Dynamic Carrier Control
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All modern high power (power > 50 kw) shortwave transmitters incorporate Dynamic Carrier Control (DCC) of some kind.
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[edit] History
This Amplitude Modulation (and vestigal SSB) modulation energy saving mode was devised in the late 1930s. DCC was not implemented in transmitter designs until the 1980s, because of some of the complexities of the control circuit.
- DCC's appearance is linked to NATO nations trying to save energy as a result 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 universally mandated by those purchasing the shortwave transmitters.
- Eastern European manufacturers of shortwave transmitters never adopted DCC because Russia in particular had no energy crises due to its abundant supply of oil.
[edit] 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 electricity.
- 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 receiver to remain locked to the carrier.
- DCC can work with Frequency Modulation (FM), but was never adopted for high power FM stereo transmission.
[edit] Operational usage
When running a transmitter with DCC, these settings are recommended to optimize power savings versus listener's receiver signal lock loss.
- DCC (Attack, Decay) : Instantaneous
- DCC (Carrier power suppression): 3db (for 3rd hop targets)
- DCC (Carrier power suppression): 6db (for 1st hop targets)
Occasional misuses of DCC
- Radio NZ International due to long term funding problems has had to resort to using 6db of carrier suppression, making reception in North America difficult.
- DCC can make DXing SW signals more difficult.
[edit] Transmitters using DCC
Here is a list of manufacturers that offer DCC in their shortwave transmitters
- RIZ Zagreb
- Thales
- Telefunken
- Continetal
[edit] Technological obsolescence
Digital 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.
