RADIO WORKS - VRD10 - 10 METERS HALF WAVE HORIZONTAL POLARIZATION DIPOLE + QUARTER WAVE VERTICAL RADIATING LINE
TECHNICAL SPECIFICATIONS:
- LENGTH OF THE HORIZONTAL DIPOLE: Half-wave (about 5 m total)
- LENGTH OF THE VERTICAL LINE: Quarter wave (about 2.5 m)
- POLARIZATION: Horizontal + Vertical
- MATCHING LINE: 50 ohm coaxial cable
- NEED OF TUNER: No
- APPLICABLE POWER: 1500 W
- TYPE OF BALUN EMPLOYED: Dedicated Line lsolator, depending on the band
DESCRIPTION OF "VRD" TYPE OF DIPOLES
This special type of dipole is very interesting for all those who want to work, in addition to local stations, even the DX with few complications and very low cost.
The "VERT" effect has previously been experimented with Carolina Windom, another leading antenna of Radio Works.
Taking the cue from this antenna, Radio Works has produced dipoles optimized for each single band and consisting of the classic half-wave dipole powered in the middle by a vertical radiating line of a quarter-wave length, isolated from the coaxial line by using a Line lsolator, also modified for the purpose and bandwidth optimized.
The result has been remarkable as to the possibility to work DX signals, that is to say long distance.
So why are we still producing simple dipoles?
The explanation lies in the fact that the dipoles are very good for high radiation angles, as well as for short and medium distance contacs, if properly installed.
On the other hand, VRD (Vertically Radiating Dipoles) dipoles have an extremely low radiation angle, due precisely to the prevalence of vertical polarization.
The maximum current point of the vertical radiator, however, is located at the top, at the junction point to the horizontal section, and not at the bottom, where it joins the coaxial line, with the undoubted advantages of moving this point of maximum current at the top, far from the earth and its ohmic losses.
A further advantage also derives from the fact that a horizontal dipole will have a figure-8 radiation pattern, with the maximum radiation perpendicular to the conductor and the minimum radiation in the direction of the extremities.
VRD, on the other hand, has an omnidirectional radiation pattern, with an extreme advantage at low angles.
Therefore, during the hours when the propagation is short the dipole VRD and the horizontal dipole can tend to equalize, but when the propagation skip is longer and the angle required to work the distant stations is lowered, the advantage given by the low angle vertical radiation component of the VRD compared to the conventional dipole becomes drastic: an average advantage spanning from half a point to 3-4 S-meter points, which means from 3 to 18-24 dB of difference!
Obviously we speak of dB of advantage referred to the signals coming from low angles, which on the low bands means the difference between working or not working a DX station.
But even at higher angles of radiation generally the VRD exceeds, even if slightly, the horizontal dipole, which can compete with the DX signals in 80 meters only if it is suspended at 40 meters from the ground, while for the VRD for the same band an excellent DX performance is already achieved at 20 meters from the ground.
Even if there is not enough height to keep the entire vertical section of the antenna vertical, it can also be folded into the terminal part of the antenna.
The VRD can also be mounted as Sloping Dipole, with slight modification of the radiation pattern, if the available space or supports are not adequate: the efficiency will be roughly similar to that of an inverted-L.
No tuner is required as the S.W.R.is very low, generally better than that of a conventional dipole located in the same place and at the same height.