Broadcasting FM and AM Radio with the Zurich Instruments UHFLI 600 MHz Lock-in Amplifier

Following my previous blog, Listening to FM Radio with the UHFLI 600 MHz Lock-in Amplifier and PLL, people advised me to also try and broadcast FM Radio. Naturally for this I had to retreat into Zurich Instruments’ shielded radiation lab, so that my trials would remain concealed. It then took about 5 minutes to broadcast tunes from my mobile phone 3.5 mm jack using the UHFLI Lock-in Amplifier. Here is what the setup looks like:

ZI_UHFLI_Lock-in_Amplifier_FM_broadcast_setup

The procedure to setup everything is the following.

  1. Connect the mobile phone to the UHFLI Signal Input 1 using a 3.5mm-jack-to-BNC cable
    3.5 mm jack to BNC
    3.5 mm jack to BNC
  2. Connect the antenna cable to Signal Output 1Radio antenna

    The radio antenna. Cable should be on the order of 1m length.

  3. Configure Demodulator 1 to capture the audio signal (yes, this is a hack – but it does perform)
    • Frequency 0 Hz
    • Bandwidth 30 kHz
  4. Configure the Signal Output
    • Setup Demodulator 2 as the signal generator
    • Select Osc 2
    • Set output amplitude to 1V, disable all other outputs
    • Enable Signal Output 2
  5. Configure PID to modulate Osc 2
    • Set Input to Demodulator X, 1
    • Set Output to Osc 2
    • Set Setpoint to 0 V
    • Set P=300 kHz/V, I=0, D=0
    • Set Center to 106 MHz
    • Set Limits to +-500 kHz
    • Enable PID

The nice thing is that you can actually tune your broadcast station to your radio!

Zurich Instruments UHFLI Lock-in Amplifier GUI

(Click to enlarge) The plotter shows the frequency shift of Oscillator 2, which encodes the audio signal.

In order to do the same with AM, you need to set set Osc 2 to 106 MHz and to adjust the PID configuration

  • Set Input to Demodulator X, 1
  • Set output to Output 1 Amplitude, Amplitude 2
  • Set Center to 0.5 V
  • Set Limits to ±0.5 V