The RFIMS program effort was divided into three tasks. Task 1 included an assessment of requirements, option evaluations, and development of a measurement system specification. Task 2 included system acquisition and testing of a prototype RFIMS, delivered in February 1998 to the FAA. In task 3 ITS assembled, tested and delivered the remaining ten systems. In fiscal year 2000, ITS delivered the last two RFIMS vehicles to the FAA. Each system was assembled and tested by ITS personnel to assure peak performance upon delivery.

Figure 1. A production RFIMS vehicle (photograph by B. Bedford).

Figure 2. The spectrum signature measurement panel. (Click on figure to enlarge.)

The RFIMS development process was divided into three major subsystems: the vehicle, the Integrated Electronic Package (IEP) hardware, and the Measurement Control System (MCS) software. The vehicular platform is a Ford Econoline outfitted with three six-foot equipment racks (Figure 1). The IEP is designed to use commercial off-the-shelf measurement equipment, but includes three devices that were designed, developed and assembled by ITS. These devices are a mast-top signal preamplifier and preselector system, an automated measurement path selector and an automatic/manual controller device for the mast-top system. These three devices are not available in the commercial market and represent innovative and unique solutions developed at ITS. The MCS (written in LabView ) controls the measurement system and records and documents the automated measurements. Information automatically recorded in every scan includes data, antenna factors for antennas, measurement system gains and losses, and equipment parameter settings.

The IEP integrates various test and measurement devices to produce a system that is capable of more sophisticated measurements than would be possible with the individual devices. The IEP is subdivided into three areas. The first area is the antenna package. Four antennas are provided to encompass the range of frequencies and measurement scenarios that are envisioned by the FAA. An antenna mounting assembly, designed and constructed by ITS, is provided to aim the antennas (when necessary) and adjust their polarization.

The second area of the IEP is the mast-top signal preamplifier and preselector system. This system provides filtering to reject unwanted signals. It also provides amplification to create a highly sensitive measurement system. The third area is the rack mounted equipment, which includes a commercial spectrum analyzer, a communications test set, and an oscilloscope. Signals to be measured are routed to the commercial test and measurement equipment by an ITS-designed automated measurement path selecting device. This device channels the incoming signal to the appropriate measurement device under manual or computer control. Another rack mounted, ITS-designed device provides manual or computer control of the mast-top signal preamplifier and preselector system.

The MCS incorporates a suite of custom measurement routines specified by the FAA. These automated capabilities allow the FAA to perform standardized computer-controlled measurements that would be impractical to perform manually. This includes those measurements that require highly repetitive tasks and extensive post processing. An example of this type of measurement is the Air Traffic Control Radar Beacon System (ATCRBS) antenna pattern assessment. This measurement utilizes a unique algorithm that resulted in a patent for novel use of software and hardware to determine directional and omni-directional antenna patterns without interrupting beacon operations. Other computer-controlled measurements include a spectrum signature (Figure 2), radar pulse repetition frequency and spectragraph. The spectragraph graphically shows the time variation of the spectrum. This unique ITS-developed tool is useful for determining the causes of interference and intermodulation products.

The RFIMS Program is an excellent example of how ITS can assist other Federal agencies with their spectrum measurement needs. ITS engineers have both the hardware and software engineering expertise, and the knowledge of spectrum monitoring and measurement techniques necessary for automated spectrum measurement design and development.