Surviving the 2GHz transition - TvTechnology

Surviving the 2GHz transition

The biggest impact of the relocation will be on ENG equipment and operations. However, fixed links also must be moved in a seamless manner
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Figure 1. Existing and new 2GHz BAS channel plans. Click here to see an enlarged diagram.

Nextel moved ahead with the 2GHz BAS relocation plan beginning on February 7. According to the Report and Order, negotiations with Nextel's stage one markets must be completed by May 31. Because of time-line changes made by the FCC, the stage one deadline was moved to July 15, with projects expected to be under way by mid-year. The stage two mandatory negotiation deadline is now May 15, 2006.

Most broadcasters are acquainted with the new rules as stated in FCC document 04-168, requiring 2GHz BAS operations be moved to 12MHz channels in the new 2025-2110MHz band. (See Figure 1.) Questions remain, however, about the tactical issues of making the biggest and most complete frequency and band change in history, and completing it in a 30-month time frame.

Arguably, the biggest impact of the relocation will be on ENG equipment and operations. However, fixed links also must be moved in a seamless manner. The key to a wholesale replacement of ENG facilities is in broadcasters continuing to provide day-to-day news coverage, while undergoing a forklift upgrade to their 2GHz microwave systems.

Review and inventory your system — again!

No one can predict with absolute certainty where trouble spots will develop. However, there are a few common areas to be aware of.

This refers to Nextel's obligation to provide “comparable” facilities. New ENG central receivers and portable transmitters are obvious targets for replacement, but related hardware and subsystems should be completely reviewed with regard to their impact on maintaining ENG station operations.

The question of dual mode versus an all-digital system is another area that deserves examination. While an all-digital system may seem less complicated, it may not be comparable to what you now have in several ways.

One possible problem in a digital world is that all radios may not be compatible in digital mode, while analog FM is universal. When traveling outside of your normal area, analog may be a common thread. Also, analog can be used as a backup mode if an issue develops in the ENG digital decoder. Finally, 2.5GHz is not under the relocation order and can still be used as full bandwidth 17MHz analog channels in areas where interference is not an issue.

The comparable facility requirement applies equally to antenna systems as well. In a world with digital and analog systems operating side by side, the potential for adjacent channel interference will be difficult to predict as it will be random in nature. It is generally understood that COFDM signals work well in a multipath environment and that linear polarization is sufficient in many cases, but that's only half the story. Having the added discrimination of RHCP, LHCP, and horizontal and vertical linear polarization could mean the difference between getting the story and not getting it. If you have a linear antenna system, a quad polarized system may be the answer to comparable facilities in a post relocation environment.

Another potential problem area is the LNA. Most LNAs now in service cannot handle strong digital signals without going into compression. With analog transmission, the effect of overload can be quickly recognized by streaking in the video; in digital, the monitor just goes black, which can easily fool an operator into thinking the signal has been lost, when in reality, it's too strong. It's hard to imagine that reducing the RF level will bring the video back, but that's what is needed in a case like this. The cure is a replacement LNA with AGC. Existing RF channel filters will be on the replacement list as well.

Train your operators well in advance

Don't forget the flexible cable coils on the antenna mast in your ENG van. They may not have enough conductors to support new mast-mounted electronics. Take a second look at your requirements.

Operating a digital ENG link is not at all similar to operating an analog link. The encoder/decoder delay can easily trip you up when panning the antennas for best signal. You may find it easier to set up on analog and then switch to digital.

Get involved in the process

Many news directors are understandably apprehensive about the digital cliff effect and the difficulty in predicting when it will render a shot useless. Although digital quality monitors are now becoming available, until they are mainstream, there are alternatives. Low-cost, remotely accessible spectrum analyzers can provide a real-time view of the COFDM pedestal at the central receive site via a LAN or Web base interface. With a bit of experience, watching the analyzer display on a PC gives an operator the ability to see trends as they happen and to develop a feel for where the infamous cliff might be hiding.

The actual procedures that will be used during equipment replacements are still being discussed by Nextel, manufacturers and industry groups. The most likely scenario will be to replace the central receivers first, followed by the mobile gear. Initially, as the gear is replaced, everyone in a target DMA will continue to operate on the old channel centers until all of the equipment replacements in the DMA are completed, tested and ready. At a mutually agreeable time, everyone will switch to the new plan.

Some of the installation issues that are still being debated include how and when to change existing antenna components such as LNAs and channel filters. If your system requires one or more filters in the antenna housing, multiple filter sets that can be switched between the old and new channels may be required on a temporary basis. Be sure to check your control cable to see if it has enough extra conductors to support filter switching and AGC. You may need to be replace it.

Your best defense in this relocation period is good offense. Develop a transition plan that works for your operation, and talk to your Nextel coordinator about it. If you need an independent opinion, the Society of Broadcast Engineers (SBE) has a full-time coordinator working with Nextel on behalf of the broadcast community. Information is available on the SBE Web site at www.sbe.org.

George Maier is the founder of Orion Broadcast Solutions.