SEATTLE — HD Radio diversity delay has been a much-discussed topic in the industry over the past 12 months. We’ve finally reached a point where manufacturers are announcing products and solutions to time-align analog FM and HD broadcasts.
I’ve had a look at some of the different systems in the market, all of which have interesting benefits. To date, however, it seems to me that Belar is delivering a product with the best set of tools and functions.
I’ve been using Belar Electronics modulation monitors since joining the industry 30 years ago. Belar has always offered reliable products, and our early experiences with its Automatic Delay Correction software follow that same path.
DRIFT CORRECTION
Built into the Belar FMHD-1 mod monitor, Automatic Delay Correction gives broadcasters the option to correct signal drift through connectivity with an HD Exporter, audio processor or separate delay line. We have installed the software at two sites for KQMV(FM), serving the Puget Sound region of Washington state. Our main transmitter site is on Tiger Mountain, where the software communicates with a Nautel exporter; and our backup site resides on Cougar Mountain, where the architecture employs an Omnia .9 audio processor.
At the Tiger Mountain site, the Nautel exporter adjusts the delay on the HD audio signal by looping the HD audio feed through the analog delay line in the exporter. This allows us to run a constant delay in the audio processor on the analog composite while adjusting the delay on the HD audio side. On Cougar Mountain, all delay exists in the audio processor on the analog audio path. The software is working well at both sites.
Diversity delay has been such a hot topic because the signal between analog and HD can drift almost anywhere within the coverage area. This is due to a drop in signal strength, which commonly happens between buildings, driving through tunnels or in fringe coverage areas. When signal strength drops, the HD broadcast should blend into the analog signal. If not time-aligned, listeners experience an unpleasant stuttering effect due to variances of the typical eight-second delay between HD and analog feeds.
The connectivity between Belar and our exporter and processor makes it easy to solve this problem.
Since the software is so new, we worked with the Belar team to configure the system. Setup was fairly simple. Upon launching the software, the first step is to enter the IP address of the component being controlled (exporter, processor, delay line). The software immediately begins adjusting the time delay based on what the monitor is receiving off air. The software interprets the signal characteristics, adjusts the component upstream and feeds the correction. This happens in a continuous loop to ensure consistency.
The software delivers dynamic visual displays on the monitor window. There are a few key indicators to watch. At the top of the window, a yellow bar indicates signal loudness. At the bottom, a second yellow bar shows the time alignment, with activity to the left conveying “analog lagging,” and movement to the right communicating that the analog signal is leading.
A red bar above the yellow time alignment bar rests at zero, if everything is in sync; if it moves left or right, the system will automatically adjust to compensate for the discrepancy and return the value to zero. Manual corrections are also possible via the front panel, if desired.
There are some more enhancements on the way. A significant challenge to delay correction is that the signal often drifts outside the traditional correction window. This means that the visual display cannot be used. Belar intends to expand this time window to ensure users can visually comprehend the drift beyond several seconds.
Belar is additionally working on a multisync scanning function that can loop between six stations and their corresponding delay devices. This will be useful at our Cougar Mountain site, which is also the primary site for KRWM(FM). We will use two separate inputs on the FMHD-1 to serve different RF feeds and frequencies.
I suspect that the overall system will evolve further as we move forward. For the time being, Belar is offering a working technology that makes it easier for engineers to keep track of diversity delay. It’s one less problem to worry about.
For information, contact Mark Grant at Belar Electronics in Pennsylvania at (610) 687-5550 or visit www.belar.com.
