Wurth, Timothy J.; Rodzinak, Jason; NuWaves Engineering (International Foundation for Telemetering, 2007-10)
      Meeting the filtering requirements for telemetry transmitters and receivers can be challenging. Telemetry systems use filters to eliminate unwanted spurious or mixing products. The use of tunable microwave filters for both L and S Band can improve filter selectivity and provide low insertion losses in the filter passband. Along with meeting specifications, these microwave filters with the ability to tune an octave, reduce size and cost by the reduction of multiple, fixed-frequency filters. As size, weight and power are often a concern with aeronautical telemetry systems, this paper will demonstrate that microstrip tunable filters can be small in size and use minimal power. Telemetry transmitters are subject to difficult spurious emission and interference specifications and require selective filters to eliminate spurious signals before the final amplification. Telemetry receivers on the other hand are subject to intense Image and Local Oscillator (LO) rejection requirements and demand low insertion loss for front-end filtering. Low insertion loss filtering before the Low Noise Amplifier (LNA) circuit limits degradation to the system noise figure (NF). By using different filter topologies and state-of-the-art, high-Q varactor diodes, tunable microwave filters can be optimized for two different functions. The two functions emphasize either low insertion loss or selectivity. An important design consideration with tunable filters, when compared to typical fixed frequency filters, is the degraded intermodulation performance. This is largely due to the non-linear behavior of the varactor diodes. This paper describes the benefits and limitations of microwave tunable filter architectures suitable for both aeronautical telemetry transmitters and telemetry receivers. Information on the computer modeling of varactor diodes will be covered as a critical part of the design. Potential design considerations for microwave tunable filters will also be covered. Through the use of simulation software and filter prototypes, this paper presents dramatically improved filter performance applicable to telemetry transmitters and receivers.

      Trimble, Michael L.; Wells, John E.; Wurth, Timothy J.; NuWaves Engineering (International Foundation for Telemetering, 2007-10)
      Tactical training ranges provide an opportunity for all of the armed forces to assess operational readiness. To perform this task the various training ranges have deployed numerous telemetry systems. The current design efforts in place to upgrade the capabilities and unify the ranges under one telemetry system do not address the training ranges' need to maintain their training capability with the legacy systems that have been deployed until the new systems are ready. Two systems that have recently undergone sustainment efforts are the Player and Event Tracking System (TAPETS) and the Large Area Tracking Range (LATR). TAPETS is a telemetry system operated by the U.S. Army Operational Test Command. The TAPETS system is comprised of the ground mobile station Standard Range Unit (SRU) and the aircraft Inertial Global Positioning System (GPS) Integration (IGI) Pod. Both systems require a transponder for the wireless communications link. LATR is an over the horizon telemetry system operated by the U.S. Navy at various test ranges to track ground based, ship based, and airborne participants in training exercises. The LATR system is comprised of Rotary Wing (RW), Fixed Wing (FW) Pods, Fixed Wing Internal (FWI), Ship, and Ground Participant Instrumentation Packages (PIPs) as well as Ground Interrogation Station (GIS) and relay stations. Like the TAPETS system, each of these packages and stations also require a transponder for the wireless communications link. Both telemetry systems have developed additional capabilities in order to better support and train the Armed Forces, which consequently requires more transponders. In addition, some areas were experiencing failures in their transponders that have been deployed for many years. The available spare components of some systems had been depleted and the sustainment requirements along with the increased demand for assets were beginning to impact the ability of the systems to successfully monitor the training ranges during exercises. The path to maintaining operational capability chosen for the TAPETS system was a mixed approach that consisted of identifying a depot level repair facility for their transponders and funding the development of new transponder printed circuit boards (PCB's) where obsolescence prevented a sufficient number of repairable units. In the case of LATR, the decision was made to create new transponders to take advantage of cost effective state-of-the-art RF design and manufacturing processes. The result of this effort is a new transponder that is operationally indistinguishable from the legacy transponder in all installation environments. The purpose of this paper is to present two successful system sustainment efforts with different approaches to serve as models for preserving the current level of training range capabilities until the next generation of telemetry systems are deployed. While the two programs illustrated here deal primarily with the transponder components of the systems, these same methods can be applied to the other aspects of legacy telemetry system sustainment efforts.