Has anyone else noticed WBZ's unlistenable signal

Garrett Wollman wollman@khavrinen.lcs.mit.edu
Tue Jan 18 16:43:05 EST 2005

<<On Tue, 18 Jan 2005 16:35:38 -0500 (EST), Stephanie Weil <sven@gordsven.com> said:

> On Tue, 18 Jan 2005, Garrett Wollman wrote:
>> The IBOC sidebands are transmitted in quadrature, so it's invisible to
>> envelope detectors.  Only people with synchronous detectors hear it.

> English please?  And what radios have "envelope detectors"?

Almost all radios have envelope detectors (or some variation

The IBOC sidebands are transmitted 180 degrees out-of-phase,
superimposed on the upper and lower analog sidebands of an AM
station.  An envelope detector will sum the two sidebands, cancelling
out the IBOC; a synchronous detector in most cases is tuned to only
one sideband (doesn't have to be, but that's the normal application
seen in, e.g., the Sony ICF-2010).


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