Going to Digital ENG: 30 Months and Counting

All 2-GHz broadcast equipment will be upgraded to digital technology and will be operating under a new band plan that keeps the same number of channels but reduces their width to 12 MHz.
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In 30 months, all 2-GHz broadcast equipment will be upgraded to digital technology and will be operating under a new band plan that keeps the same number of channels but reduces their width to 12 MHz. Furthermore, this change will be paid for by Nextel as part of its agreement with the FCC to give up 700 MHz and 800 MHz spectrum in exchange for 10 MHz of new spectrum at 1.9 GHz, 5 MHz from what used to be broadcast auxiliary service Channel 1. I've covered the FCC side in my RF Report e-mail newsletter, and Nextel has discussed it in broadcaster meetings.

Implementing the plan will require the cooperation of broadcasters, Nextel, equipment vendors and installation crews. Nextel plans to commence relocation in groups of seven markets every two-and-a-half to three weeks. This will require careful scheduling of manufacturer production schedules, tower crews and equipment installers.

Now that Nextel has accepted the FCC plan, broadcasters need to do their part to make sure they don't hold up the conversion. The first step is to form a local committee to handle the local transition. Each SBE chapter will have a Nextel-employed regional broadcast engineer assigned to help it. At your station level, identify who will represent the station in negotiation with Nextel.


While this is likely to be the technical operations manager or chief engineer, people from the news, accounting and legal departments and the station manager are likely to be involved. Nextel plans to discuss umbrella agreements with group owners to handle common issues at the corporate level while keeping nuts-and-bolts issues at the local level.

(click thumbnail)Nextel has agreed to cover the cost of converting ENG microwave radio equipment, ancillary equipment (such as MPEG encoders/decoders, LNAs and filters), talent-cueing equipment, control systems, multiband antennas and even backup equipment. The labor and administrative costs of changing out the equipment are also covered. Don't expect Nextel to cover the cost of omnidirectional antennas (which aren't a good idea anyway if spectrum efficiency is a concern), or upgrading receive sites to new quad-polarized antennas.

In early April, Nextel will have an inventory form online for stations to fill out to get reimbursed for digital equipment purchases. If you want to start earlier, Nextel can provide an Excel spreadsheet. Broadcasters can choose their own equipment, but Nextel has worked with microwave equipment manufacturers to come up with basic packages for the conversion. If your equipment selections include features beyond those included in the packages, expect to pay the difference in cost.

I recommend taking a systematic approach to determine what you will need to replace or upgrade. Look at the ENG trucks. If you bought equipment recently, it may only need a digital modulator and MPEG encoder to make the switch. Don't forget to include an analog to serial digital converter if your truck is analog and the encoder only accepts SDI. Most antennas should work for digital operation. The exception would be ones with poor return-loss, which likely had problems with analog as well.

The same can't be said for mast-mounted amplifiers. COFDM, with its high-peak-to-average ratio, requires a lower-distortion, more linear amplifier. With analog FM, a Class C amplifier was good enough. With some amplifiers, simply reducing the input power to them will allow them to function as linear amplifiers. This power reduction may be acceptable. If not, the amplifier will have to be replaced.


You may have noticed that talent-cueing was included in the costs eligible for reimbursement. If you haven't used a digital ENG system before, this may seem odd. Efficient video compression requires storing some video in a buffer, which adds delay to the video and, ideally, adds the same delay to the audio. Echoing the talent's voice back to them a second later is a very good way to make them stop talking. If your current cueing system does not have mix-minus, it will have to be modified and Nextel will cover the cost. Nextel won't, however, replace your audio console, although they may consider covering the cost of a mix-minus module. An outboard mix-minus system such the new Mod Sciences ProCeiver is okay.

Once the modifications to the trucks and cueing system are planned, examine ENG receive sites. To avoid the cost and degradation of demodulating and remodulating the baseband signal, many stations simply send the entire baseband or even IF signal back on the return link. These techniques probably won't work with a COFDM digital signal unless the microwave equipment is stable enough (phase and frequency) and includes an adaptive equalizer to remove distortion in the received signal. This means you will not only need to modify the trucks, but the receive sites as well.


Consider whether you want to keep an existing analog return link. In this case, the receive site will need an MPEG-2 decoder to convert the incoming digital signal to analog video and audio. This is probably the easiest approach, since digital ENG receivers include video and audio outputs, and this is the only option Nextel is willing to pay for.

In the future, you may want to vary the bit-rates to allow more than one truck or signal to share a channel. Maybe you want to do HDTV for some shots but not others. In these cases, it makes sense to send the entire digital stream back to the studio and deal with the decoding there, even if you have to pick up the cost of upgrading the return link to digital. The one exception is if the return link is at 2 GHz, Nextel will cover digital conversion on the same band, but not the extra cost of moving it to another band.

There is an item to consider that Nextel will cover. If you use a band-pass filter at the dish, it will have to be changed to match the new band-plan frequencies.

Studio modifications are likely to be minimal. Control systems are covered under Nextel's plan. Spend some time looking at what equipment manufacturers can offer. Some stations feel it is important to have the ability to switch back to narrow-band analog for difficult shots or to peak the antenna, although the COFDM users I've talked to say the technology works where analog won't.

The digital conversion and frequency clearing has to be completed in the next 30 months! Take time now to think through your station's ENG conversion. If you already have DENG trucks on the road, consider how operations could be improved with an all-digital system. Now's the time to make the change!

Your comments and questions on any RF topic are always welcome. Drop me an e-mail at dlung@transmitter.com. Your question may become the basis for my next RF Technology column!