Multi-band loop antenna option
Many years of experiments, the authors showed that in the range of 160 m quite reasonable efficiency loop antenna with the perimeter, close to the wavelength. Despite the relatively low for this range the height of the suspension, usually not exceeding 20...25 m above the ground, such antennas work well as when intra-Union relations, and in the conduct of DX QSO. This design though simple to produce, but occupies a large area. So naturally desire to ensure its work and on other bands, even as a subsidiary. It should be expected that the efficiency of the antenna by increasing the frequency will increase. However, the direct use of the loop antenna is made for the 160-meter band, it is not possible because of the multiplicity of frequencies in the Amateur bands. The table shows the SWR (option 1) antenna in the form of an equilateral triangle of copper wire with a diameter of 2.2 mm. suspension Height is 20 m. the plane of the frame horizontal and parallel to the surface of the earth. Power is applied and one of the angles of a triangle. In all cases hereinafter specified minimum SWR.
To optimize the matching of the antenna in several ranges, we used the method (and its proposed DL7AB), allowing you to customize to resonance at all LW bands a long wire antenna" and is described, for example, in . The idea is the following. To break the wire frame on the right and left of the point include power inductors, lengthening of the action which affects most strongly when they are in the antinodes of the current, and gradually decreases as the nodes of a current to the coils. Thus, there are two variables that are most strongly in real conditions affect the performance of the antenna on all bands: the first is the inductance of the coils, the second - place their inclusion.
Minimum SWR two options of antennas
Table 1 Range, m Option
antenna 8040 2015 10 I1,05 3,54,25 4,054,3 3,8 II1,1 1,11,5 1,31,55 1,05
In the same table (option II) indicated SWR on the band performed in a similar manner to the antenna. It was an equilateral triangle with an overall length of the blade 158 m, also located horizontally relative to the ground. Power was supplied by a coaxial cable with a characteristic impedance of 75 Ohms. In the place of its connection to the frame produced symmetrize (you can use any of the known methods) power supply circuit.
The authors tested two variants of balancing, which gives almost the same results. In the first case on ring (size CHH) of ferrite VC-2 wound 10 turns (spreading them evenly around the circumference) of the feeder. In the second case, a similar ring on the layer Lukashenka was wound 15 turns of two twisted lengths of the mounting wire mgshv-section of 1 mm To one end of the coil connected to the frame, the other feeder. In both cases, the coils were carefully protected from environmental influences.
Lengthening coils included in forming the angle from which it feeds the antenna, at a distance of 12 m from its top. Coil - frameless wound on the mandrel with a diameter of 45 mm and contain round 4 (step 8...10 mm) copper tube with an outer diameter of 3.5 mm. Establishing antennas start with the settings in the resonance of the entire system on the 160-meter band. For this purpose, the perimeter of the antenna was initially somewhat smaller (about 156 m) above, the excess in the form of loops left in the feed point. Changing their length, making minimum SWR in the middle of the range. Checking the value of this parameter in other ranges, if necessary change within a narrow range of inductance coils, shifting or expanding their turns. In the case where some of the HF bands fail to achieve a satisfactory SWR, you may need to slightly change the connection point of the coils that is done very simply by the method described in [L] in the "double square". For this purpose coils for the authors did plumes for setting, when you change the length of the coil which was moving on the leaf antenna. Plumes was a chain of insulators with a length of about 0.75 m, bridged by the conductor. By varying the length, changing the frame length for the coils. After this operation is necessary in the opposite direction to change the length of the loop at the feed point so as to maintain the resonance of the antenna in the range of 160 m.
However, as a rule, such a precise fit is not required, as evidenced by the repetition of a design under different conditions and from different materials. Almost after tuning the antenna to resonance at 160-meter range VSWR on all bands had a quite reasonable value. Moreover, as shown by experiments, the configuration of the frame are irrelevant, i.e. it can be a triangle, square or polygon. It is only important that when you configure all operations were carried out symmetrically, i.e. if you change the length, inductance or connection point of the coil, it must be done in both "branches".
Described antenna, the authors compared with some others. In the range of 160 m at a distance of correspondents 1,000 km, she gave a gain in the signal level is not less than one point compared to half-wave and wave dipoles and beam length of 106 m. For a more extended paths, the difference reached two points in comparison with the half-wave dipole and beam, and one point in relation to the wave dipole with an average height of the suspension to about 27 m. the ranges of 80 and 40 m were tested loop antenna of the respective ranges, dual band "INVERTED V", like w3dzz and whip at 7 MHz. The advantage over the first three antennas was evident at all the tracks, especially significantly (up to 12 dB), it was expressed in relation to the "INVERTED V" and like w3dzz. Estimated correspondents at the distance of more than 2000 km in the transition to a whip antenna, an increase in the signal at one point of the scale 5.
Of greatest interest is the work of such a framework on HF bands 14-28 MHz. Almost always when changing from a dipole or its modifications on this antenna on any band, the signal was increased maximally by two points. When conducting DX QSO in certain conditions, not always, but there was a slight increase in signal compared to when he used a quarter-wave pin.
Using "electric lengthening", you can construct a loop antenna with a resonance at a frequency within 3,7 3,8...MHz, which is working well and all multiples of the higher frequency ranges.
Authors: G. Bolotov (UA3QA), P. Zemaitis(UW3QR); Publication: N. Bolshakov, rf.atnn.ru