Antenna for alarm radiochannel
Automotive radiofrance devices operate at a frequency of 26,945 MHz. Radiozero contains two power - transmitting and receiving. In a transmitting unit consists of the actual autostorage with the necessary set of sensors, an encoder and a transmitter with an antenna mounted on the car. The receiving unit includes the antenna, receiver, decoder and a sound generator of the disturbing signal.
When the sensor is triggered autostorage transmitter emits a radio signal modulated pulse code generated by the encoder. A receiver with a decoder selects from the mass of signals the signal generator includes an alarm signal.
The use of speakers of the transmission, such as whip antennas in systems radiochannel car alarm is virtually eliminated because of the possibility of malfunction of the system when the mechanical damage is clearly visible and easily accessible protruding external antenna.
The range and stability of radiogenic systems is strongly dependent on the correct type of antenna-feeder system and the quality of its implementation.
Requirements for the radiation pattern and thus the antenna gain is defined by the fact that the location of the receiver in the horizontal plane arbitrarily, and the vertical is limited to a small angle between the earth's surface and are relatively low-spaced antennas. That is, the antenna pattern should be close to circular in the plane of the horizon and narrow vertically.
Since at low antenna positions relative to the earth's field at the receiving end has the nature of the interference, i.e. is the sum of direct and reflected fields from the earth rays is very important the choice of polarization of the radiation. Horizontal polarization depth of the interference dips more than when vertical. Therefore, in grassroots radio it is advisable to use vertical polarization .
Because the automotive antenna system radiochannel alarm is placed inside the conductive body of the car (usually near the Windows), its radiation pattern is significantly different from the chart of the same antenna in free space. This is because the radiating antenna will create currents on the conducting surface of the car body, and the radiation of these currents together with the actual field antenna generates the resulting chart.
The interaction of these two fields leads to the fact that in part of the space field is weakened, and in part increases.
In the long-wavelength plot УSW effective range different versions of slot antennas. Usually slot antenna is a narrow slit of length L/2, slotted at the plate, streamlined current. Approval of the slit space is performed by adjusting the slit width. Horizontal cracks polarization vertical radiation.
However, for that portion of the band slot antenna in a classic design bulky and structurally awkward. Therefore, it is advisable to use a wire analogues of plane type antennas [2, 4]. The excitement of such antennas is symmetrical cable through the cable, in connection with which such antenna is called a Daisy chain. To simplify power scheme is more practical to use a single transmitter is connected via coaxial cable [C]. Electrical lengthening the radiating part of the antenna is achieved with additional loops W1 and W2 and a capacitor C1 (Fig. 1). Capacitor C1 is included in the point l of the antenna corresponding to the maximum phase voltage that is equivalent to an increase terminal capacity elements. It should be noted that this antenna has a higher efficiency than whip with a lengthening inductors. Yet you can get a reasonable size of the plumes and the input resistance at resonance is close to 50 Ohms.
The antenna is similar to , made of wire MGTF 0,3. From the same wire made cables W1, W2. The conductors of the cables are parallel and close to each other. The antenna wire is placed under the rubber seal of the rear window of the cabin. Cables W1, W2 are folded three times along the length and along with the capacitor C 1 is placed in a dielectric tube that is attached to the strut of the fiberglass thickness of 1 mm Spacer is positioned vertically in the middle of the rear window and is fixed in the rubber gasket. Since shortening the capacitor included in the antinodes of the voltage at the transmitter power 1...2 W the amplitude of the voltage on the capacitor C1 reaches several tens of volts. This should be considered when selecting the capacitor type. Manufactured and tested two loop antennas with respect to VAZ 2107 and ZAZ 968 M (dimensions in Fig. 1 are shown in parentheses). The setting is made on a maximum radiation (minimum SWR) by rotation of the rotor of the capacitor C1.
The results of the test antennas in the form of a pattern on a sustainable level triggering autostorage in an open area shown in Fig. 2. The Daisy chain pattern made of antennas indicated by the number 1, and number 2 - chart circular loop antenna set "Signal-RK". The polarization loop antenna is vertical.
From Fig. 2 shows that the loop antenna located on the inner perimeter of the rear window inside the car, is not only hidden, but also provides a better range. Structurally, the loop antenna is simple, reliable, cheap and easily manufactured. When the loop antenna is not used for its intended purpose, it can be used as an effective receiving antenna УSW-range radio or a radio that eliminates the need to install an external whip antenna.
Author: E. Stakhov, Grodno; Publication: www.cxem.net