Once an HD Radio system is operating in a stable fashion, the various parameters and data streams associated with the MPS and the SPS (and perhaps even another SPS) must be monitored. It used to be that all a station really needed to do was watch the peak modulation level, and in addition with FM, the pilot level and once in a while the L-R level (for the occasional out-of-phase song). Now with HD Radio, it's important to monitor and measure the time alignment and level alignment between the analog modulation and the MPS, and stations will likely want to monitor the RBDS on the analog channel along with PAD data for both the MPS and SPS. Fortunately, there are now multiple monitoring devices made specifically for HD Radio, and each of these devices gives the end user options about which parameters are to be measured, and how the device is to alert the user once a problem is detected. Do you want a contact closure to signal your legacy remote control? Or do you want an e-mail about an out-of-tolerance parameter? Want to browse into the monitor itself via the Internet? Well then, you're in luck: That's a common feature now.
Here's a rundown of several major monitoring products available today.
Belar Electronics offers the FMHD-1, a combination analog and HD Radio monitoring system. This radio has three antenna inputs: one for off-air reception, and another group of two to be used while the device is located at the transmitter site. One input of that group is used for high-level RF from an analog transmitter, the other is used for high-level RF from the HD Radio transmitter. The monitor receives and demodulates the analog and digital signals simultaneously, displaying them on a 640 × 240 color LCD display. (A rotary knob/encoder completes the basic user interface.) The display is used to show HD Radio status, data, time alignment, and configuration information; for the analog transmission, it displays total modulation, pilot, L, R, L+R and L-R. Additionally, the display can be used to show a spectrum of the analog and digital signals.
The time alignment scales are ±375ms (±16384 samples) and ±5.8ms (±256 samples).
The FMHD-1 has eight user-assignable audio outputs on its rear apron that can accommodate the analog versions of the FM signal plus the MPS, SPS1 and an SPS2. The unit also has three user-assignable AES-3ID outputs (75Ω unbalanced). There are two demodulated composite outputs and two LVDS outputs (RJ-45, 100Ω).
This monitor can be controlled by a computer via its Ethernet capability or the RS-232 serial connector. Wizard for Windows is the Belar software that allows the user to remotely monitor the FMHD-1. And finally, there are four user-assignable relay contacts to indicate alarm conditions.
Audemat-Aztec offers three different versions of its HD radio monitoring system: the Goldeneagle HD FM, the Goldeneagle HD AM, and the Goldeneagle HD FM/AM.
Audemat-Aztec Golden Eagle AM/FM monitor
These units will constantly monitor a station's (or stations') parameters and generate alarms should any of the selected parameters fall outside their pre-programmed tolerances. The unit will display all RBDS and PAD for HD Radio. It has an embedded Web server (used with client software supplied by Audemat) to study the detected parameters from afar via the monitor's Ethernet capability. Another feature of the Web server is that of streaming audio: The end-user can listen to a stream of embedded left and right audio, or alternately, the left channel can be a stream of the analog audio while the right channel is a stream of the digital audio. This obviously facilitates the time alignment adjustment. Of course if you are in the same room with the unit, the audio is available on a headphone jack, or via balanced analog audio, or a balanced AES version.
Alarms are reported via e-mail or optionally by voice or contact closures that signal an in-place remote control.
An optional FFT spectrum analyzer module enables the end-user to see the real-time spectrum of the complete RF signal. Thresholds can be set with respect to a spectrum mask so out-of-tolerance conditions can be detected and reported. With the spectrum analyzer option comes what Audemat refers to as the Digital Demodulator, which provides representation of total modulation, pilot and RBDS injection, and the analog and digital levels displayed in a bargraph format.
Day Sequerra has a wide line of HD Radio monitoring products such as the M4.2R (an updated version of the M4). This monitor will tune both AM and FM bands and has the capability of storing up to 20 presets. It will detect and display RBDS data (Program Service and Radio text fields) for the analog modulation, plus PAD data (station long and short name, program type, song file, artist, album, genre and comment fields) for each HD channel.
Day Sequerra M4.2R monitor
It has six alarm relay contacts that can be assigned to represent loss of RF carrier, audio, OFDM, RBDS, PAD, multicast or time alignment. These same alarms can be reported to the end-user via e-mail. Day Sequerra's remote control software is called Remote Dashboard and communicates with the M4.2R via its Ethernet port. There again, if you are in the same location as the monitor itself, you can listen to the demodulated signals via the front headphone jack or via balanced analog (+4dBU) outputs on the back. A transformer-isolated 110Ω source SP/DIF digital output comes from a rear-apron XLR-type connector.