Re: [IRCA] AM vs MW-IBOC range differences

[Barry McLarnon <bdm@xxxxxxxxxx>]

On Sunday 18 September 2005 22:29, Scott Fybush wrote:
> >I guess I am still lost. KEX putting out IBOC hash of 625 watts? The
> >hash is S9 here. That it pretty powerful for 625 watts.
>
> Keep in mind that the spectral density of an IBOC signal is very
> different from that of an analog signal. Barry, Chuck or Dan Strassberg
> could all explain it in far more detail than I can (unlike them, I'm
> most definitely NOT an engineer), but the energy in the IBOC signal is
> spread much more evenly across the spectrum, and it varies in level much
> less than an analog signal does. The effect is a signal that appears
> much louder and more annoying on an analog receiver than a corresponding
> analog signal would.

Right, and unlike the AM signal with its carrier, the digital signal does 
not waste a bunch of power in a component that does not cause any audible 
interference.  The best model we have for assessing the interference is 
DRM, since an on-channel primary IBOC sideband is essentially the same as
a co-channel DRM signal.  Tests have shown that to provide equivalent 
protection to co-channel stations, a DRM signal should have an average 
power that is at least 7 dB less than the carrier power of the AM signal 
that it replaces.  Or, we can turn that around and say that a DRM digital 
signal, or a primary IBOC sideband, causes about 7 dB more interference 
than an AM signal with the same power.  So, I would estimate that the 
interference that a 50 kW station like KEX puts on each first adjacent 
channel is roughly equivalent to that of a 5 kW AM station.  Extrapolate 
that to a bunch of stations going IBOC, and that's whole lot of new 
stations dropped into the band, running buzzsaws for audio.

BTW Scott, nice to see you here, and I appreciate your balanced assessment 
of the pros and cons of this technology, though I lean rather heavily to 
the con side myself. :-)

Best,

Barry

-- 
Barry McLarnon VE3JF  Ottawa, ON

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