The effect of HD Radio interference on an analog FM signal

For the past few days, local 96.3 WHUR Washington, DC’s HD Radio signal, which airs on 96.1 and 96.5, has been off-air.  Usually, 96.1 and 96.5 are extremely difficult to DX since WHUR’s digital sidebands are strong at my Northern Virginia home.  However, with WHUR-HD turned off, both of its adjacent frequencies were open to distant reception like they were prior to 2006 when HD Radio debuted on WHUR.  At 8:50 PM February 8, WHUR’s IBOC sidebands resumed its broadcast.

whur_iboc
The above chart shows a waveform of 96.5 FM from 8:49-8:50 PM February 8.  In the beginning, you can see a fairly strong analog signal from 96.5 WKLR Ft. Lee, VA, 92 miles away.  At the 0:05:00 mark, WKLR’s signal decreases as WHUR’s HD revs back up.  at 0:09:50, WHUR’s 96.5 digital sideband is at full-power, and WKLR abruptly disappears without a trace.

Listen to the corresponding audio file to the graphic above.

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