|
FM
Digital Power Increase Needed Because “Coverage is Critical”
One
of the most popular technical sessions at the 2008 NAB Radio Show,
held this past September in Austin, TX, was the “High Power
IBOC Technical Panel” moderated by Geoff Mendenhall, Vice
President, Transmission Research & Technology, Harris Broadcast
Systems. The discussions held during this panel take on new significance
given the FCC’s recent Public Notice regarding the proposed
FM digital power increase, comments on which are due Friday, November
28, 2008 (see below for more information on the Public Notice
and how to file comments).
Milford
Smith, Vice President, Engineering, Greater Media, Inc. gave one
of the presentations in this session, entitled “HD Radio
IS Radio in the New Millennium.” Mr. Smith has overseen conversion
of over 20 Greater Media stations to digital, and served as chair
of the National Radio System Committee’s (NRSC’s) Digital
Radio Broadcasting Subcommittee during the time of the NRSC’s
evaluation and ultimate standardization of the iBiquity HD Radio
in-band/on-channel (IBOC) digital radio system. Mr. Smith assumed
chairmanship of the full NRSC in April 2007 following the retirement
of long-time chair Charlie Morgan of Susquehanna Radio.
The
theme of Mr. Smith’s presentation was that coverage is critical,
and that for the HD Radio transition to be successful, HD Radio
coverage must replicate (or improve upon) the coverage currently
afforded by a station’s analog FM signal. Mr. Smith believes
that the current proposal to allow FM stations to increase their
digital power by up to 10 dB will achieve this, and that broadcasters
must be allowed to move as quickly as possible to implement this
voluntary increase. As a participant in the high power FM testing
done by iBiquity (and submitted to the FCC in June 2008—see
the June
16, 2008 issue of Radio TechCheck for more information
on the iBiquity test report), he is very familiar with the results
of this testing, and during his presentation he summarized some
of these results including the following:
- NO observed
additional interference to the host stations;
- Coverage
improvements were spectacular; in virtually every case analog
coverage was replicated and HD “dropouts” within
that area were close to nonexistent;
- Actual
observed increased interference to first-adjacent channel
stations was minimal and fell largely outside of the
 stations’
protected contours;
- Several
stations operated with elevated digital power levels for many
months (some for more than a year), and at least one is still
operating;
- There
have been NO interference complaints whatsoever from any first
adjacent station, including those short spaced to the high
power operations;
- There
have been NO listener complaints whatsoever.
Mr.
Smith noted that while reliable analog coverage, in most cases,
extends to (or beyond) the 60, 57 or 54 dBu contour (depending
on the class of station), a consensus of knowledgeable group engineers,
backed by several years of actual field observations, indicate
that, in general, reliable HD Radio coverage extends to approximately
the 65 dBu contour of a typical station. He said that in many
markets this abbreviated coverage makes in-car listening over
a typical commute problematical if not impossible.
One
example he gave of this was from the Boston area where drivers
on I-495 (see map), a major commuter artery which circles the
metro, are treated to intermittent digital service from Greater
Media station WMJX. This is because I-495 falls on, or is outside
of, the 65 dBu contour of WMJX which for that station represents
the extent of the digital signal’s coverage. He pointed out
that listeners who purchase their first HD Radio receiver and
experience poor digital coverage will be disappointed and further
noted that in particular, good coverage is critical for the popular
multicast stations (i.e. HD-2, HD-3) which have no analog backup
signal (as do the main channel audio signals). His recommended
plan for moving forward is to:
- Implement
elevated HD Radio digital power levels immediately on a larger
number of stations, via Special Temporary Authority (STA), to
gain more experience and to showcase the improved digital service;
- Since occasional
cases of increased, unacceptable interference to a few first
adjacent stations are theoretically possible, use this opportunity
to investigate asymmetrical and/or reduced sideband power levels
to mitigate any such occurrences;
- Move RAPIDLY
to universal increased digital power levels, on a voluntary
basis.
Broadcasters
interested in filing comments in response to the FCC’s Public
Notice on the proposed FM digital power increase may obtain a
copy of the Public Notice from the FCC’s web site at http://hraunfoss.fcc.gov/edocs_public/attachmatch/DA-08-2340A1.pdf.
Comments are due on November 28, 2008 and replies are due on January
4, 2009. Comments and replies may be filed electronically by accessing
the Electronic Comment Filing System (ECFS) at www.fcc.gov/cgb/ecfs/.
Filers should follow
the instructions provided on the website for submitting comments,
and should include their full name, U.S. Postal service mailing
address, and the applicable docket number: MM Docket No. 99-325.
Parties may also submit an electronic comment by email—to
get filing instructions, send an e-mail to ecfs@fcc.gov,
and include the words “get form” in the body of the
message. A sample form and instructions will be sent in response.
The November 17, 2008 Radio TechCheck is also
available in an Adobe Acrobat file.
Please
click
here to read the Adobe Acrobat version of Radio TechCheck.
|
