Field Report: Harris Intraplex HD Link

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Harris Intraplex HD Link

The Intraplex HD Link is a 950MHz radio system that passes not only the typical program audio, but also HD Radio traffic between a studio location and a transmitter site. If integrated with an IP return path from the transmitter site back to the studio, the system will pass TCP traffic between the two ends, and it will manage packet routing based on the user configuration and path accessibility. The HD Link has all the features we've come to expect from an STL system, and more.

The first thing I do with a radio system (or any for that matter) that has as much capability as the HD Link is put it on the bench and back-to-back the units. I did this by just putting a dummy load on the transmitter, and a small whip on the back of the receiver. After powering the units, they came right up with all their default settings in place. Read the Quick Start Guide (pages three and four in the manual) so that you can configure the system to meet your requirements. Specifically, you'll need to go to the RF profile and to put the system on the correct frequency; and you'll need to set the RF bandwidth so that it matches the emission designator you used in the license application (for example, 500KD7W for 500kHz of bandwidth).

You may want to change the parameters of the two audio pathways from their defaults. One of the default RF profile settings is "any modulation," which allows the unit to change from 32, to 64, to 128 or even 256 QAM depending upon what you ask the system to do. There is only so much data-handling capability available for a given system bandwidth and it's clear that as you ask for more, the QAM number goes higher. For example: With both audio pathways set for 48kHz sampling/stereo/linear, and with the user-IP bandwidth set for 256kb/s, the system modulation scheme goes up to 256 QAM. Changing audio path two to mono (as one example) immediately changes the modulation scheme to 128 QAM. These parameters have a finite number of choices obviously and the system will prevent you from trying to make changes that don't work. As another example: If I leave audio pathway one at 48kHz sampling/stereo/linear, and change audio pathway two to match that, I find that (at 256 QAM) I can get 320kb/s through on the user-IP link; trying to get more than that results in an invalid error message back from the radio.

Performance at a glance
Analog and digital audio I/O
Two G.722 audio paths available
Two stereo program channels
Linear or Enhanced apt-X audio
Multiple Ethernet links

By the way, all the configuration changes I've suggested so far can be done via the front panel. You can also make all those changes and many others by using the Ethernet interface. That allows me to segue nicely into the next important feature of this radio system: its ability to be integrated with a full-duplex IP network between the transmitter site and the studio site.

- continued on page 2

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