STEVE BURGESS /
09.01.2011
Originally featured on BroadcastEngineering.com
DSNG vehicles
Building a successful DSNG vehicle is not a trivial task. Here's what you need to know.

The challenges of building digital satellite newsgathering (DSNG) vehicles have generally remained the same over the years — those of trying to fit the maximum amount of equipment in a confined space, keep it cool, ensure that it is safe and road legal, and provide a reliable source of power.

Furthermore, the challenge exists of getting the maximum amount of data back from the field in the narrowest pipe. Increasingly sophisticated coding and modulation schemes are being employed to enable either high data rate applications, such as 3-D, or larger numbers of channels for multiple news feeds.

This article focuses on the structural build of these vehicles as opposed to specific broadcast or uplink equipment installed since the brand choice is so varied and is often driven by the broadcaster's individual preference. That said, there is some level of commonality as many broadcasters continue to commission HD-ready vehicles with an HD-infrastructure or SD components that can be easily upgraded at a later stage. Most video systems are based on HD-SDI, and few decisions today can be made concerning audio without the consideration of how to pass Dolby 5.1 surround sound.

Choice of vehicle

The environment in which the vehicle will be used will influence the choice of chassis. The equipment complement, along with its powering and cooling systems, should also be a major factor. But, many potential DSNG vehicle customers are brought back to reality when the first realistic layouts and weight calculations are done.

The smallest DSNG vehicles tend to be built on sports utility vehicles, people carriers or pickups. These truly can be “fast response, go anywhere” vehicles, and are easy to park and maneuver at any event. On the other hand, the disadvantages of such vehicles include a lack of operational and equipment space and a minimal load carrying capacity. Considering those factors, it is unlikely that these could be used for high-profile production events (where redundancy would be needed), and instead mainly would be for news.

If a larger vehicle is selected, in Europe the next break point is usually the driving restrictions applicable to vehicles over 3500kg. If the gross vehicle weight can be kept below 3500kg, finding drivers with the appropriate licenses is easier, and the operating costs are less. Some of the smaller panel vans fall into this category, and compromises then must be made with options such as four-wheel drive or whether the operators need to stand up in the vehicles. It is important not to fall into the trap of choosing the largest, sub-3500kg chassis available. Invariably, this would result in such a restricted payload that the operators would just fill the space available and cause the vehicle to be overweight the first time it goes out to a job.

The next largest vehicles tend to be around 5000kg gross weight. These vehicles offer the opportunity to carry more sophisticated powering and cooling systems, can have redundancy in the uplink chain and can be four-wheel drive if needed. There is also the possibility to house a reasonably comprehensive (if somewhat compact) production capability. This chassis tends to be the most popular choice.

If more complex productions need to be undertaken, with separate camera engineer, sound and vision operators, the natural selection is a 7500kg vehicle. At this level, it is possible to have a “box body” or a panel van. Obviously, the box body offers much more flexibility in terms of interior space, but cost and delivery times can be longer than the panel van.

The most sophisticated uplink vehicles are often used as communications hubs. These would have large main antennas (around 2.4m) along with other receive dishes and multiple masts. Vehicles for this purpose are usually built on 18000kg to 26000kg box bodies.

Whatever the choice of vehicle, care should be taken to select a reputable coachbuilder. New legislation has been introduced requiring that all new vehicles being modified for use in the EU (adding a dish, roof air-con or even external grills) have to be tested and approved at an official testing station.

In the case of broadcast vehicles, this will be enforced in 2012. However, this is likely to result in increased costs and delays, due particularly to the limited number of testing stations and the variety of vehicles, from various industry sectors, that will be submitted for testing by coachbuilders.

Power

All DSNG vehicles will need varying amounts of AC and DC power supplies to operate both the technical equipment and the utilities (lighting, heating and cooling). Ideally, both of these need to be derived from systems built into the vehicle.

The natural choice for the 230V AC power is for the vehicle to carry an on-board, self-contained generator. The disadvantages of these are mainly weight and noise. Typical 12kVA water-cooled, diesel generators will weigh up to 300kg. Soundproof capsules can minimize noise, but these also add to the overall weight. Opting for a petrol generator can reduce generator weight and noise, but almost invariably the vehicle engine is diesel, adding the requirement for an extra fuel tank. Air-cooled generators can be lighter than water-cooled versions, but these also tend to be noisier. Despite all these challenges, the on-board, water-cooled, diesel generator is still the most popular choice. Towable or removable generators are also options, but neither is particularly convenient.

It is possible to fit an extra 230V alternator to the vehicle engine. Space can usually be found in the engine bay for something capable of up to around 5kVA. If more power is needed, then some kind of power take-off is needed elsewhere (such as under the vehicle). This solution is noisier than the separate generator and not particularly economical given that it requires running a two-liter to three-liter engine in a mode it was not designed for. An engine-driven generator is often a good solution as an emergency backup.

The quietest solution is the inverter/charger system. This is often used when the main source of AC is power from a local supply line or site generator, which keeps a bank of batteries charged. In the case that separate power is not available, the batteries supply power to the equipment through an inverter. Although this is not a true online UPS system, the break that occurs on switchover between charging and inverting can be made fast enough to avoid disturbing most of the technical equipment. This system has the advantage that the battery charging can be linked into the vehicle's alternator, so the run time is extended by starting the engine. Unfortunately, however, batteries are quite heavy, so capacity is always a compromise.

All of the above systems can be combined with an online UPS to power some or all of the technical equipment in the case that all power is lost. The challenge is choosing a UPS that is suitable for mounting in a vehicle environment with the inherent problems of heat and vibration. Most UPS's are built for the relative comfort of an office or data center environment.

Another strain on the weight budget comes with the addition of an isolation transformer, with typical 7.5kVA transformers weighing around 70kg. In many countries, this is a legal requirement. The transformer also helps to create a safe environment inside the vehicle, but it is important to choose a design that is able to handle the high harmonics often encountered from supplying many items of equipment.

As with the coach building, legislation plays its part in the vehicle's electrical system. This must be tested by a competent person and a certificate issued. This can be done by the installer, provided test engineers are available with the appropriate training and appropriate test equipment.

Some of the technical equipment and much of the lighting will run from either 12V or 24V DC. Experience and feedback from operators have taught us that it is better to use the vehicle battery for this purpose rather than fitting a separate technical battery and charging system. A good quality, intelligent charger must be installed with adequate metering to ensure that the vehicle battery is always kept in good condition. An automatic device is often fitted to disconnect the technical load should the battery capacity fall to a level that may result in it being unable to start the vehicle. Lighting circuits will usually be on a timer circuit. A separate, smaller starting battery is usually fitted for the generator, and a “start assist” connection can be provided to ensure that one can always be started from the other if needed.

Also, the proliferation of LED lighting has cut the DC load significantly in recent years.

Heating and cooling

Given the restrictions of weight, space and power, heating and cooling DSNG vehicles is always a major challenge. The first task is to perform heating and cooling calculations to establish the capacity needed to maintain a comfortable working environment based on given external temperatures, thermal conductivity and heat generated inside the vehicle (along with a few air changes per hour to keep the operators alive). The biggest variable is the thermal conductivity of the vehicle and theoretical calculations are really not satisfactory. The only way to know this for sure is to use experimental data from a number of coach-built vehicles, and in this respect, a paint shop is extremely useful as a laboratory. Techniques have been developed to improve the thermal properties of panel vans and reduce the average U-values considerably. Fitting blinds or curtains to the cab, or fitting and retaining a cab bulkhead can help.

The ideal cooling solution is the split system with inverter technology built into the compressor, as typically fitted to larger production OB vehicles. Their size and weight make fitting these on 5000kg vehicles or smaller extremely difficult. The most frequently implemented cooling systems are those designed for recreational vehicles (RV). These can be roof-mounted or interior, single-piece units or split systems, and provide a capacity up to around 4kW per unit. Apart from overall capacity, a suitable refrigerant must be chosen — one that is legal and easily available in the country of destination and can cope with the ambient temperatures expected.

In the case of the simple on/off type compressors, it is useful to fit a soft start device. Not only will this prevent disturbances on the power supply as the compressor cuts in and out, but also it will prolong the life of the excitation capacitors if the air conditioning is being fed from an asynchronous generator.

The heating produced from the optional heater elements often fitted to RV air conditioners is never particularly effective. If the DSNG vehicle is destined for cold climates, then a diesel-fuelled heating system should be installed. These are relatively small, lightweight and low power-drain devices that use fuel from the vehicle's tank and burn it on the other side of a heat exchanger to provide warm air that is then blown into the vehicle. Heated floor mats can be used to supplement the diesel heaters, but these do take a significant amount of the precious power supply.

While on the subject of heating, the exterior must not be forgotten. The oil used in the hydraulics and grease used in the antenna mechanisms must be chosen according to the climate. Furthermore, snow and ice can be a real problem to these moving parts. Just as with earth station antennas, methods are needed to keep the vehicle antennas free to move in the worst conditions.

Conclusion

Building a successful DSNG is not a trivial task and there are many more challenges that could be discussed. There are no specific training courses or textbooks to help; it is just culmination of experience and in-depth knowledge of all the design details. There are many risks and pitfalls, and the overriding recommendation to anyone looking to build a DSNG vehicle is to be to choose a partner with plenty of experience.

Steve Burgess is technical director at Megahertz Broadcast Systems.



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