HAWAII—The looming repack and stations' aging transmitter plants had broadcast engineers taking a fresh look at transmitters and other RF gear at NAB 2016. Fortunately, they had a lot to see!
Comark was back in the Central Hall location it shared with Thales in the early days of ATSC 1. I remember Comark displaying UHF IOT transmitter cabinets there. This year, Hitachi-Comark's new solid-state Doherty transmitter, which is capable of generating the same power as one of those turn-of-the-century tube monsters, was easy to miss in its prime spot in the Hitachi exhibit as it occupied only one 30-inch cabinet. A 100 kW transmitter would take only four racks!
The Hitachi-Comark PARALLAX uses the latest NXP/Ampleon transistors in a Doherty configuration. Comark claims efficiency around 45 percent across UHF channels 14–36. The amplifier can be configured to operate on higher channels for export or for those unlucky stations ending up in the wireless band. The bandwidth choice is a good compromise between making the amplifier completely broadband and maximizing efficiency. The amplifiers are water-cooled, with the coolant isolated from the aluminum heat sinks so that standard copper plumbing can be used without worrying about copper ions degrading the aluminum.
Photo 1: Inside the Hitachi-Comark PARALLAX
One nice feature of the transmitter is that the amplifier combining system is flexible enough to allow adding amplifiers if additional power is needed in the future. While the combiners would have to be changed, it looks like it could be done if the plumbing and wiring was in place. You can see the combiners in view of the rear of the transmitter in Photo 1. The amplifiers are powered by the same air-cooled, high-efficiency plug in GE power supplies that GatesAir selected for its solid state transmitters.
The PARALLAX shown included EXACT exciters designed by TeamCast exciters that are ATSC 3.0 ready. Jack McAnulty told me that Comark plans to have a complete transmitter up and running at the factory in October so that attendees of the IEEE Broadcast Technology Symposium in Hartford, Conn. can visit the factory and see for themselves how the transmitter performs.
Comark's new transmitter will be competing against established high-power solid-state transmitters from GatesAir and Rohde & Schwarz. Both companies were showing their transmitters at NAB and describing their ATSC 3.0 capability while touting recent sales and installations.
Rohde & Schwarz has upgraded the amplifiers in its THU9 series transmitters. While equipped with the same NXP/Ampleon transistors as the older amplifiers, Rohde & Schwarz has improved the design of the amplifier and cooling to allow the amplifiers to be used at higher ATSC (single carrier) power. A six-rack THU9 transmitter can now provide up to 108 kW ATSC power (pre-filter).
GatesAir introduced two higher power air-cooled transmitters—the UAXT-12 (10.8 kW) and UAXT-16 (14.4 kW). If sufficient air is available, these transmitters will greatly simplify installation by not requiring plumbing to outdoor heat exchangers. Combining one of these transmitters with a tunable mask filter could make for a very flexible and almost “plug and play” transmitter installation.
FILTERS & RF COMPONENTS
All TV transmitters require “mask” filters that are tuned to the channel being transmitted and reduce emissions outside the channel to FCC limits. Much of the interest in antennas and RF filters is driven by the repack, but smart buyers will be also be making sure the filters will work after they switch to ATSC 3.0. ATSC 3.0's OFDM modulation can occupy more of the channel and has a higher peak-to-average power.
For the repack, stations may decide to install an “interim” transmitter on their existing channel to use while the main transmitter (and antenna) is being switched to the new channel. In such cases, having a tunable mask filter will allow the interim transmitter to be used as a backup on the new channel after the repack is complete. Stations may also have the option of selecting a different channel than the one they were assigned in the repack, if they can meet FCC coverage and interference requirements. A tunable mask filter is useful if a future channel change is anticipated.
I didn't expect to see any radical new filter designs at NAB and wasn't surprised, although I didn't have time to visit every exhibit. The major improvements promoted were less insertion loss, easier tuning, and increased power handling capability.
ERI introduced a higher-power model of its UF tunable UHF mask filter. It is now available for operation up to 20 kW (liquid cooled). For VHF, ERI's new VF-H8600 combiner allows two high-band VHF stations to share a single antenna provided they are at least four channels apart.
Dielectric offered air tunable UHF filters capable of handling up to 50 kW air cooled or 30 kW convection cooled.
RFS tunable UHF filters are compact and can be water cooled for operation up to 50 kW. RFS was touting its shipment of a filter/combiner system for KXAS/KXTX in Dallas and its order for the antenna/combiner system to be installed at One World Trade in New York City.
Spinner was showing a product of interest to owners of high-power broadband panel antenna systems. These systems are shared by multiple broadcasters, so detecting anomalies in the line and antennas before catastrophic failures occur is critical. Spinner showed a product that looked like a directional coupler assembly but they claimed is able to detect arcing and connector problems after the power dividers on broadband systems.
Unfortunately, I wasn't able to find any information on it on their web site and Spinner was not willing to reveal how it worked. Another engineer I talked to thought it may work by “listening” for arcs or other disturbances in the line. The system Spinner was showing at NAB was designed for use with 4-inch or smaller transmission line, but I don't see why it couldn't be modified for use with larger line. Based on my conversations with engineers planning high power broadband antenna installations, there is certainly interest in it!
Tower structural limits, limited availability of tower crews and equipment, possible zoning/permitting issues and limited resources for designing and manufacturing antennas may reduce broadcasters' options during the short period allowed for transitioning to the new channel. Replacing a top mount stacked slot antenna on a 2000-foot candelabra shared with other stations may be impossible in the time allowed. In such cases, alternatives include using lighter weight, easier to install, side mount antennas or moving to shared broadband antennas.
The good news is that antenna manufacturers are gearing up for the repack by adding staff and boosting manufacturing capacity and providing tools to help broadcasters and their engineers determine what antennas they will need.
ERI announced a deal with T-Mobile that it said will enable it to increase production capacity by 800 percent. ERI had a new broadband VHF panel antenna with a variety of mounting options and a choice of horizontal or circular polarization that should help stations moving to high-VHF. See http://www.eriinc.com/Resources.aspx for information useful in repack planning. I had no problem downloading and installing the ERI Broadcast System Planner V 7.20 on Linux using WINE, although it looks like the software needs to be updated to include the newer antennas.��
Dielectric showed a new lightweight UHF broadband side mount antenna, the TFU-WB, which has 75 percent less wind-load than panels. Azimuth pattern options are limited to two cardioid patterns. Elliptical polarization is available. The antenna's input power rating of up to 60 kW with 24 bays and an azimuth gain of 1.5 or 2.3 (depending on pattern) enable effective radiated power up to the 1,000 kW FCC limit, important if the antenna is mounted lower on the tower.
Dielectric introduced several planning tools, including “Your Guide to the FCC TV Channel Repack”. Dielectric's software for designing antennas is available at http://www.dielectric.com/software/. Once registered, Dielectric's DASP can be downloaded for off-line use or used online. I had no problem using the online version on my Android 5.1 tablet!
RFS presented “Future-proof Antenna Systems” at NAB, outlining some scenarios for the repack, the RF options RFS provides, and some nice photos of the antennas for One World Trade Center and the KXAS/KXTX installation in Dallas.
In this article I've mentioned only some of the more popular companies showing RF products at NAB 2016 that I had a chance to visit and only a few of their products. There are other options for transmitters, filters, and antennas that might better suit your specific needs that you shouldn't ignore.
In my next article I'll cover the ATSC 3.0 innovations at NAB 2016 and the ATSC 2016 Broadcast Television Conference. There's been an amazing amount of progress!
I welcome your comments and questions. Email me at firstname.lastname@example.org.
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