Many radio amateurs consider a directional antenna at 7MHz to be a difficult goal requiring a tall antenna tower and a lot of aluminum.
Pokiaľ je dostatok priestoru, ponúka sa iné riešenie v podobe „zabudnutého“ 2-elementového inverted Vee beam-u. Many radio amateurs know and use the classic inverted Vee antenna. Everyone who has made it will probably confirm that it is an easily manufacturable and functional antenna. Adding one element creates a two-element fixed directional antenna.
You will find out in the article
Video: test 2-element inverted V beam 7MHz (40m)
Anténu pritom dokáže postaviť jediná osoba a cena je veľmi nízka. The video shows the first RX test after completion. The comparison took place in the afternoon hours. The second antenna is a 1/4 vertical on a dimensional metal roof, which works very well. It can be heard that DL/SP/I stations are significantly stronger on the beam, while UA almost unchanged - which is caused by the front-to-back ratio of the antenna. Of course, a significant difference is also caused by different polarization and vertical radiation angle of the antennas. Also note the change in background noise level.
Test in CQ WW SSB contest
Anténa prešla aj náročným testom v podobe CQ WW SSB conteste. With 100W, it helped break through pile-ups, for example on KP2, VP2M, VP5, YN, 6Y, KP4, V2, HK, PJ4, etc. Laci OM/HA6NL worked 17x YV with it one ordinary morning. Z tunajšieho QTH je to pritom najťažší smer úplne zakrytý horami…
RX comparison of 2el. inv.V beam 7MHz and 1/4 vertical antenna
Dimensions of 2el. inverted Vee beam antenna on 7MHz
Antenna construction
The antenna can be constructed in two ways: as a suspended or carried. In the first case, the support cable needs to be stretched in the direction of radiation. The carried antenna has the tops of the elements attached to supports. It is only on individual preferences which method is more suitable. Dôležitým faktorom je výška nad zemou. U mňa je to 13m, čo je asi minimum.
Popis 2-element inverted V beam 7MHz antény nájdete v publikácii 73 Vertical, Beam and Triangle Antennas (MFJ, 1992). The drawing also inspires a way to switch the direction, but I have not tried this option.
Simulation of 2-element inverted Vee beam antenna on 7MHz with a top height of 13m
Calculated course PSV antény
Comparison of radiation patterns of three antennas at 7MHz at the same height: half-wave dipole (red), 2-element inverted V beam 7MHz (blue), moxon antenna (black)
Simulation of 2-element inverted V beam 7MHz in MMANA programe ukazuje tieto výsledky: zisk 3,3dBd, F/B pomer 9,8dB a impedancia v rezonancii blízka 50ohm. The popular HB9CV has better properties (gain 4.1dBd and F/B approx. 20dB), but is it feasible?
I realized the carried 2-element inverted V beam 7MHz using combined dural-glass-fiber poles. First, we make the radiator with a center insulator and connection to the coaxial cable. We attach it to the pole, raise it, and anchor the pole. The ends of the radiator are raised by a thin climbing rope and stretched to the attachment points so that the inverted Vee at the top has an angle of at least 100°. We fix the wire to the director on the second pole, raise it, and anchor it.
2-element inverted V beam 7MHz after completion
Detail of poles and anchors of 2-element inverted V beam 7MHz. In the case of two or more people during construction, the system's stability can be increased by adding a delineating 6.22m rope to the antenna tops and anchor ropes from the pole tops in front of and behind the antenna
Setting up 2-element inverted V beam 7MHz
Výhoda tejto relatívne malej výšky je aj v tom, že anténu môžeme doladiť priamo zo zeme, len uvoľnením ramena prvku. The length of the elements is adjusted fundamentally to preserve their function in the antenna, i.e. the director is 4.8% shorter than the radiator.. Naladenie nie je komplikované, je však trocha prácne. Veľmi užitočným pomocníkom je antenna analyzer.
Measuring 2-element inverted V beam antenna at 7100kHz, Z=46ohm +/-j0ohm
Measuring 2-element inverted V beam antenna at 7030kHz, Z=39ohm +/-j0ohm
Measuring 2-element inverted V beam antenna at 7160kHz, Z=62ohm +/-j33ohm
Possible improvements for 2-element inverted V beam 7MHz
There are several possibilities for improvement. It is advisable to include in the feeding point balun 1:1. Asi najhodnejší je W1JR balun, which can be easily made at home in good quality and properties. Another option is the already mentioned change of antenna direction by extending the director to the reflector. It also offers the addition of another element and the creation of an even more profitable antenna.
2-element inverted V beam 7MHz made my favorite from the 7MHz band. Won't you join?