The Basics of Hardware-Assisted Radio Path Efforts Using Universal Radio Test Set
Чегодаев Н. И. The Basics of Hardware-Assisted Radio Path Efforts Using Universal Radio Test Set // Молодой ученый. 2012. №7. С. 45-48.
According to the Russian Federation stable development by the year of 2020 conception published by economical security centre  there is a necessity of reliable telephonic services for rural inhabited localities. This task also demands a decision with a reasonable price and adequate functionality. In present conditions there are several limitations, which are the following:
1) There is no direct access to the wired telephonic lines within the borders of rural location;
2) We have not opportunity to use the standardized wireless equipment such as Wi-Fi modules and IP-Telephony or cellular communication systems, because of its incorrect and unstable job processing in a given location conditions;
3) We can not use a satellite services due to its maintain and acquiring expenses.
One of the most adequate solutions would be exploitation of a subscriber system of radio access, such radio extension devices. The essence of radio extension unit developed by the author of this publication is described in the appropriate article . There is only short description quoted hereafter.
The radio-extender device designed for purposes carrying the nature of wired telephonic line over the duplex radio path with the feature of conversation retransmitting. As distinct from counterpart analogues the device designed without any signal preprocessing, which could lead to malfunction and, possibly, to delay due to digital process mistiming in certain circumstances. The radio-extender device includes two opposite modules: the basic one and the subscriber one. This two modules are submitted to embody the unit as the whole. The subscriber module connects to an ordinary phone, which represents the control console for the subscriber and maintainer purposes, such as line selecting. The place of the basic module locates near the wired telephonic line spot for transporting its options, standard signals and calls as it is to the subscriber’s phone. The subscriber module should be placed in the geographical point, where wired telephony (or IP-telephony and the satellite communications as well) is unavailable, but in needed to be. The radio-extension unit uses dual-tone multi-frequency signaling as the key part of its functionality and allows multiple wired lines to be attached to the main module. The radio-extender uses standardized transceivers and ordinary telephonic apparatus as the parts of it, so, it makes possible to reject any special midterm converting devices, which widely used in counterpart analogues. The radio extension unit is patented .
The radio-extender had designed to include two possible operation modes: the outgoing one and ingoing one. In outgoing mode the operator (or, possibly, the subscriber) takes up a hand-set and determines which one telephonic line to use with help of a keypad of an ordinary phone. Thereafter, he can enter desired phone number. Wired line selection code (as the DTMF code in a lower frequency) applies to security identification between the main modules of the device, at the same time. In ingoing mode the basic module accepts call form one of the wired lines attached to it and specifies its number (in the terms accepted between the modules) to be transmitted to the subscriber module afterwards. If subscriber prefers to open channel to communicate with his or her abonent, he must take his hand-set and stay on hold. The radio-extension unit will keep the radio path and virtual conversation path alive automatically, within the call duration .
According to the Essence of Communication Theory by Richard Read [4, p. 22], one of the basic models of interconnection system includes the following parts. Source encoding device transforms initial signal to the electronic form and as counterpart there always exists a signal decoder to rebuild the original signal as it is. There always transmitter and receiver, which in our case presented as standardized transceivers, and between them there always located radio-channel or radio-path . Apparently, there is a radio path between the modules (interconnected by transceivers), and as a vital part, it needs to be entirely adjusted and its options must be all tested. So, before someone will pass to selecting and purchasing transceivers, he should investigate possible useful and adverse features of the radio path on a certain radio band.
Author of this article possesses an access to various ranges of devices, but most of them seem to be unhandy, because of it embarrassing size and encumbering weight. Most of this devices (such as oscilloscope) bears only one function with all this weight and size travel restrictions, and radio-path studies are supposed to be on open air afar from any civilized facility, as people say: “on a open cornfield”. So, the radio test set 2965 by Marconi Instruments has chosen. This all-in-one apparatus is still a heavy cargo, but at least it includes more than one radio-path test . Let us describe its functionality and the experiments, which we get through, in this publication.
The sort description of the apparatus in accordance to its manual  is quoted below.
The Radio Test Set 2965 provides a comprehensive measurement system for all types of mobile radio testing applications, including personal mobile radio (simplex and duplex) and cellular systems. It is suitable for making high performance radio system measurements in research and development, production and maintenance.The radio test set includes a high-performance, full-span RF spectrum analyzer with tracking generator is provided. This has features to enable component and sub-unit testing in addition to precision transmitter measurements. A 20 Hz to 40 kHz AF spectrum analyzer is provided to ensure total measurement capability. The large, bright display has soft keys at each side and beneath it. With the logical layout of the dedicated keys, this allows the many types of measurements of which the test set is capable to be carried out quickly and easily. An important operating feature is the ability to use several forms of automatic control and interfacing standards. These include IEEE 488.2 and RS-232 remote control as well as a parallel printer port [5, p.1-1].
Let’s consider the main modules of the package of the Radio Test Set, closely.
The apparatus includes a high-performance signal generator with an oven-controlled crystal oscillator reference which has an ageing rate of less than 2xl0-7/year. It has a fast switching speed and a usable output up to 1.1 GHz. The maximum output is +13 dBm with an accuracy of 1.5 dB.Studied device includes three modulation and audio sources, which can generate signals between 20 Hz (modulation) or 1 Hz (audio) and 20 kHz in addition to signaling tones and data. These can be combined to produce a single source with a range of 1 Hz to 100 kHz. In a set of available features there is a broadband power meter, which is adequate for measurements over the range 1 mW to 150 W with ani accuracy of 7%.The selective power meter included to the set makes selective power measurements possible with a sensitivity of -90 dBm [5, p. 1-1]. The radio test set allows duplex operation for simultaneous measurements on a transmitter and receiver with no limit to the frequency offset between. Device features allows it to handle up to 50 W continuous powers on its connectors and 150 W for a short periods of time. Fast audio analyzer of the device allows quick test execution for the signals up to 40 kHz [5, p 1-2].The radio-path under analyze includes transceivers as a parts of its hardware configuration. Positions under test are transmitter module testing, receiver module testing and transceiver duplex mode testing. The following analyses list includes power and frequency tests, spectrum analyze, modulation and oscilloscope probing. Transmitter test mode radio test set takes its role as a receiver so its measuring features includes the following:
1) The transmitter frequency (or frequency
offset) and power;
- 2) The modulation type, frequency, deviation or depth and distortion and/or noise.
The radio test set provides an AF signal for transmitter modulating. One of the three generators or a wide range generator could be selected manually. There are seven different stages of display, which one can utilize in this mode[5, p. 3-5]:
1) Primary with bar charts;
- 2) Primary with oscilloscope;
- 3) Primary with spectrum analyzer;
- 4) Primary with modulation analyzer;
- 5) Expanded oscilloscope;
- 6) Expanded spectrum analyzer;
- 7) Expanded modulation analyzer;
- 2) Primary with oscilloscope;
In receiver test mode, the radio test set pretends to be a transmitter and provides a modulated signal to a receiver. There are three modulation generators and the option of using an external generator. Each frequency and level is set independently and each generator can be enabled or disabled. The RF frequency and level and modulation frequencies and deviations or depths can be increased or decreased by previously entered increments. The 2965 also measures the level, frequency and distortion and/or noise of the AF signal that has been demodulated by the receiver. This mode allows five different stages of display as follows [5, p. 3-7]:
1) Primary with bar charts.
2) Primary with oscilloscope.
3) Primary with audio analyzer.
4) Expanded oscilloscope.
5) Expanded audio analyzer.
Duplex test mode determines the radio test set on simultaneous functionality. It causes the device to be both transmitter and receiver. Functionality of the device is similar to the transmitter test and receiver test mode, except the display is divided to the appropriate parts: the left-hand part shows the results of receiver testing and right-hand demonstrates the transmitter analyzing data. There are thirteen different view modes according to this mode description [5, p.3-8]:
1) Primary display mode with bar charts;
2) Seven duplex test in transmit mode views similar to the transmitter test mode;
3) Five duplex view modes.
So, in the transmitter testing mode, by measure conditions adopted by the developers of the device, we should combine the connector of transmitter radio-frequency input and the radio-frequency socket of the device and to finally determine the essence of the connection to the device internal circuits and processors we will select the appropriate connector with the button labeled with “rf select”. Indicator will mark the socket. As for us to set the main testing mode so we must press the button labeled with “Tx Test” test, and then the apparatus will automatically set to the strongest frequency and display the bar charts of it. To set required frequency, one must use a labeled button sequence as follows: “Tx” to select the on-screen text-box containing the frequency definition, then a “Freq” labeled button must be used to determine a text-box change and then to finalize his selection user must click the button with the “Inc” text. Frequency value can be entered by clicking the buttons of the data group, which represents as a set of numbers (number pad) similar to the personal computer numpad. In a current mode just after the frequency definition the author possessed information regarded to particular qualities of spectrum parts of the transmitter, which is located by the other side of radio path, in terms of our publication about telephonic services for remote objects problematic  the basic module transmitter, which interconnected basic module accepts direct connection to the wired telephonic lines. In this mode an adequate modulation level is defined and appropriate levels of low frequency signal is set to fulfill the restrictions imposed by emulating over the radio-path telephonic line [5, p. 3-19]. Meanwhile, on the other side of the imitating radio-telephonic system the assistant connects the receiver radio-frequency input connector to the apparatus corresponding connector. Similarly to the tester described above he selects a connector type by the button labeled “RF select”. Then, as to set the testing device to the receiver test mode, which means the role of a transmitter one must press the button labeled as “Rx test”. In this mode a radio-frequency generator must be set by the radio-path features researcher or the tester to allow the frequency to be entered then. Then, as to the transmitting issues one should set-up a modulation generator, which could be selected from listed three positions or can be set as external. By the data provided by this mode and with the help of the tester possessing the apparatus in a mode described above the two specialists can obtain a useful information regarded to signal-to-noise characteristic, audio frequency value and obtain an oscilloscope graph of studying signal, which is cruising in an imitating radio-telephonic system radio-path [5, p. 3-38]. By obtaining and analyzing this information, they can decide about the possibilities of a further development and deployment for the radio-path system for radio-extender . Indeed, the radio extension unit works in a full-duplex mode itself by information provided by the article regarded to telephonic services for remote objects problematic , so this means that one should the possibilities of a duplex interconnection mode between the modules of imitating radio-telephonic system. In this case, one should perform the following connections: receiver radio-frequency connector must be plugged to the apparatus socket labeled as RF TNC socket; audio frequency connectors of both transceiver and radio test set must be interconnected; transmitter radio-frequency output connector and radio frequency N socket of the radio test set must be plugged up; audio input connector of the transceiver needs to be connected to the socket of audio generator of the apparatus. As required by the radio test set manual [5, p.3-47] on must press the apparatus button labeled as “RF select” to configure the sockets and the button labeled “Duplex test”. In this mode the tester could obtain the same signal characteristics as above, but for the duplex mode and decide which of simplex or duplex functionality are better in his case.
When the all appropriate tests are complete, it would be effectually to compare them with the data of mathematic model study results  as required by full-scale mathematic model test [7, p.36]. Alternatively, the results, which are provided by mathematic model, could be double-checked with natural test (the test within the rural countryside conditions) such as this. In other words, the natural test can be accompanied with theoretical mathematic test. Neither of the tests should be in introversion. Indeed, the obtained information is useful in case of radio extension unit deployment.
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