[IRCA] IBOC vulnerabilities

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

With IBOC turned loose, I'm going to take a different tack on some of this
and focus on the actual bandwidth.  There is a requirement that stations'
signals fit within a clearly defined mask.  I wonder how many are truly in
compliance 24/7/365?  If the antenna system changes such as with wet ground,
that may alter things.  Further, I would be willing to bet that many just
barely fit the mask - or may not even be in complete compliance.  If that is
the case, then if a station is found to be interfering, the victim may have
an administrative recourse.  I would hope that Bob Savage considers this.

Next week one of my clients is to have it's yearly RF occupied bandwidth and
spurious signal tests done.  I'll query the fellow who does this about what
he's found, and just what equipment and methods are required to make a case
against an offender.  This house of cards may have a rather well-hidden
vulnerability.  This needs to be examined more closely.

In the past, several types of modulation monitors were built to ensure
compliance with the rules.  Perhaps some enterprising company will create a
similar product to monitor occupied bandwidth of IBOC.  I suppose the best
way to test it would be to use a device like the SDR-IQ and record a part of
the spectrum surrounding the assigned frequency.  In that recording, drop
carrier for a few seconds and do an A/B comparison to see what vanishes.
The change of patterns at sunrise/sunset may provide just that opportunity,
though shorter.

Have any of you with a local IBOC station and a SDR-IQ or other radio
equipped with a spectrum display looked at this?  My SDR-14 has not arrived
yet.

Depending on the intensity of the anti-IBOC crowd, this could get
interesting.  I think much more can be done beyond a barrage of letters that
will be ignored.  And, all that is being done is a passive measurement to
see if a station is complying with the rules.  No different than looking at
their monitoring points.  Speaking of which, I have never seen IBOC
referenced to antenna pattern monitoring points.  I wonder if they are
affected by the addition of the IBOC signals?  If they are increased beyond
limits, then that's another problem.  The most commonly used field intensity
meter isn't so narrowband that it would totally reject +/- 10KHz signals.
And, the precise positioning of a null will be slightly different on those
adjacent frequencies due to a differing phase shift.  Yet another issue..

OK, I'm about six or eight months in advance of my self-imposed one per
month IBOC posts..  I'll shut up now.

Craig Healy
Providence, RI

... Sent at 8:16AM EDT.

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