Perhaps I'm just an old dog, but while learning the new tricks of HD Radio the one thing that always seems to be missing is a high quality instrument for listening to the demodulated digital signal. We've been forced to make use of the currently available HD Radio receivers, and although they're OK to listen to, I never really expected the greatest sound out of an inexpensive consumer-grade radio. Adding HD2 just made the situation more complicated.
Performance at a glance
Synthesized, push-button tuning
High-level or antenna-level RF inputs
Balanced, line level outputs (Phoenix connectors)
HD Radio to analog time-alignment monitor
Transformer-isolated S/PDIF digital output
Bright LED bar graph metering
When I was offered the opportunity to look at the Day Sequerra M2.0 modulation monitor I eagerly took it.
The mod monitor is a 2RU, full-featured receiver that provides LED bar graph metering for analog, HD Radio and multicast modulation. The unit includes balanced, line level outputs, a S/PDIF digital out and a front-panel headphone jack. These are all features that those of us who grew up with analog radio became accustomed to (and I kind of felt lost without).
The unit is designed and constructed in a way that will keep it from becoming obsolete any time soon: the receiver, the audio section, the CPU and even the power supply are modular. The firmware updates via flash programming memory.
The most striking visual feature of the unit itself is the blue LED bar graph used to display the demodulated HD levels. It's unlike anything I've seen before, and it's a cool feature to go along with new broadcast technology. The unit also includes a vacuum-fluorescent display that provides tuner status, frequency and all the HD Program Specific Data (PSD) information--station name, title, artist, album, genre, program type and comments--for the HD Radio MPS and SPS.
The digital audio output is derived using a low-jitter D/A converter with an inherent THD of less than 0.005 percent. The channel separation for the demodulated digital output is rated at greater than 90dB.
A couple of options are available for the M2.0. Option M2.1 adds measurement capability in the analog domain: 19kHz pilot, 38kHz, as well as 57kHz, 67kHz and 92kHz subcarriers. There is a front-panel metering position for synchronous AM noise, along with a rear panel composite output for driving subcarrier decoders.
Option M2.2 includes the Day Sequerra Remote Dashboard software, a proprietary PC-based application, and an Ethernet interface to provide remote control monitoring for AM and FM HD Radio broadcasts and an alarm panel for HD Radio signal and data attributes.
Another option for the system is the Performance Loss Module, which has several interesting and useful features. It will generate alarms (that can be assigned to dry-contact relay closures available on rear-panel connectors) that correspond to loss of common HD Radio attributes such as MPS audio, multicast audio, analog audio, RF signal strength and loss of OFDM lock.
The unit is exceptionally easy to install and use because it's much like any other modulation meter you've seen or used. Place it in a rack, connect an antenna to it (75Ω input, type F connector) and it's ready to play. Select the desired band, then use the up and down buttons to tune up and down the dial. Once a station is tuned, the unit decodes the analog audio and displays it on the lower LED bar graph set. If the station broadcasts in HD Radio, two things quickly happen. If a multicast is present the front panel blue LED "multicast" LED illuminates. Shortly after that, another small blue LED indicator showing "HD Locked" will illuminate, and the demodulated audio will quickly fade from the analog to the HD1. In the presence of the multicast, press the "mode/service" button, which will switch the audio output to the HD2 stream immediately. If there is an HD3 signal, simply pressing the "up" button will cause the receiver to switch the audio output over to that. Press "down" to go back to HD2, and mode/service to go back to HD1.
Toggling the "data-display" button allows you to read all the fields that are available for PSD. This is obviously a quick way to check that your data is correct and is displaying what you want.
The best thing about the M2.0 though, is the way it sounds. Now you can really hear just how good your HDRadio audio can sound after all--you'll be pleasantly surprised. In fact you may be shocked. Being able to go back and forth easily between different HD Radio streams is educational in terms of processing--nice if you happen to be using two different processors, too. And being able to quickly study your competition's HD Radio audio -- now that's what radio engineering is all about.
Irwin is director of engineering at Clear Channel, Seattle.
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