happy listening!