RF EXPRESSSTLs: Your Last Link
Much attention has been paid over the last year to transmitters, towers, and antennas. However, one critical RF area seldom mentioned is the studio-to-transmitter link (STL). What’s nudged it to center stage is the fact that the DTV-ready transmitters being installed will need a DTV feed.
Co-located studios and transmitters don’t face this problem, but those with transmitters on the other side of town or up on a mountain are already dealing with it. Those who have yet to install a DTV transmitter will need to put STLs on the front burner.
The problem across the industry is that those STLs that have been on-line for many years aren’t good candidates for retrofitting. “Even if they could be modified,” said Eric McCulley, “they would have to be pulled out of service and sent to the manufacturer’s factory.” Obviously, that’s not the best scenario.
McCulley, manager of Business Development at Microwave Radio Communications (MRC), suggests that TV station engineers contact manufacturers to check out their options. However, he insists that the older the STL, the less likely it is that it can be updated. Even if this possible, he says it may be economically prohibitive.
Some stations have opted to use fiber optic lines to feed the transmitter, but as MRC’s Vice President of Marketing and Sales Dave McIntyre said, “That’s a costly alternative. Besides, fiber optic lines aren’t always available where you need them.
“There’s also the ‘Backhoe Fade’ problem to consider. That’s what we call it when a backhoe on a construction site digs into your fiber optic cables. That’s why we say that in the long run microwave is more reliable.” He added that some stations have opted for using both microwave and fiber, with one as the main feed and the other as an alternate.
Making The Connection
Up on Mount Wilson, near Los Angles, DTV transmitter installations have been brisk. Axcera says it’s been in the process of delivering seven transmitters to the mountain, most recently for KXLA, KJLA, KOCE, and KDOC.
MRC has supplied many of the STLs linking Los Angeles and Mount Wilson. McIntyre, long familiar with the city’s temperature inversions and the smog that comes with them, acknowledges that in some cases, inversions are likely to cause a microwave feed problem. In that case, MRC refers station engineers to its two-antenna diversity system, which solves the problem.
Basically, MRC has been solving the dual-carrier problem since 1998, when it first offered its TwinStream dual-carrier analog/digital microwave system to the market. The system also supports non-protected, hot standby, or receive diversity configurations, and offers several upgrade paths.
MRC’s DAR Plus analog or digital microwave system can carry conventional video and audio or digital transport with rates of up to 120Mbps. It can be made field switchable from analog to digital by changing a few switch settings in the RF shelf. It can also be reconfigured using the DAR Plus Menu System. This provides full control of the radio with alarm reporting and status.
The Choice Is Yours
For those stations still plowing through the DTV transition, I suggest pulling out your DigitalTV-Television Broadcast 2002 RF Express Directory and contacting your preferred STL suppliers.
As MRC’s offerings suggest, there are many STL options available today, and that’s important, because no two stations are confronted with exactly the same terrain and/or economic obstacles. NAB attendees will likely discover many viable STL solutions. But, as McCulley insists, make certain your manufacturer of choice understands your old STL system and your current and future concerns.
> Microwave Radio Communications
Ron Merrell is the executive editor.
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