Harris Flexiva Raises HD Radio Sidebands
Ohio — Dayton Public Radio is a CPB-qualified nonprofit corporation and
licensee of two noncommercial FM stations, WDPR(FM) and WDPG(FM). Dayton Public
Radio provides the only classical music and fine arts programming to more than
1.1 million listeners in west central Ohio, including the Dayton metro
(Arbitron market #63). JMS & Associates, with 30 years of experience in
designing, building and maintaining state-of-the-art broadcast facilities, was
retained by Dayton Public Radio to handle its technical requirements including
Classical music audiences are critical
of program audio quality, so WDPR became an early adopter of IBOC HD Radio in
2004 with the installation of a Harris Z6HD transmitter and Dexstar exciter. I
later converted sister station WDPG to IBOC with a split-level system using
their existing Harris HT-20 and a Harris Z8HD+. DPR also upgraded to
accommodate multicasting and enhanced data capabilities.
As the initial –20 dBc IBOC levels have
proven to not yield coverage parity with the FM analog signal, I closely
followed the research and testing regarding elevated IBOC sideband levels being
done by John Kean and NPR Labs, as well as CBS, Clear Channel and Greater
It appeared that an IBOC level of –14
dBc was a good compromise for improved IBOC coverage with tolerable levels of
interference to the analog signal. The Corporation for Public Broadcasting
began offering grants for stations to convert to IBOC HD Radio or improve
existing facilities, so I began researching a solution.
WDPG is a 50 kW Class B with a TPO of
12 kW. WDPG utilizes a directional antenna on a leased tower, so combining was
eliminated as a reasonable option, as was high-level combining due to the high
cost and inefficiency.
The initial split-level system that was
implemented for an IBOC level of –20 dBc, which worked quite well at that
level, could not adapt to IBOC levels higher than about –18 dBc due to mask
compliance challenges. Low-level combining seemed plausible, but there were other
limitations at the site.
Space was limited in the existing
prefab concrete shelter, and I wanted to maintain the existing HT-20 as an
analog only auxiliary. The shelter could accommodate only a six-ton, wall-mounted
HVAC unit for the closed system, so heat load and efficiency were factors.
Reliability is always important and I wanted to avoid a tube-type transmitter
to minimize site visits and lower ongoing costs.
The ideal solution would be an
efficient solid-state transmitter with great performance, multiple layers of
redundancy, a small footprint and compatible with existing station equipment. I
spent considerable time researching new and existing products from the major
transmitter manufacturers and queried other station engineers.
My search ultimately led to the Harris
Flexiva FAX-20 transmitter. I was familiar with the LDMOS-FET technology that
Harris uses in Maxiva solid-state TV transmitters, which allowed a very
high-power density in a small physical package. This technology found its way into
the radio line with Flexiva. The 20 kW model has a smaller footprint than the
Z8HD+ it would replace. Space problem solved.
Each power amplifier has its own power
supply for 1:1 redundancy, and the transmitter will run with several failed
amplifiers. When a PA or PS fails, they are hot-swappable, minimizing downtime.
There are redundant fans as well. The FAX-20 is actually two combined 10 kW PA
blocks (which I fed via two separate AC power feeds), so an entire PA could
fail and the station would still be on the air at reduced power. Automatic
restart eliminates another potential issue.
The transmitter includes a FlexStar
HDXexciter, which delivers a high-quality signal. It has grown in reliability
since our first HD installation in 2004, when iBiquity was still working on the
right coding recipe.
Another important feature is the Harris
Real Time Adaptive Correction software, which maintains FCC spectral mask
compliance despite varying conditions and the elevated IBOC levels. Changing
modes between FM, FM+HD, and HD only, or changing the IBOC injection level from
–20 dBc to –14 dBc is as simple as changing a data field. The Flexiva
amplifiers change bias on-the-fly to maintain linearity and optimum efficiency
for the respective mode.
Installation was straightforward. We
slid the PAs and PSes into their slots and the exciter into its rails, and
installed the 3-1/8-inch RF line to the antenna switch (with a Bird BPM power
meter in line). Following electrical and grounding work, we connected the AES
audio and exporter LAN from the Harris Intraplex STL and tested into the dummy
load. The transmitter had been tested and burned in at Harris, so the initial
turn-on consisted of depressing the “on” button. Cool!
Interfacing to our Burk Systems remote
control was a breeze since telemetry, status and command logic levels are
standard. The ability to monitor and control the transmitter via a Web-based
browser from anywhere with Internet access provides another layer of
The Flexiva was ready to be put on the
air after upgrading the software and configuring the Harris HDE-200 embedded
exporter and HDI-200 importer. The new embedded exporter solves many of the
problems the earlier models had due to dependency on the computer hard drives
and operating system. The HDE-200 configuration and monitoring is now done via
an administrative computer on the network. No changes were necessary to our
Intraplex STL or other station systems. The Bird BPM power meter, Agilent
spectrum analyzer and Belar FM HD-1 mod monitor verified proper operation.
WDPG is now operating at –14 dBc IBOC
level. Digital coverage has increased with no discernible interference to the
analog signal. So far we have not had a failure or maintenance issue and are very
satisfied with the Flexiva and Harris support.
Stitt is president of JMS & Associates.
For information, contactBrian Clifford
at Harris in Ohio at (513) 459-3714 or visit www.broadcast.harris.com.