Re: [IRCA] IBOC power

[Barry McLarnon <bdm@xxxxxxxxxx>]

On Friday 23 September 2005 17:53, Dan Strassberg wrote:
> Several posters have mentioned incorrect powers for the MW HD Radio
> digital sidebands. My understanding is that the combined power in the
> two digital sidebands is not supposed to exceed 1/16 (6.25%) of the
> nominal power of the analog carrier. Each digital sideband is allocated
> half of the total digital-sideband power or 1/32 (3.125%) of the nominal
> analog-carrier power. As someone else stated, each sideband contains
> multiple carriers, each carrying 16-QAM modulation. The envelope
> detectors used in most AM receivers apparently make this form of
> modulation sound a lot louder than you would expect based on the
> relatively low digital-sideband power. I think the exaggerated loudness
> occurs because the modulation index of the digital sidebands is much
> higher than the average modulation index of the amplitude modulation on
> the main carrier. In analog AM, the sideband power is variable and more
> power goes into the analog sidebands as the signal gets louder. I
> believe that QAM (like FM) is a form of modulation in which the sideband
> power is constant (and therefore always maximum). If anything I've said
> in this message is incorrect, please set me straight.

Well, you need to differentiate between the different digital sidebands, 
which have different power levels and different modulation types (not all 
16QAM).  For the real skinny on this, see my page at
http://topazdesigns.com/iboc/AM-IBOC-Parameters.html

Barry

-- 
Barry McLarnon VE3JF  Ottawa, ON

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