Overview of nonlinear location technology..
Thomas JONES
OVERVIEW OF NONLINEAR LOCATION TECHNOLOGY
Currently, there is a serious discussion among information security experts about the optimal characteristics of nonlinear locators. The wide range of these devices available on the market sometimes causes difficulties for consumers in choosing equipment. We hope that this article will help answer some questions.
Non-linear locators (NL) have been used in search operations for many years. Some experts in the field of technical security have a high opinion of this equipment, while others (due to unsuccessful experience of use) are skeptical about them. The purpose of this article is to clarify a number of issues that arise when using or purchasing NL. When the user understands these technical issues, the NL becomes a very useful tool for conducting search operations.
WHY DO YOU NEED A NL
Many people who are unfamiliar with technical espionage think of eavesdropping devices primarily as transmitters. However, in practice, a variety of electronic devices are used to collect information that are not radio transmitters. This is the strength of the non-linear locator, which can detect and locate any electronic device, regardless of whether it is working or not.
FALSE ALARMS OF A NON-LINEAR LOCATOR
The most common problem that occurs when working with a nonlinear locator is false alarms (responses). Common household electronic devices (phones, electronic watches) will trigger the NL, since they contain electronic components. Such responses are usually easily identified. However, there are “difficult” cases when the responses are caused by metal objects that do not contain electronic components. Therefore, a high-quality nonlinear locator must distinguish real semiconductors from false ones. This article will consider technical problems and solutions related to reducing false alarms of a nonlinear locator.
Many professionals who have had bad experiences with NLJs believe that in order to reduce errors in prospecting, the NLJ should be used in conjunction with an X-ray machine or other equipment that can produce an image of the objects being examined. The use of X-ray equipment is often associated with problems: access from both sides of the wall is required, there is a risk of radiation, and it is difficult to transport due to its size and weight. In most cases, if necessary, I would recommend using a baroscope. In order to look inside the structure being examined, you only need to drill a small, easily sealed hole. For an additional fee, a small portable borescope is included with the REI Orion NLJ. One of the very promising technologies that I know of is the Rascan-2 device, developed in Moscow. This is a very small subsurface location device that uses radio waves to produce an image. However, its resolution is only about 2 cm.
FUNDAMENTALS OF NONLINEAR LOCATION THEORY
The antenna of a nonlinear locator irradiates an object to detect the presence of electronic components. When the emitted signal encounters semiconductor compounds (diodes, transistors, etc.) on its way, it returns at harmonic frequency levels due to the nonlinear properties of the compound. However, false responses are a common problem, since the junctions or touching points of two different metals, oxidation also cause harmonic signals due to their nonlinear characteristics. Such connections are called false. Below are graphs of the current and voltage characteristics of real and false semiconductors, Fig. 1.
COMPARING THE SECOND AND THIRD HARMONICS
Due to the differences in the nonlinear characteristics of the real and false semiconductors, the second and third harmonic responses will have different intensities. When the NL irradiates a real semiconductor, the second harmonic response is stronger than the third. The false semiconductor gives a stronger third harmonic response. Figure 2 shows this effect.
A high-quality NL has the ability to compare the magnitude of the signals at the second and third harmonics. This ability greatly helps the user distinguish real semiconductors from false ones.
However, this quality usually significantly affects the cost of the NL, since in this case it has two receivers. For a NL operating on the second and third harmonics, it is also very important that the receiving channels are well isolated and do not affect each other's operation. Tests of a large number of NLs from all over the world have shown that most of them do not have good RF isolation. This means that a real semiconductor can have a strong response at the third harmonic, and a false one at the second. Therefore, even if the NL operates on two harmonics, it is often difficult to distinguish between real and false transitions. If a NL receives the second and third harmonics, it is very important that its receivers are calibrated and do not affect each other. REI engineers, understanding the importance of this characteristic, developed and applied a patented technology of the receiving path in the NL “Orion”. This patented technology eliminates mutual influence of the receiving paths and at the same time provides a constant display of the levels of the second and third harmonics.
ATTENSION EFFECT
Many professionals rely on the attenuation effect” when identifying semiconductor compounds (Fig. 3).
If you are listening to the demodulated audio response from a semiconductor, when you move the NL antenna close to it, the noise will be significantly reduced. When you move the antenna away from it, the noise will increase and reach a normal level. Audio noise is at its lowest just above the semiconductor and at its normal level away from it. When you move the NL antenna close to a false semiconductor, the audio signal may increase and reach a maximum just above it, or in some cases the noise level will decrease as with a real semiconductor. When you move the antenna away from it, the audio noise will reach its own level.
It is very important to understand that the theory of the «fading effect» is based on a very simple process. Generally speaking, if the LL emits an unmodulated signal, then the received harmonic signal will also be unmodulated, which is expressed in the sound effect of «fading».
The audio demodulation necessary for the «fading effect» can be implemented in both pulsed and constant-wavelength LLs (this will be discussed below). There are several Russian-made NLs that have a “20K mode”. This mode uses the “fading effect as a method for identifying connection types. Based on my personal experience, I cannot say that this is a reliable method for distinguishing between real and fake conductors. Some fake semiconductors are easily identified using the “fading effect”, but many of them cause the “fading effect” (i.e. are identified as real. — NEP note). The Orion NL has a “20K mode” for signal analysis using the “fading effect”, but in fact a more reliable way to use this effect is to listen to the audio with frequency modulation of the continuous signal.
OTHER AREAS OF APPLICATION OF AUDIO SIGNAL DEMODULATION IN NONLINEAR LOCATIONS
When working with NL, it is often possible not only to detect electronic devices, but also to determine their type by listening to demodulated audio signals. For example, when detecting a working tape recorder, you can hear the audio signal from the recording head. Moreover, a good NL provides listening to the synchronizing video signal when detecting most cheap video cameras. When using FM demodulation, you can sometimes hear characteristic periodic or other unique sounds caused by phase switching in working electronic devices.Therefore, it is important to practice using the NL to easily recognize the characteristic sounds inherent in certain electronic devices. If a false semiconductor is detected, the user can easily identify it by listening to the audio signal and simultaneously exerting physical pressure on it (usually by hitting the wall with a fist or a rubber mallet). The false semiconductor will respond in the headphones with a crackling sound. When exerting pressure on a real semiconductor, the operator will hear nothing. The non-linear locator must provide high-quality audio demodulation in both AM and FM modes in order to use its capabilities for identifying connections. The Orion non-linear locator implements a constant emission mode with an FM-modulated tone of 1 kHz. Using this method, it is possible to achieve a very large detection range, provided that the operator can skillfully evaluate the FM-demodulated signal of a high-quality receiver. While the display may show an insignificant response, which can be taken for an increase in the background, the audible tone clearly indicates a non-linear connection. Using FM-modulated tone can significantly improve the detection capabilities of the NL, if the receiver has a high-quality audio demodulator and good isolation from the transmitter. However, the modulated tone mode does not provide the ability to distinguish a real semiconductor from a false one.
CONTINUOUS VERSUS PULSED RADIATION
Most nonlinear locators developed in the world are devices emitting a continuous signal in a narrow band. However, there are a small number of NLs that use a pulse mode, which has its advantages. The advantage of the pulse mode is lower current consumption, provided that the transmitter is well designed. For example, the receiver receives signals with a frequency sufficient for human vision and hearing, and turns off the transmitter for sufficiently long intervals. This characteristic reduces the requirements for the size of batteries and current consumption. Moreover, to implement the attenuation effect, the receiver of a continuous-wave nonlinear locator must have a high-quality low-frequency amplifier and demodulator. On the other hand, the method of demodulating audio is radiation in a pulse mode. If the pulse repetition frequency is above the hearing threshold, then a simple amplitude modulation scheme is sufficient for good demodulation quality. It does not matter what radiation a nonlinear locator uses, if it provides good reception of an audio signal and is easy to use. NL Orion” allows listening to the signal in AM and FM modes, using pulsed radiation for amplitude modulation and constant — for frequency modulation. Such a scheme creates the best conditions for the implementation of the “fading effect”.
FREQUENCY INCOMPATIBILITY
Most NLJs operate on a single fixed frequency, some have multiple channels. Due to the increasing number of radio communications devices and government regulations on radio spectrum, NLJs with limited frequency emissions often conflict with other electronic devices. If an NLJ is operating on a busy frequency, its readings may be random and unreliable. This is a common problem in large American cities and, as far as I know, Orion is the only NLJ that solves it. For this reason, the NLJ must operate over a wide enough range and automatically find free channels to operate in.
POWER LEVEL AND SENSITIVITY
Many people evaluate NL by the radiated power, since this characteristic is relatively easy to understand. However, it is very important to understand that the sensitivity of the receiver is as important as the transmitter power. It is also necessary to understand that a NL with low radiated power and a high-quality receiver can have higher detection characteristics than a powerful locator with a poor receiver. It should be borne in mind that a powerful locator can damage electronic devices and even harm human health. I was told that Russian powerful pulse models provide additional signal power in order to activate semiconductor junctions. This is an incorrect premise. A diode is the simplest semiconductor junction and greatly helps to understand the principle of NL operation. Electronic engineers often model a diode as a simple current switch, allowing current to flow in the direction of the positive voltage bias. However, this is an oversimplification that should not be used when analyzing the theory of nonlinear location. A semiconductor junction is a it is not just an “on or off” function, it is a well-defined constant exponential function, shown in Fig. 1 and represented by the formula below:
,
where Io is the leakage current,
q is the electron charge,
K is the Boltzmann coefficient,
T is the temperature,
v is the voltage across the ends of the diode.
Therefore, low-power NLs can have better characteristics than high-power ones if the former have better receivers.
As far as I know. “Orion” is the only NL in the world that uses digital signal processing to improve receiver sensitivity. “Orion provides the ability to significantly increase the detection range by processing the output signal from the receiver. The operator can manually program the amplification level of the processed signal to optimize the NL operating mode. Moreover, “Orion” is the only NL in the world that uses an automatic power control algorithm. If the receiver receives an excessively strong signal, the radiation power is automatically reduced so that the operator can evaluate the response from the semiconductor compound. When the strength of the response signal decreases, the transmitter radiation power returns to the original value. Due to these characteristics (signal amplification level control with digital processing and automatic power control), “Orion” is very easy to use. The operator does not need to constantly adjust the NL during search operations.
ERGONOMIC CHARACTERISTICS
When operating a non-linear locator, it is important to have a good view of the display to evaluate the readings. Some NLs have a display on the transceiver unit, which is carried by a strap around the operator's shoulder or neck. I have found this to be the least effective display solution due to the need to monitor the readings while moving the antenna over different locations. Some NLs have a display on the handle. This is an improvement, but if the display is dull (like an LCD), it is difficult to read the readings while operating the antenna. The best type of display is a very bright display located on the antenna body. This display is easy to read from many angles. A display built into the antenna body allows the user to read the readings while moving the antenna at the same time. If the operator cannot easily read the display, the quality of the search is reduced due to the deterioration of the interpretation of harmonic levels.The non-linear locator has been a very heavy and bulky device from the very beginning. With the exception of the “0rion”, all other NLs that I know of at the moment have a transceiver that must be carried with a strap around the neck or shoulder. The operator holds the antenna in his hand. In all of these NLs, the transceiver is heavy. It has cables to connect to the antenna. Cables often interfere with work, catching on furniture or knocking valuables off tables. After discussing ergonomics with searchers from different countries, I have come to the following conclusion: if the information is difficult to read from the display, and the NL causes rapid fatigue during operation, the detection range or the ability to distinguish between real and false semiconductors does not matter, since the operator will not be able to conduct a quality survey. To ensure effective operation, the NL must be simple and easy to use.
Conclusions
It is important to understand that when a nonlinear locator is operating, two processes occur: (1) Detecting the nonlinear junction and (2) Distinguishing between real and false semiconductors. A nonlinear locator should be judged by both its detection range and its ability to distinguish between these junctions.
In my opinion, the most important characteristic of a NL is its detection range — the depth of penetration of the signal into objects located at the search location. However, the concept of this characteristic must be understood correctly and used only for comparing NL during tests under the same conditions. Moreover, a long detection range does not necessarily characterize a NL well; you may simply detect electronic devices (computers, telephones) in the next room. During operation, the NL must not only have sufficient detection range, but also the ability to adjust it accordingly (usually by adjusting the transmitter power or, as in the case of the Orion, by adjusting the gain of the receiver) to ensure the required detection depth in the material being examined. Historically, NL models in the United States were based only on the comparison of the second and third harmonics. However, it is also important to use audio analysis methods of semiconductor compounds, such as the “fading effect” and physical impact. For maximum reliability, a good NLR should use multiple methods to identify real and false semiconductors.
As noted above, there are many different opinions on the use of non-linear locators. In the United States, some professionals believe that NL should be used for reliable inspection. Others believe that NL should not be used because of too many false alarms or other technical problems. Their opinions differ due to different experiences due to the reasons discussed in this article. REI's Orion NL was designed with the technical and ergonomic considerations discussed in mind. «The Orion provides both continuous wave and pulsed modes that are optimized for maximum detection range, second and third harmonic level comparison, and very effective methods for identifying semiconductor compounds. Its small size allows it to be stored and transported in a package slightly larger than an attaché case. The Orion weighs less than 3.5 pounds (1.6 kg). There are no cables to snag on furniture or heavy modules to hang over your shoulder and cause fatigue. As the author of this article, I have tried to be completely objective on the design issues of the NLR as they relate to its selection and use. As the general manager of REI, I am, of course, an Orion supporter. Nevertheless, I hope that you have found this article interesting as part of the discussion on the problems of NLR.
Translated by S. F. Kornilov