The Radio Astronomy Units table (PDF file or Excel XLSX file) shows dBm, Watts, Volts across 50 ohms, temperature in K/1Hz, dBW and Jansky equivalent values.

This is the first step to convert the Tektronix MDO4104-6 spectrum analyzer data in dBm measurements to other radio astronomy units.

Conversion formulas:

• Power in dBm is the vertical scale of the spectrum trace measured by the spectrum analyzer.
• Watts
  • Watts = POWER(10,dBm/10 -3).
  • 0 dBm = 0.001 Watts or 1 mW.
  • -10 dBm = 0.0001 Watts or 0.1 mW.
  • -60 dBm = 0.000001 Watts or 1 uW.
• Volt (usually in uV) across 50 ohms is used for receiver measurements.
  • Volts across 50 ohms = SQRT(Watts*50).
  • -106 dBm = 1.1 uV across 50 ohms
• Noise temperature in Kelvin.
  • Noise temperature in Kelvin = Watts/1.38E-23/1Hz.
  • 1.8E+9 K = 25.1E-15 W/1.38E-23/1 Hz.
  • Noise temperature is in per bandwidth of 1Hz.
• dBW
  • dBW = 10*LOG(Watts,10) or dBm-30.
  • 0 dBW = 1 Watt = 30 dBm.
  • -106 dBm = -136 dBW = 25.1E-15 Watts
• Jansky (named in honor of Karl G. Jansky, founder of radio astronomy, Electrical Disturbances Apparently of Extraterrestrial Origin).
  • Jy = =POWER(10,(dBW+260)/10)
  • 1 Jy = -260 dBW/1m^2/1Hz = 10E-26 Watts/1m^2/1Hz.
  • -106 dBm = 2.5E+12 Jy/1m^2/1Hz.
  • Jy is in per meter squared and per bandwidth in Hz.
  • Used in Figure 1.6 Jovian flux density as a function of frequency for both Io-related and non-Io-related emissions, in Listening to Jupiter, A Guide for the Amateur Radio Astronomer, Second Edition, by Richard S. Flagg, page 1-6.

© 1998-2014 David Haworth