All measurements and experiments were carried out with a Voxtel MR 350 radio station.
Parameters of the original helical antenna:
Spiral inner diameter: 3mm
Wire diameter: 0.5mm
Number of turns: 18
By calculation, it was found that the maximum calculated inductance of a helical antenna is 0.28 μH.
L = D2 * n2/(45 * D + 100 * l), µH
D = 0.3 cm - inner diameter of the coil
n = 18, number of turns
l=0.9 cm - total winding length
You can reduce the inductance of a helical antenna and thereby increase its resonant frequency by increasing the interturn distance, that is, by stretching.
Using a field strength indicator, it was possible to establish that the resonant frequency of the helical antenna of the radio station was much higher than the operating frequency, that is, 446 MHz.
It was also possible to identify a strong influence on the resonant frequency of the antenna from surrounding objects.
When I brought my hand to the antenna, that is, introduced a capacitance into it, its resonant frequency decreased and at some point even reached the operating frequency, after which it further decreased.
To simplify the setup of the antenna, a new sample was made, consisting of two inductances connected in series.
For the needs of civil radio communications in Russia there are 3 frequency range:
- 27 MHz (CB), permitted power – up to 4 W. At this frequency, you can use radios with any type of antenna (compact, car, stationary).
- 433 MHz (LPD). Allowable power – maximum 0.01 W. Walkie-talkies with compact integrated antennas are used.
- 446 MHz (PMR). Allowable power – maximum 0.5 W. Communication is carried out using radio stations with compact integrated antennas.
In reality, many factory radios in the PMR and LPD ranges have a power of up to 5 W. Devices with a power of up to 0.01 W in the 433 MHz frequency range, as well as up to 0.5 W in the 446 MHz frequency range do not need to be registered. Roskomnadzor is engaged in identifying radios that do not comply with power standards established by law. The list of radios subject to registration and the registration procedure are determined by the relevant legislative act of the Government of the Russian Federation.
Upon completion of registration, the owner receives a Certificate of Registration. Stations without exit to telephone network are not subject to certification.
The wavelength in radios of the CB range is 11 m. The radio wave can overcome an obstacle of half the wavelength, and radio stations in this range are optimal for use on rough terrain. The radio wave will go around any uneven terrain or group of trees 5-6 meters in diameter. With similar electrical parameters, they guarantee a longer communication range. At 27 MHz, electromagnetic interference of industrial origin or intermodulation is possible. The reason for this is the air congestion in cities. When using radios with compact antennas in a city or near a city, the communication range is unpredictable.
In this range, “long-distance passages” are not excluded, that is, communications can travel very long distances, including the formation of a “radio echo” (its own signal that has circled the planet) as a result of re-reflection from the ionosphere.
With high solar activity, the likelihood of “long-distance travel” increases. This negatively affects the range and quality of short-range communications due to additional intermodulation interference.
The wavelength of popular radio stations with frequencies of 433 and 446 MHz is approximately 0.7 m, for this reason it is not suitable for rough terrain or forests. A radio wave is not able to bypass even a 35-centimeter tree trunk. But radio stations at 433 and 446 MHz are optimal for urban environments, since there is little atmospheric noise and industrial electromagnetic interference in this range.
The communication range is influenced by the most various factors, among which:
- electromagnetic interference. LPD and PMR radios tolerate them better than CB, since the level of industrial and atmospheric interference on the 433/446 MHz bands is much lower than on 27 MHz. Therefore, in the city, the communication range of LPD/PMR stations guarantees better communication range.
Wave effects (diffraction, interference). They make it possible to overcome obstacles smaller than half the wavelength. This leads to the fact that the signal becomes inhomogeneous at distances comparable to the length of the radio wave. On rough terrain or in the mountains, SV radios work better than others.
As a result of reflections from the ionosphere, “long-distance passages” are possible for CB radios. For stable two-way communication, a good antenna and a certain state of the ionosphere are required. In the LPD/PMR bands, “long-distance travel” is not possible.
Absorption of radio wave energy by the surface of the earth and trees. Absorption increases with increasing wave frequency (SW wins).
Antenna efficiency is important for walkie-talkies.
Pin-type ones can be called effective vertical antennas a quarter or more wavelength of the signal. The following are optimal for quarter-wave antennas:
§ NE – 2.78 m;
§ LPD – 17.3 cm;
§ PMR – 16.8 cm.
The geometric size of the antenna is considered. But it can be shortened while maintaining the electrical “length” with an extension coil.
If a shortened antenna is made narrow-band, with a large resonant gain in frequency, this will increase the efficiency of compact antennas, but only when operating in the narrow frequency range for which it is tuned.
For shorter-wave LPD and PMR radios, the antenna does not need to be significantly shortened, but for long-wave CB, an antenna shortened by up to 20 times reduces the radio communication range. Such walkie-talkies work well only with long antennas, but are inconvenient to use.
It is impossible to say for sure which range is better.
Each civil communication range has its own advantages and disadvantages, which are visible in different conditions. When choosing a range, be guided by operating conditions.
For suburban communications, over long distances in the forest or on rough terrain, it is better to prefer the SV radio station. Better connection in the city, in particular, inside a reinforced concrete building or vehicle (without an external antenna), LPD/PMR radios will be provided. If it is not the range that is important, but the comfort of wearing and size, choose LPD/PMR. To transport a walkie-talkie abroad, it is better to take a PMR. If you need to contact professional or amateur radio stations, it's worth a try walkie talkies LPD, since PMR channels at 6.25 kHz are shifted around 446 MHz, and the majority of amateur and professional stations do not have a segment of 6.25 kHz.
Several collinear antennas are described below, all of them are designed to be made of aluminum wire with a cross-section of 6 mm square (recloser wire from which the PVC insulation has been removed). Aluminum wire was chosen because aluminum, unlike copper, is more resistant to corrosion and has slightly lower electrical conductivity, i.e. An antenna made of aluminum works no worse than one made of copper, but does not rot under our acid and alkaline rains.
All antennas are made according to the “J elbow and phase-shifting loops” scheme and are bent from a single piece of wire. By default, the antennas are calculated for PMR 446 MHz, but can be easily converted to LPD 433 - 434 MHz.
The width of the short-circuited line forming the J elbow for all antennas is 20mm, the length is also the same 1/4 wavelength or 168mm, only the feeder connection points are slightly different.
Collinear antenna 2 x 5/8 plus 1/2 L
Collinear antenna 3 to 5/8 plus 1/2 L
Collinear antenna 4 to 5/8 L
Collinear antenna 4 x 1/2 L
The antennas are adjusted by selecting the location where the feeder is connected to the J elbow and by slightly trimming the last, topmost element, since only this element is subject to the shortening factor.
The antennas together with the J elbow, as mentioned above, are bent from a single piece of wire; the “counterweight” going down from the J elbow is mounted later using the twisting method.
When assembling the antenna, all distances are measured from the center of the wire, and not from the boundaries, the measurement accuracy should be no worse than 1 mm.
Please note that the measurement error in the elements of the main antenna fabric is cumulative, that is, if when bending the first knee, counting from the bottom of the J knee, we made an error by +2 mm, then we can correct this by making the length of the phase-shifting loop that follows it less by 2 mm. If the error there is +2mm, then the total error will be +4mm, if we make an error by another 1mm in the next leg, then the total error will already be +5mm, which will inevitably lead to a drop in the antenna gain as a whole at the design frequency.
So that those who want to repeat the antennas can imagine how to bend the antenna, here is a photo of a ready-made antenna 4 x 1/2 L on PMR: 
When connecting an antenna, it is desirable that the feeder be diverted at least 1/2L at an angle of 90 degrees to the antenna surface.
The collinear antennas themselves, made of wire with a cross-section of 6 mm square, do not have structural strength and are not able to support themselves, so they are secured to a plastic fishing rod with polyethylene ties. As tests have shown, the plastic of Chinese fishing rods is radio transparent and does not affect the parameters of the antennas.
Phase-shifting loops can be made in another way - in the form of 1 turn, with such a diameter that its circumference corresponds to the length of the phase-shifting loop.
If it is necessary to recalculate one of the presented antennas at 433 MHz, then all its elements are lengthened in proportion to the change in frequency, that is, the length of each element, including the lengths of the J elbow and phase-shifting loops, must be multiplied by 446/433 or 1.030023094688222.
Loading...
