Introduction Amateur radio Square DK7ZB yagi antenna 144MHz for portable

Square DK7ZB yagi antenna 144MHz for portable

Štvorča DK7ZB yagi antén 144MHz pre portable
Square DK7ZB yagi antenna 144MHz for portable

How to achieve maximum gain of portable antennas at 144MHz? Unlike single yagi, which would have to have a long boom and considerable height above the ground, so the group OK2VZE, OK2LOL, OK1ZHS v Alpe Adria contest 2008 used system 4×6 elementov yagi . That's it the antenna is also used by OK2R.

Single yagi / antenna system

The longer the antenna, thus it must be placed higher above the ground. If we consider profit of about. 16dBi, so it is achieved by a single yagi antenna with a boom around 8 meters. This represents a greater moment of the required force for rotation and, of course, a higher mast.

Advantages of a single yagi antenna

clean radiation pattern
absence of antenna merging
quick assembly of a split antenna

Disadvantages of single antennas

a narrow radiation pattern recognizable especially in the horizontal plane
higher mast required, at least 7 meters
demanding lifting and lowering of the mast with antenna
more torque required to rotate the antenna

Directional characteristic and gain of a single yagi antenna in free space
Directional characteristic and gain of a single yagi antenna in free space
Directional characteristic and gain of single yagi antenna in height 7 meters
Directional characteristic and gain of single yagi antenna in height 7 meters

Antenna system with a profit of approx. 16dBi can also be achieved by a system of two, because of, four or more antennas. A larger number of antennas is used as a fixed antenna system with a wide radiating lobe.

Advantages of a system of two antennas on top of each other

shorter antennas with a boom around are sufficient 3,5 meters
the radiation pattern in the horizontal plane is wider than in single yagi
the torque for rotating the antenna is lower
higher mast required, at least 7 meters

Disadvantages of a system of two antennas on top of each other

the need to combine two antennas
demanding lifting and lowering of the mast with antennas

Directional characteristic and gain of two yagi antennas YU7EF in free space
Directional characteristic and gain of two yagi antennas YU7EF in free space
Directional characteristic and gain of two yagi antennas YU7EF in height 8 meters
Directional characteristic and gain of two yagi antennas YU7EF in height 8 meters

Advantages of a system of three or four antennas on top of each other

shorter antennas with a boom around are sufficient 2,2 meters, or. 1,5 meters (four antennas)
the radiation pattern in the horizontal plane is wider than in single yagi

Disadvantages of a system of three or four antennas on top of each other

higher mast required, at least 8 to 10 meters
demanding lifting and lowering of the mast with antenna
the need to combine three antennas
antennas with a length over 1,5 subways must have a split boom due to transportation inside the car

Advantages of a system of four antennas in configuration 2×2 (H-čko)

shorter antennas with a boom around are sufficient 1,5 meters
such antennas can be transported inside a car
a lower mast with a height of about is sufficient 5 meters
easier mast lifting
acceptable torque for rotation

Disadvantages of a system of four antennas in configuration 2×2 (H-čko)

use of H-construction
the need to combine four antennas
the horizontal plane radiation pattern is narrower and less clear than in other antenna or single yagi configurations

Directional characteristic and gain of four yagi antennas DK7ZB in H configuration in free space
Directional characteristic and gain of four yagi antennas DK7ZB in H configuration in free space
Directional characteristic and gain of four yagi antennas DK7ZB in H configuration in height 5 meters
Directional characteristic and gain of four yagi antennas DK7ZB in H configuration in height 5 meters

TIP – countersunk nuts

Petr OK1FIG used countersunk nuts in its construction, thus achieving the lower part of the boom antennas without larger protrusions. In addition to aesthetics, this has the advantage of not catching antennas when inserted into the car

Choice of antenna options

I build antennas in one person. Examples show how larger antennas can or cannot be lifted antenna lifting. However, sometimes the wind blows and the higher mast can be difficult to lift anyway. I preferred the construction of four shorter yagi antennas in configuration 2×2 (H-čko) also because of that, that such antennas can be transported without disassembly inside a car.

YU7XL, S53WW, DG7YBN, G0KSC, DK7ZB oil

Such short antennas are not described YU7EF, the shortest model is 6 elemental yagi. Design S53WW is interesting in terms of profit, but it requires a loop dipole which is more difficult to manufacture. The antenna is also more sensitive to the surrounding environment and the advantage of production.

The short oblong antennas of the YU7XL are interesting in terms of boom-to-gain ratio. However, the spatial design complicates the transport of the antennas as well as the assembly of the square.

Remaining DG7YBN designs, G0KSC, DK7ZB yagi antennas are at the individual preference of the radio amateur. I chose the design from DK7ZB. Antenna with length 1,5 subway has 5 elements and a profit of approx. 8,4 dBd. The impedance is 50 Ohm. Power is via so-called. coaxial cable balun.

TIP - use of square profiles

Using a profile 20 x 20 mm for the construction of the supporting H-tag and individual boom antennas, their connection will be simplified. This is possible with flat T-couplings with dimensions 120 mm x 54 mm x 19 mm (purchased in OBI)

TIP - use a cordless screwdriver

Assembly and disassembly of the H-piece and connection of antennas is accelerated by a cordless screwdriver. Stainless steel countersunk Allen screws are used 7991 M5x30 and standard stainless steel hexagon nut M5.

Production 5 element antennas DK7ZB yagi

The production of antennas itself has been described many times. The elements are fastened to the boom in a black polypropylene holder using an M4 screw and countersunk nuts. They have an average 10 mm, boom is out of profile 20 x 20 mm.

RG-174 coaxial cable and plastic tubes for ballast baluns
RG-174 coaxial cable and plastic tubes for ballast baluns

The radiator is mounted by cable glands in boxes Z54 = KP 45 (Z54J). It's inside choke balun made of Belden coaxial 8216 RG174 / U. Its length is 34,3 centimeters, which includes the coaxial cable shortening factor (0,66). The length is measured between the ends of the braid - the leads to the radiator and the connector do not count towards the length, but they should be as short as possible. An N-connector is used, which is connected to the boom.

Measurement 5 element antennas DK7ZB yagi

Measuring one 5 element yagi antenna DK7ZB
Measuring one 5 element yagi antenna DK7ZB

The antennas thus assembled were measured under temporary conditions with such a result

The third antenna was slightly tuned to a different shape of solder lugs connected to the radiator.

Measurement of assembled square DK7ZB yagi antennas 144MHz for portable on mast 5 m

PSV 5 element DK7ZB yagi antennas
PSV 5 element DK7ZB yagi antennas
PSV 5 element DK7ZB yagi antennas in a narrower range
PSV 5 element DK7ZB yagi antennas in a narrower range
Measurement of a system of 4x5 elements DK7ZB yagi
System measurement 4×5 elements DK7ZB yagi
Measurement of PSV system of 4x5 elements DK7ZB yagi
PSV system measurement 4×5 elements DK7ZB yagi

Photographs from the production of the DK7ZB yagi radiator box and ballast baluns

TIP - filling the box with PUR foam

The idea comes from Vlad OK1VPZ. In addition to improving the flow resistance of the box, the radiator is also more firmly fixed.

H-carrier design for four yagi antennas

H-čko also uses it profile 20 x 20 mm a flat T couplings. They are also used to connect boom antennas. Here it is good to use an angle, so that the antennas are held exactly. Don't forget them Mark, otherwise it could happen, that you swap the individual antennas and the place in the phase will be in antiphase.

Production of H-carrier for DK7ZB yagi antennas
Production of H-carrier for DK7ZB yagi antennas

Two threaded loops are used to attach to the mast.

Price of a square DK7ZB yagi antenna 144MHz for portable

Indicative material budget

profile 20 x 20 mm in length 8 meters 80 €
tubes 10 mm in length 20 meters 30 €
element holders 16 €
T couplings 16 pieces 6 €
boxes Z54 12 €
N connectors 16 €
Belden coaxial cable 8216 RG174 / U 3 €
PUR worth 4 €
nut, screws, soldering lugs 13 €
combine four antennas 70 €
RF240 phasing cables with N connectors 40 €
TOTAL: 290€

I used the material for the construction, who had mostly at home, several prices are therefore only indicative for those interested in the implementation of a similar antenna.

Practical experience with square DK7ZB yagi antennas 144MHz

Assembly and disassembly of antennas in field conditions is very good. Lifting the mast in one person is not a big problem.

Measurement 5 element DK7ZB yagi antennas
Measurement 5 element DK7ZB yagi antennas
Measurement 5 element DK7ZB yagi antennas in temporary conditions
Measurement 5 element DK7ZB yagi antennas in temporary conditions

The antenna was practically compared with 8 element DK7ZB yagi, which has the declared profit 12 dBd. The system has a theoretical gain 14,2 dBd (without taking into account the losses in the phasing cables and the combiner).

Four 5 element DK7ZB yagi mounted on a folded mast
Four 5 element DK7ZB yagi mounted on a folded mast

 

In operation, it clearly outperformed the single yagi despite the handicap of power supply with a worse and longer coaxial cable. I also appreciated the more directional antenna when receiving as much 8 km away is OM3CQF, 12 km OM3Kii a 16 km OM2ALD.

Square 5 element DK7ZB yagi antennas
Square 5 element DK7ZB yagi antennas