Mod Monitors Special Report: Grant
In the final part in our special series on tech trends
in modulation monitor design, we query Mark Grant, design engineer at Belar
Electronics Laboratory Inc.
have mod monitors changed notably in the past five to 10 years?
HD Radio has been the biggest change in our focus over the last 10 years. Designing
equipment to monitor the HD portion of the signal while at the same time
providing the broadcaster with accurate analog measurements has been the
challenge. The complexity of the monitor has increased considerably as a result
of this change.
As far as the technology, we have
moved away from alphanumeric, seven-segment and LED indicators on front panels
to high-resolution graphical displays. This provides flexibility in how
information is presented and features can be added or modified with software
The internal processing of the monitor has also
evolved to direct RF carrier sampling with down conversion, demodulation and
measurements, all software-based.
what direction are they heading next?
Grant: The next generation of modulation
monitor will be a general-purpose hardware and display platform with software-defined
functionality. The term software-defined radio comes to mind, but instead think
software-defined modulation monitor.
In addition to the ability to monitor standard analog
AM, FM and shortwave signals, future monitors will also need to be able to
monitor HD Radio, DRM, DAB and whatever else comes down the pike. This will
require a monitor with a flexible wide-band RF input and lots of internal
processing and display power.
unique problems are generated by HD Radio, when it comes to monitoring and
Our standard analog monitors were designed with maximum bandwidth in order to
pass the analog signal transparently. HD requires reduced bandwidths; this
results in a compromise especially for total modulation readings. The HD
carriers and analog FM sidebands overlap in the frequency range above +/- 100
kHz. When this portion of the spectrum passes through an FM demod,
self-interference results, as David Hershberger has written in Radio World. When
separate analog and HD transmitters are used, the analog TX sample can be feed
to the analog monitor, but where a combined hybrid signal is fed to the monitor,
internal filtering is the only option. The FMCS-1 uses a combination of
selectable RF filtering to suppress the HD carriers, variable bandwidth
composite filtering and peak weighting to achieve accurate total readings.
about for RDS?
From a monitoring point of view, RDS is stable and mature technology without
any major issues.
industry discussion about Single Side Band Suppressed Carrier affect your
Grant: Our current FMCS-1 and FMHD-1
monitor’s stereo decoder is software-based and could take advantage of the
reduced L–R bandwidth of the SSBSC signal. Currently both monitors decode the
full 23–53 kHz L–R frequency range, but filtering to 38 kHz could be
implemented in software. The monitor could also provide the ability to A/B
compare the audio using the full and reduced bandwidth L–R signal.
is the next big challenge facing mod monitor designers?
Adapting to all the emerging digital transmission standards.
what is your newest or most notable product in this segment?
Grant: The latest addition to the
FMHD-1 is a decoder expansion board that allows up to four HD streams to be
monitored simultaneously. Also, customers using the FMHD-1 and FMCS-1, please
check our website for software updates periodically at www.belar.com/update/index.html.