Re: [IRCA] [NRC-AM] IBOC vs MDCL

[Doug Smith <w9wi@xxxxxxxxxxxxx>]

Patrick Martin wrote:
> I have heard that 710 LA has shut off their IBOC for something called
> MDCL? Any idea what that is and does it cause sideband hash like IBOC?

MDCL = "Modulation Dependent Carrier Level".  No, it doesn't cause sideband hash; arguably it might be *better* for DXers than ordinary analog AM.


In normal AM, the transmitter must provide enough carrier to support the modulation.  Not enough carrier, and you get distortion -- "overmodulation".

During quiet passages, when the audio is lower, you don't need as much carrier.  But traditional transmitters provide that unnecessary extra carrier 
anyway.

In MDCL, the carrier level depends on the modulation level.  When the audio is lower & you don't need as much carrier, you don't provide as much.  The 
energy in that carrier comes from the power supply -- which comes from power provided by the electric utility -- which charges for that power.  Use 
less carrier, and you pay a smaller electric bill.  That's the point of MDCL.


Hams who remember something called "Controlled Carrier" may recognize the idea.

It is obviously more complex than regular AM, though with modern software-driven transmitters, maybe not as complex as one might think.  From what I 
read it's also susceptible to being noisier during quiet passages.  (when the weaker carrier causes the receiver's AGC to bring up the gain -- and 
with it any noise)

--

Doug Smith W9WI
Pleasant View, TN  EM66
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