Frequency Bands

If you do a search on the origin of the designations for the various frequency bands, what you  will find is that nobody really knows. I have seen some pretty bogus explanations for how the band designation came to be, but I seriously doubt that the letters were assigned in order to confuse the enemy during WWII, or that "X" band was named for "cross," like in the cross hairs of precision targeting radars.

There is some logic in the upper and lower frequencies of the bands, however. The "3x10^n" frequencies derive from wavelength in meters. Recalling that the speed of light in air is 300,000 km/s, that means a 1 meter wavelength translates to a frequency of 300 MHz, 10 meters is 30 MHz, 100 meters is 3 MHz, etc.

At some point, some wise soul decided that it was time to start over at a single digit for L-band at 1 GHz. The new regions are in octaves, except for 3 GHz, up to 8 GHz. If anyone knows why 12.5, 18, and 26.5 GHz band edges were chosen, I would appreciate your letting me know. 

Regarding the Ku, K, and Ka bands, supposedly K was named after the German word for "short," as in shortwave - Kurz. Ku is supposedly for K-under and Ka is supposedly K-above. That, of course, is inconsistent since since the K, if is derives from Kurz in wavelength, so K-under would be a lower (lesser) wavelength (hence higher frequency) and K-above would be a longer (greater) wavelength (hence lower frequency). Mostly likely, the certain origins are buried with their progenitors.

This chart shows the relative positions of the most common frequency bands, and is not to scale. 

30 Hz     300 Hz     3 kHz    30 kHz        300 kHz    3 MHz      30 MHz      300 MHz       1 GHz     2 GHz     3 GHz     4 GHz     8 GHz     12.5 GHz       18 GHz     26.5 GHz       30 GHz       40 GHz      300 GHz         >300 GHz         
ELF                                    
  VF
  VLF
  LF
  MF
  HF
  VHF
  UHF
  L-Band  
  S-Band
  SHF
  C-Band        
  X-Band
  Ku
  K
  Ka
  EHF
  Millimeter
ELF    = Extremely Low Frequency
VF      = Voice Frequency
VLF    = Very Low Frequency
LF      = Low Frequency
MF     = Medium Frequency
HF     = High Frequency
VHF   = Very High Frequency
UHF   = Ultra High Frequency
SHF   = Super High Frequency
EHF   = Extremely High Frequency
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