Trends in Technology: Monitoring HD Radio

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When I first put an IBOC radio transmitter on the air (almost six years ago) there weren't many good choices in monitor receivers. There were plenty of radios that would pick up the IBOC signals, but none could really be relied upon in the way that we were accustomed to with analog modulation monitors. Fortunately since then, both known and not so well known manufacturers have developed new monitors. These IBOC monitors make great analog FM monitors too, so that's an additional benefit. Here's a look at what's out there.

The company with the longest history in making modulation monitors for broadcast has to be Belar Electronics. Its IBOC monitor is the FMHD-1. Some of its most important features are:

  • Frequency agility
  • Off-air reception or high-level inputs available
  • Metering of IBOC L, R, L+R and L-R
  • Metering of analog L, R, L+R, L-R, pilot, and total mod
  • Time and level alignment (analog vs. IBOC audio)
  • Spectrum analysis
  • SIS and PSD data
  • IBOC status and control information
  • Bit error rate measurement
  • Four user-assignable alarm outputs (via relays)

    The FMHD-1 actually has two high-level RF inputs available, so if it is installed at the transmitter site using separate transmitters for analog and IBOC, the RF signals can be combined within the meter itself. It also has two modes of communication available: Ethernet and RS-232. In either case, Belar's GUI -- WizWin -- must be installed to access the unit. The monitor also contains two IBOC decoders; so two streams can be decoded simultaneously.

    The FMHD-1 is 2RU and has a 640X240 LCD color display on the front panel along with a rotary encoder wheel used to control and configure the unit.

    I want to point out two of the displays that I think are most useful to those that transmit IBOC signals. The first (Figure 1) is the time and level alignment.

    This visual representation is handy primarily because a lot of information is gathered all in one spot. Note though that the range on the delay is +/-372ms, so before you got to this screen, you would need to rough-in the time delay to something much less. Based on my experience, time delay needs to be checked fairly frequently.

    Figure 1. Time and level alignment screen on the Belar FMHD-1

    Figure 1. Time and level alignment screen on the Belar FMHD-1

    PSD also needs to be checked regularly. The FMHD-1 has a display to help with that (Figure 2).

    And I mentioned that the newer IBOC monitors have useful features for the analog transmission as well. Figure 3 shows the display for analog levels.

    Figure 2. The FHMD-1 PSD parameter display

    Figure 2. The FHMD-1 PSD parameter display

    Of course on the legacy analog meters, you can select the desired parameter to monitor and show the results one at a time via pushbutton. Having a visual display such as this is quite useful.

    Figure 3. Analog readings can also be made with the FMHD-1.

    Figure 3. Analog readings can also be made with the FMHD-1.

    -- continued on page 2

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