VERA passive sensor VERA - VERA passive radiolocator ( in Czech known as " Věra " ) is an electronic support measures ( ESM ) system that uses measurements of time difference of arrival ( TDOA ) of pulses at three or four sites to accurately detect and track airborne emitters . Mode of operation . The deployed system typically comprises a central site ( containing the signal processing equipment and an ESM receiver ) and two or three side sites containing only an ESM receiver . The side sites relay the signals received to the central site over a point - to - point microwave link . The central site uses the known propagation delay from the side sites to estimate the TDOA of the pulses at each site . The TDOA of a pulse between one side site and the central site locates the target on a hyperboloid . A second side site provides a second TDOA and hence a second hyperboloid . The intersection of these two hyperboloids places the target on a line , providing a 2D measurement of the target ' s location ( no height ) . A third side - site provides a third hyperboloid , which , when intersected with the line provided by the other two side sites , provides a full 3D location of the target . This process is known as multilateration . The height of a target with an SSR Mode C or Mode S transponder can also be provided by decoding the Mode C or Mode S response directly , which is the normal mode of operation for the civilian VERA - AP system . System accuracy . System accuracy is typically better than a microwave surveillance radar , and is a function of the deployment geometry , the inherent timing accuracy of the central site , the bandwidth of the pulse being detected and the signal - to - noise ratio . Wider separations of the side sites from the central site provide better accuracies – but at the expense of a reduced area of common coverage . Typically side sites are deployed 15 – 40 km from the central site , providing a reasonable compromise of coverage and accuracy . The system is generally line - of - sight limited , with a nominal range of 450 km , the normal radio horizon . Detection of targets is within a sector of approximately 120 degrees , although IFF and SSR targets are detected using a dedicated omnidirectional antenna , and hence may be seen over 360 degrees . Up to 200 targets can be automatically tracked simultaneously , with an output rate adjustable from 1 to 5 seconds . Exploited emitters . The current generation sensor can only detect and track pulsed emissions , due to the requirement to measure the time of arrival of pulses . The receivers operate in the frequency range of 1 - 18 GHz and typically exploit secondary surveillance radar ( SSR ) transponders , identify friend or foe ( IFF ) transponders , airborne radars , weather radar s , tactical air navigation ( TACAN ) transponders , distance measurement equipment ( DME ) beacons , digital communications signals and pulsed jamming signals . Versions . VERA is supplied in a number of versions . VERA - AP is the civilian long - range air traffic control ( ATC ) version , which only exploits civilian SSR transponders at 1030 and 1090 MHz . VERA - E is the export version of the military ESM version of the system , also referred to as the VERA - S / M in its national mobile version . In addition , the shorter range VERA - P3D system is marketed for highly accurate monitoring of transponder - equipped ground vehicle movement at airports . The manufacturers also market an ESM triangulation system known as BORAP . Exports . Open literature sources claim VERA - E systems have been exported to Estonia , Pakistan and the United States . Newspaper reports also claimed that in January 2004 the Czech defence sales company , Omnipol , received licence to sell six systems to China . However , US government pressure on the Czech government resulted in the cancellation of this contract . Civil systems have been widely exported throughout Europe . Within the Czech Republic , a mobile VERA - E unit is operated by the 53rd Passive Radiotechnical Reconnaissance System and Electronic Warfare Centre at Planá near České Budějovice . History . VERA is the latest in a long history of Czech ESM TDOA systems . The first system developed by the Czech army in 1963 was known as PRP - 1 Kopáč which could track 6 targets . This was followed by KRTP - 81 Ramona ( NATO reporting name Soft Ball ) in 1979 , which could track 20 targets , and KRTP - 86 Tamara ( NATO reporting name Trash Can ) in 1987 , which could simultaneously track 23 radar targets and 48 IFF targets . These were widely exported to the former Soviet Union and beyond . These predecessors were manufactured by the state company Tesla , which collapsed after the Velvet Revolution ( 1989 ) . Lead engineers from the former Tesla company formed the ERA Company in Pardubice which produces the current generation VERA family of sensors .