Listening to FM Radio with the UHFLI

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

The procedure is quite straightforward. 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 headphone with 1 uV/Hz, for example. This yields a high-fidelity, crystal-clear mono sound. Here is how it works step by step:

1. Connect an unshielded wire of ~0.75 m length to Signal Input 1.
2. Start the UHFLI in default config (Signal Input 1: 50 ohm, 1 V range).
3. Sweep for radio stations:
   • Points: ~600
   • Log: off
   • Frequency sweep range:
     • Japan: 76 MHz to 90 MHz
     • Eastern 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. Set up the PLL for tracking.
   • In the Lock-In Tab, set Demod 2 to 200 kHz 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, then click To PLL
     • Enable PLL
5. Setup the sound output (dF of PLL) on Aux Output.
   • Select PID 1 as output
   • 1 µV/Hz yields healthy sound volume
   • Connect headphones to Auxiliary Output of UHFLI

Happy listening!