GPB Picks Hitachi-Comark for VHF Repack

Two Parallax transmitters were installed at WGTV, each including a separate cooling system. (Image credit: Georgia Public Broadcasting)

ATLANTA—Georgia Public Broadcasting (GPB) operates a state-wide PBS TV network using nine full-power DTV stations and a handful of low-power translators. All but two of our high-power stations were already using high- band VHF channels prior to the FCC repack, so it was reasonable to assume most of these stations were safe from having to move from the pre-repack channels to new ones. 

As luck would have it, five of the state’s seven VHF stations were repacked and therefore required new transmitters. Two of our stations that operated on UHF channels opted to sell their spectrum and switch to VHF low-band (WJSP and WNGH).


GPB only had one DTV station in the early phase of the repack (WJSP). We thought air-cooled transmitters would be the best way to move forward so we ordered a 12kW air-cooled unit from Hitachi-Comark for this station on VHF Channel 5. We also looked at the remainder of our station’s requirements for repack, most of which were in the later phases of the process. Upon further discussions with Hitachi-Comark, we chose the company’s Parallax liquid-cooled DTV transmitters to satisfy our remaining requirements.

Hitachi-Comark’s Parallax series offers several advantages, including high efficiency, minimal requirements for in-building air conditioning and low acoustic noise levels inside the transmitter facilities. We ordered the balance of our repack DTV transmitters from Hitachi-Comark and swapped out the original air-cooled transmitter at WJSP for a Parallax liquid-cooled replacement.  All of the Parallax transmitters deployed use a single cabinet design, varying from 4.3kW “V3” (three PA’s) through 15.9kW “V11” (eleven PA’s). Each transmitter is paired with a separate indoor cooling module with dual pumps and an outdoor dual-fan liquid-to-air heat exchanger.


Field deployments went very smoothly. Hitachi-Comark assigned a program manager who oversaw our entire project from start to finish. First, they performed comprehensive site surveys at all our transmitter facilities to ensure all details were documented prior to actual on-site work. New transmitter equipment and associated accessories were deployed systematically to each repack transmitter site directly from the vendor’s facility. Hitachi-Comark’s installation crews were highly professional and extremely efficient with their on-site work.  

One of our most difficult site locations was WGTV, with a transmitter facility located on top of Stone Mountain Park. The mountain has an elevation of just under 1,700 feet AMSL—great for broadcasting, but difficult and highly dependent on weather conditions to access. Additionally, we could not modify the building to accommodate new equipment.

We installed two new Parallax transmitters (main and standby) in the basement of the building at WGTV. Each transmitter included a separate cooling system for complete redundancy. Speaking of cooling systems, the outdoor heat exchangers needed to be mounted to the roof of the building—three stories above the transmitters. Hitachi-Comark even designed and supplied a custom mounting frame for both heat exchangers, utilizing existing mounting points from the previous analog systems. It was also extremely difficult to route the interconnected cooling system hoses between the outdoor heat exchangers and the indoor equipment.

Even with all these constraints, the team at Hitachi-Comark did a great job. They delivered the equipment on time and on budget. We are glad we chose to work with Hitachi-Comark, and would recommend them to anyone looking for new equipment and field services.

Adam Woodlief has served as the chief technology officer for GPB since 2018. He currently serves on PBS’s Engineering Technology Advisory Committee (ETAC) and is co-chair of the ETAC Public Safety working group. He can be contacted at

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