Dual-Input Antennas Make Transition to HD Radio a Breeze

Alex M. Perchevitch

Making the transition to HD radio need not be a complicated, expensive or as time consuming as many people think. An installation we did recently for Utah Public Radio to inaugurate HD broadcasting for KUSU-FM, a non-commercial station owned by Utah State University illustrates my point. 

KUSU-FM broadcasts to the Salt Lake City area at 91.5 FM and had an analog antenna that was nearly 30-years old. Like many public radio stations they wanted to broadcast HD services in addition to continuing their analog channel. Also, like many public stations they are hard-pressed for cash and must make sure that every dollar invested in new equipment has a long, productive life.  The old antenna was not only nearing the end of its useful life, but mounted on a tower on a windy ridge line northwest of Logan, Utah to maximize coverage of the Salt Lake and Cache Valleys.

Wind load was a problem with the old “Rototiller” style analog antenna.  It was mounted high on its tower, big, with large surface areas susceptible to movement during windy conditions. In addition, the antenna consumed valuable tower space and capacity that could otherwise be used productively.

Our engineers looked at the situation and came up with a simple, cost-effective solution for KUSU that was a win-win from both the tower / transmitter side and the antenna aspects of the installation. It took the form of our new dual-input model JSHD 6-bay antenna. By using its isolated dual-inputs, KUSU could continue to use its analog transmitter and only needed to add a lower-power digital transmitter for the HD signals.  As a result of installing the JSHD, the existing analog transmitter was able to put out a vastly improved analog signal on one antenna input and HD signals on the other isolated input. Now, in addition to a cleaner analog broadcast, the station now has a new simulcast digital broadcast of National Public Radio and Public Radio International, a new HD2 channel of all-classical music and a new HD3 channel that is operated on campus by the Student Radio Club. All resolved with one great antenna design!

Friend Weller, the Chief Engineer at Utah Public Radio paid us a compliment: “Based on the criteria we specified for the amount of gain we wanted, available tower space, delivery schedule and price, Jampro won the contract. We have nothing but good to say about the Jampro engineers.”

Because of the design and high performance of the JSHD, it improved the center of radiation over the old antenna. This allowed both the analog and digital signals to maintain a center line of radiation and ensured the efficiency of all signals. At the same time, the JSHD actually lowered the tower loading, thereby increasing the tower’s capacity to hold more antennas. Tower space is a valuable commodity and can bring in additional revenue for the owner, in this case Utah Public Radio. When you consider that the customer was originally considering building a new tower due to the excessive wind loading problems with the old antenna the JSHD solution was an enormous savings.

We are very proud of our JSHD antenna. It is the culmination of 30-years of Jampro research and field experience with dual-input antennas for FM and TV broadcasters. It can handle input ratings up to 75 kW with ERP ratings to 0.4 MW. The design allows the digital transmitter to operate at target power with no power lost in reject loads and no power reduction caused by lossy digital injectors. Our built-in power distribution system assures reliability because there is no single point failure that can take the antenna totally off the air. The system uses two separate and isolated RF paths so the antenna is fully redundant. Except for power levels, either input can be used for either analog or digital RF. This design permits easy testing of the antenna system, coax and transmitter. The JSHD allows dry air or nitrogen pressurization from the input connectors through to the radiating dipoles to protect the antenna from moisture. KUSU’s antenna is also protected from ice, snow and rain by radomes.

Reports I’ve received on the effectiveness of the analog and digital signals coming from the JSHD have been impressive and exceeded KUSU’s expectations. Jampro’s dual-input solution was ideal for KUSU. It solved several problems at once. It avoided new tower construction, solved a serious wind loading problem, freed up valuable tower space, continued the life of the existing analog transmitter, improved analog transmission and added several new, cleaner HD channels that help KUSU build a larger audience by offering diverse streams of content.  It also lowered project costs and will help keep operational costs lower for years to come.

-- By Alex M. Perchevitch, President of Jampro Antennas, Inc. Alex@Jampro.com www.jampro.com 916-383-1177

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