WRTC-2010 is for the first time Field Day style competition.
All competitors will be located in the same geographical area within 40 x 30 km where height differences are not greater than 40 meters. All competitor locations will be separated at least 500 m from each other.
Competitors are not allowed to substitute equipment in items marked with asterisk (*) by any other equipment unless permision is given by Judging committee.
Since this is a field day style operation each team will have a generator which has to be filled with gasoline. To avoid team members spending their time for re-filling generator we will have specially dedicated person at every location to help keeping it up and running during the contest period, so teams will concentrate on the contest battle.
Typical SWR vs. frequency curves for HF-37 tri-band antenna
Measured at the end of 50 Ohm coaxial feeding line
by use of AA-200 antenna analyser.
14 MHz band
21 MHz band
28 MHz band
Use of 80 m and 40 m Inverted Vee dipole antennas
1. 80 m Inverted Vee dipole antenna
The 80 m Vee feed point is at 37 feet, antenna is fed through 1:1 balun.
End insulators are at 5-7 feet above the ground level depending on a tension in guy wires. Insulators' positions will be pre-adjusted to get resonance at 3750 kHz while the rest of wire is rolled (see fig. 1). The rolls of wire are located at the lower end' insulator.
Unrolling this extra piece of wire along the guy rope will lower the resonance to 3525 kHz or to another frequency of your choice between 3525 and 3750 kHz. This "roll matching" is simple, once pruned needs no more adjustments. Walking to the field, unrolling the wire, fixing it with the tape to the guy rope takes less then 5 minutes.
The 1:1.5 SWR bandwidth is about 90 kHz.
Comments: The WRTC-2010 Organizing committee had tested different ways of broadbanding the Vees in a fact. The solution we chosen was found the most simple and repeatable in different circumstances. This classic solution was chosen in face of complexity of other designs and some field-style operation limitations. Of course, one can tune antenna length to the middle of 80 m band (e.g. to 3650 kHz) and make antenna more broadband using some technique (e.g. using known coax stub technique but you are allowed to do it at antenna connector only).
Fig. 1 - The roll of wire at lower end insulator serves for antenna tuning.
Fig. 2 - SWR of 80 m Inverted Vee dipole antenna when tuned to 3525 kHz.
Fig. 3 - Input impedance of antenna in fig. 2.
Fig. 4 - SWR of 80 m Inverted Vee dipole antenna when tuned to 3775 kHz (a bit too high in fact).
Fig. 5 – Input impedance of antenna in fig. 4.
2. 40 m Inverted Vee dipole antenna
The 40 m Vee feed point is at 33 feet, end insulators are at 9-10 feet, and it is easy (and will be done by volunteers) to prune it to SWR=1.15 at 7075 kHz.
The 1:1.5 SWR bandwidth is about 180 kHz.
You can readjust the antenna's resonance to the frequency you prefer in a few minutes.