500MHz spectrum analyzer

This is a spectrum analyzer which I made several years ago. I could observe the frequency element of the signal of 0-500MHz using this. I used the satellite TVRO tuner unit sold cheap in the junk store for 1stLO and 2ndLO. This unit contains VCO of the variable range of 500-1000MHz to change 430-930MHz into 70MHz IF. I am changing the signal of 0-500MHz into 1stIF of 500MHz by sweeping this VCO by the ramp wave OSC. And, I used the IC for the mobile radio of JRC for the logarithm amplifier of 3rdIF. This IC contains the IF amplifier which has the very wonderful logarithm character of 90dB. I input a ramp wave and the output of the log-amplifier to the X-axis and Y-axis of oscilloscope, and make it indicate wave shape. I am using BPF of LC-type for the 3rdIF filter which I decide resolution band width (RBW). RBW is about 300kHz. I tried a crystal filter so that I might make RBW smaller, too. But, I couldn't get a good character with the general filter for FM and one for SSB.


  • 1stIF; 500MHz
    1stMixer; diode-type DBM
    1stIF amplifier; 2SK571 (GaAs-type FET)
  • 2ndIF; 90MHz
    2ndMixer; diode-typ DBM
    2ndIF amplifier; 3SK121 (GaAs-type FET) +2SK125x2 (GG-type AMP)
  • 3rdIF; 10.7MHz
    3rdMixer; diode-type DBM
    3rdIF amplifier; NJM2032A (JRC)
  • Sweep range; 0,20k,50k,100 k,200k,500k,1M,2M,5M,10 M,20M,50M/div
  • Sweep time; 5mS, 10mS, 20mS, 50mS,0.1S /div
  • Resolutional band width; 300kHz
  • Spurious free dynamicrange; about70dB (from -100dB to -30dBm)


Circuit schematics

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