Antenna : TRAP-dipole untuk 20m dan 40m band
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Sumber: http://www.qsl.net/on7eq/projects/holidayant.htm
A simple TRAP-dipole for 20 and 40m bands
- Performance on 20m is moderate, this is due to low elevation of antenna. By experience, I have noticed that a 20m band dipole antenna must be elevated by at least 8m above ground to perform well ! There are at least to 2 or 3 S-points difference between a 20m dipole elevated at 3m and 8m ! See the EZNEC simulations below.
- Performance on 40m is very good. A 40m dipole at this height becomes omni directional, so do not worry about the orientation of the dipole vs. 'homebase'. You will be amazed by the results obtained, both for continental contacts and real DX ! I worked several ZL with this antenna only 3m high in SSB with 100w ...
- A dipole has a nominal impedance of 73 Ohm, but at this height this will drop to 50 Ohm. No problems to operate over the full 20 and 40m with SWR < 1.5, so you will not need a tuner, if you adjust the antenna well.
- Construction of traps : see my page on the site
- A balun is not a 'must' but recommended ...
- How to adjust the antenna ? Cut all wires + 20 cm too long and assemble the antenna, completely with traps. First adjust the 20m section, cut both ends carefully till resonance on centre of band. Then adjust the 40m section by cutting tail ends till best SWR at band centre.
- Dipole wire lengths : I made several different dipoles and observed for 20m section 5m07 to 5m10, for 40m section 3m40 to 3m38, but total is 8m47. Length can vary according to elevation, ground conductivity, presence of surrounding objects (trees, house, ...)
- If the dipole is mounted as inverted-V with apex height @ 6m on a fiberglass pole, I observed lengths of 20m section of 5m20 and for 40m 3m25 (total = again about 8m45, wire section 4mm²) I used this antenna in the IOTA contest in 2007 activating EU-105 with good results ( see picture ).
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