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Re: [IRCA] AM vs MW-IBOC range differences
- Subject: Re: [IRCA] AM vs MW-IBOC range differences
- From: Barry McLarnon <bdm@xxxxxxxxxx>
- Date: Sun, 18 Sep 2005 23:36:37 -0400
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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