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Международный военно-технический форум Армия-2017

On “Benefits” of Low-Power Detectors

For a long time, virtually about twenty years, an active advertising and propaganda campaign has been conducted by Western and, unfortunately, Russian producers of special machines for support of low-power nonlinear junction detectors (NLJD). The power under discussion is 1.5 – 4 W, and often it is not actual radiated power, but equivalent isotropically radiated power, that is with account of the antenna gain, which increases the index many times. To see the scale of the disaster, consider this: 4 W NLJD is already classified as HIGH GAIN abroad. I would not name concrete brands, but they do propagate these low-power detectors and are seriously engaged in their production, using information cover in the form of several main points. The first point concerns ecology, first of all, the influence on the operator. A US website has actively scared people telling them that Russian or Chinese detectors are the most awful, as they can burn food.

 

Fig 1. Detail of a NLJD advertising folder.

The craftiness consists in manipulations with different physical notions - peak pulse power is indicated to evaluate Russian NLJDs, and it really makes up several hundreds of watts. For instance, the maximum pulse power of NR-900 EMS nonlinear junction detectors makes up 180 W (it is regulated by the operator). At the same time, the average radiated power, with account of radiation pulse ratio of 1500, makes up only 0.2 W, which is less than mobile telephone emission. Needless to say, work with such a detector is far less harmful than that with a continuous radiation detector, which constantly “warms” the operator with two-three watts of UHF energy. However, no one writes about this, the average power is never indicated as a parameter. What is the reason behind this – unwillingness to understand the physics of work, signal time structure or a deliberate profanation?

There is also another extreme in representation of the reality – it is expressed in a mild, naïve question: what for do we need detection range? As we work along the wall, the bug cannot be as far as half a meter from us, can it?

At the same time, talking about the detection range, one keeps in mind the detector power, which is, actually, right if we consider the radiolocation formula:

 

  • Pr —signal power at receiving antenna clamps;
  • Pt — power of the radio transmitter;
  • Gt — antenna gain factor;
  • Ar (sometimes S) — effective area (aperture) of the receiving antenna, Ar = G*λ²/4π, where G — receiving antenna gain factor, λ — wave length.
  • σ — radar cross-section (RCS) at this angle;
  • F — loss factor during signal propagation ≈ 1;
  • R — distance to the target;

Upon a closer view, this equation has such a parameter as σ - radar cross-section (RCS). It is worth paying special attention to it, since it is RCS which determines target “detectability”. Besides, the formula can be interpreted in the following way: power change is equivalent to RCS change. That is, by increasing possible radiated power, one can increase not only penetration depth, but also possibility of detecting a target with a small RCS. To achieve this, it is worth fighting for each decibel. Of course, detection range is a conventional measure, which simply helps compare detectors quickly and quite easily. It is enough to bring two detectors with the same target to the surface by turns; if they work in the same frequency range, the following comparison would be fair: the larger the detection range is, the better the device works. Detection range is just a convenient equivalent of the universal NLJD qualitative characteristic. According to the same formula, two-fold range excess is equal to 20 dB signal excess, which is two orders in target RCS. Two orders are serious enough to speak in favor of a higher power.

Another argument in favor of a powerful detector is the so-called effect of "destruction” (sometimes called the effect of “burning-off”) of decoy targets; in fact, there is no target destruction as such, but thin oxide layers change their characteristics under the influence of adequate power pulse radiation. The destruction effect has been many times confirmed by search experts who use detectors of NR-900 series.

The essence of the effect is as follows: when the operator detects a response and there is suspicion the response may be corrosive, one should keep the detector working in full power condition over this point for several seconds. If the signal fades, this is a corrosive contact: in the result of the influence, physical characteristics of the corrosive semi-conductor have changed. That is, presence of high power gives another tool for target selection, identification (decoding). There is no use carrying out these actions with low-power detectors – whether you hold them or not, the effect will be zero.

It is an important aspect, since decoding is a serious search problem familiar to all search experts. Using this, some producers readily assure in their ads that their detectors have become able to differentiate between a corrosive p-n junction and an artificial p-n junction, yet without explaining this miracle. In practice, there is no secure, stable result in this sphere. The only detector that somehow resolves this tasks deliberately is NR-900V (Vector). In this device, the automatic identification principle is analysis of response change depending on radiation power change. As is known, an artificial semiconductor shows such dependence in the parabola form. That is, when we change power by caliber, the response changes correspondingly; such a change may be calculated and formalized in the form of a certain conclusion – whether the semiconductor response was natural or artificial.. Decoding in this device is based on a real physical principle. This approach has given some hope for decoding probability, which is now larger than 50 to 50. A different matter is that Vector does not resolve this problem absolutely effectively. However, a test with more than 300 different targets, both corrosive and real, showed 70% of the correct detection results. Is this value low? Probably. But it is necessary to understand there are situations when correct decoding is hindered and is close to being impossible. For instance, suspended office ceilings contain steel wire, zinc coating, sometimes brass elements or something else. The contact between these components is so complicated that they often turn into a semiconductor in a pure form. The nature presents such a diode, which, actually, functions like a real diode. Here Vector is powerless. At the same time, two anti-parallel diodes make a good imitation of corrosion. Such facts show that claims about creation of a device capable of distinguishing between corrosive and artificial junctions are mere fiction.

As you see, there are weighty arguments in favor of a powerful detector. However, such a detector immediately imposes restrictions and poses problems for developers. For instance, we have a radiated power of + 53 dBm (200 W), antenna, as a rule, in one construct – both receiving and transmitting ones, isolation between them is 20 dB at best. In all, +53 dBm, 20 dB isolation together with the antenna and input of the receiver with a sensibility of, for instance, -130 dBm. Then it turns out the filter cannot be less than 90-110 dB, so that it would be possible to suppress out-of-band influence, otherwise the receipt will be blocked. That is why there is a need for suppression filters of 90-110 dB, which are expensive and technologically complicated, not to mention development… On the contrary, if we take a 2 W western-made detector of +33 dBm, isolation of 20 dB, a filter of 40-60 dB – all components combine well, everything is all right. Blocking is prevented, and such detectors are easily produced. Thus, on the one hand, such foreign producers criticize powerful Russian devices, shelter themselves behind concerns about ecology and negative impact on human, but on the other hand, they, actually, protect their interests, for the cost of low-power detector production is lower – cheap elements, no strict requirements for electromagnetic compatibility, blocking, screening. All problems with development and production become two times easier to resolve. Simple production makes it possible to rise the margin and offer flexible discounts so as to attract customers. The price can be easily lowered, since the prime cost is quite low. Thus, such producers express their alleged concerns about operators’ health and total inexpediency of powerful detectors, while their claims seem to be based on a commercial interest.

The question is whether their interest is purely economic. Analysis of production supplied to Russia from the West suggests there seems to be other interests in addition to business ones. To my mind, their goal is to prevent our search experts from being well equipped and from seeing too much during their search. It is worth remembering about another US device – a search portable spectrum analyzer, which has critical weaknesses and is made exactly to prevent a person from seeing something “unnecessary”. Perhaps, these search devices are made with special care about a person – to prevent people from worries and disappointments. Indeed, why be sad? A person just buys a beautiful convenient device, uses it, feels confident and satisfied. The same holds true for services: tranquility, calmness, comfortable work are guaranteed.

So, it turns out the producers selling such goods resolve two questions at a time: on the one hand, they ensure big gains from production sale thanks to its low prime cost; on the other hand, they do not intrude upon security service’s leisure. That’s the way it goes. It is sad enough, especially if we take into account the fact that such production may reach our public institutions.