NCP-8
Retrofit Noise Control Package for
Mode-S Radar Sites

NCP-8
DESCRIPTION OF DESIGN

The NCP-8 is a noise control device engineered for use with the Mode-S. It is designed to be an integral part of the Mode-S system in both function and appearance. NCP-8 is composed of 4 inlet and exhaust noise baffles.

INLET

The inlet baffle of the Mode-S is a roll around absorptive barrier. It has handles and ball wheels for easy positioning and removal. This baffle incorporates the acoustic plenum method for noise control. The 100% free air flow entry into the baffle occurs at the floor line as well as at the top opening. The sides of the baffle are sealed to the face of either type of Mode-S doors.

EXHAUST

The exhaust baffle for the Mode-S is a small cabinet top that incorporates the absorptive acoustic barrier method for noise control. The leg supports leave all sides open, allowing absolutely unrestricted air flow. It is lightweight, easily handled and can be used with either style of Mode-S exhaust openings.

SOUND BAFFLE FOR THE MODE-S
SPECIFICATIONS AND SAFETY DATA

ASC was commissioned by the FAA to develop a noise suppression system for the ASR-9 and the Mode-S. Great care was taken to accommodate the stringent demands from the FAA for safety, durability, design and ease of installation. ASC not only met those criteria but surpassed them with the development of the NCP-10 for the ASR-9 and the NCP-8 for the Mode S.

The NCP-8 is 100% welded construction of 18 gauge galvanized and etched sheet metal. The floor standing units are supported by four ball bearing casters, with a load capacity of 75 lbs each, and have handles attached at either end for easy handling.

The NCP-8 is electrostatic powder coat painted. This is a highly scratch resistant surface that is color matched to the Westinghouse built Mode-S, as is our NCP-10 to the ASR-9. The weights are: 64 pounds for the roll around air inlet unit and 16 pounds for the exhaust noise baffle.

The sound absorbing material used in the NCP-8 is a 2" fiberglass panel extensively used in the HVAC industry. The fiber shedding of this panel is well below the permissible exposure limit (REL) proposed in 1977 by the National Institute of Occupational, Safety and Health (NIOSH) of 3.0 fibers/cc. All cut edges of the sound absorbing material are coated with a fiber retaining sealant. In addition the surface and edges are covered with a spunbond polypropylene dust cover. The dust cover is then covered with a 40% open weave monofilament plastic screen. This final surface handles wind and any other mechanically abrasive contact.

The NCP-8 is designed to meet the same handling and stacking requirements as the NCP-10 system. They nest efficiently, requiring minimal floor space for storage. All noise baffles are able to be easily and quickly removed from the signal processing cabinets. When rolling, the cabinets are well balanced and stable. The baffle equipment is designed to interface with the Mode-S without risk of damage to other FAA equipment. Another FAA requirement is interchangeability. Our noise baffle is engineered to fit either of the Mode-S doors. The exhaust units are also interchangeable.

The lifetime of the NCP-8 unit is expected to be indefinite when used indoors and for its intended purpose.

NCP-8
ACOUSTIC PERFORMANCE

MODE-S REPORT

The noise level for a commissioned Mode-S has been measured to be 86 dB,A at the face of the air inlet grill. The NCP-8 inlet baffle was tested in the lab and the results compared to the field measurements of the Mode-S inlet noise. The results were as follows: (All measurements are in dB,A)

An air inlet noise baffle was designed and built to fit the Mode-S cabinet and to meet FAA handling requirements. This roll around noise baffle is a plenum baffle. It measures in the laboratory mock up testing to produce 16 dB,A attenuation as measured at the upper inlet opening of the baffle. This is well within the performance expected from this plenum baffle design.

The sound source used in these tests was flat within 3 dB,A when filtered through the weighting filters. This is very close to the actual sound source spectrum. The lab noise source that measured 84 dB,A at the opening was reduced to 68 dB,A at the opening of the baffle. The baffle produces 16 dB,A attenuation. With the lab tests we have demonstrated that our sound baffle meets the needs of the site. Noise levels at the inlet of the Mode-S read 86 dB,A. Our NCP-8 baffle will knock down 16 dB,A and the resulting noise level at the air inlet opening of the baffle will be 70 dB,A. Noise output from the baffle will always measure less than this 70 dB,A regardless of where the measurement is taken.

ACOUSTIC TESTING

With these tests we have demonstrated that our sound baffle design meets the needs of the site. Sound at the opening will be 72 dB,A and will measure substantially less than the 78 dB,A at the 5 foot distance requirement.