Spectrum Analyzer


spectrum analyzer input <> DC Block <> SMA to BNC <> DUT
spectrum analyzer input <> DC Block <> DUT

Connect TX to Spectrum Analyzer

TX <in[directional coupler]out><in[dummy load xxW]testing port> <10db attenuator> spectrum analyzer
                         - ?

Max Power: take max input of spectrum analyzer, let's say +20dBm

You can calculate the max power in dBm:

100W = 50dBm
 30W = 44dBm

\[ dBm = 10\times\log_{10}\left(\frac{30W}{0.001W (1mW)}\right) = 44.77dBm \]

Since they are too high related to the +20dBm max input, you can put the required attenuators to get down to 0dBm.

  • 50dBm = -40dB + -10dB, or -50dB
  • 44dBm = -40dB + 4dB
TX 50dBm <> dummy load -40dB <> -10dB <> 0dBm spectrum analyzer

Max Voltage, let's say, maximum 5V in:

30W in volts formula: \[ V = \sqrt{30W \times 50\Omega} = 38.7V \]

The equivalent dBm for the 5V max input of the instrument: \[ dBm = 20\times\log_{10}\left(\frac{5V}{0.224V (224mV = 0dBm)}\right) = 26.9dBm \]

Using 27dB attenuation will do the job.


  • LPC501 Directional Coupler
  • Dummy Load with "testing port"/tap/monitor (-40dB)
  • See references for attenuators, directional couplers, etc.
  • dBm units