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Dynamic carrier control

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All modern high power (power > 50 kw) shortwave transmitters incorporate Dynamic Carrier Control (DCC) of some kind.

History

This Amplitude Modulation (and vestigal SSB) modulation energy saving mode was devised in the late 1930s. DCC was not implimented in transmitter designs until the 1980s, becuase of some of the complexites of the control circuit.

  • DCC's appearance is linked to NATO nations trying to save energy as a rusult of the ripple effects of OPEC related oil supply crisies.
  • DCC is still an option on all shortwave transmitters sold on the open market today, but it is almost univerally madated by those purchasing the shortwave tranmitters.
  • Eastern European manufacturers of shortwave transmitters never adopted DCC becuase Russia in particular had no energy crisies due to its abundant supply of oil.

FAQ

Technical notes on DCC

  • DCC causes the carrier level to be automatically reduced when the audio is very weak or no audio is present.
  • During periods of silence (no audio), the carrier power is reduced by 50%, so the 250 kW transmitter is putting out a carrier of 125 kW during audio pauses. This carrier power reduction saves otherwise wasted electrisity.
  • There is a BBC Mode-DCC that behaves the exact opposite to the DCC as it is described above. BBC World Service and relay stations are the only place where transmitter using the BBC-DCC mode. BBC-DCC is said to work better than plain DCC, as it allows the reciver to remain locked to the carrier.
  • DCC can work with Frequency Modulation (FM), but was never adopted for high power FM stereo transmission.

Operational usage

When running a transmitter with DCC, these settings are recommended to optimize power savings versus listener's reciver signal lock loss.

  • DCC (Attack, Decay) : Instantanious
  • DCC (Carrier power suppression): 3db (for 3rd hop targts)
  • DCC (Carrier power suppression): 6db (for 1st hop targts)

Occasional misuses of DCC

  • Radio NZ International due to long term funding problems has had to resort to using 6db of carrier suppression, making recption in North America difficult.
  • DCC can make DXing SW signals more difficult.

Transmitters using DCC

Here is a list of manufactureres that offer DCC in their shortwave transmitters

  • RIZ Zagreb
  • Thales
  • Telefunken
  • Continetal

Technologial obsolescnce

Digtial Radio Mondiale has made DCC obsolete for digital audio broadcasting via shortwave. The digital DRM signal always has the same power level, thus making DCC moot.

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