Traps for 40/80 m dipole

An alternative to traps made with coaxial cable, criticized for ineffectiveness by some authors (1), is a thing from the past: a classical realization of a resonant circuit with lumped elements. Two resonant circuits, easy to reproduce and suitably robust, were made. A pipe resin, commonly used as a garden lighting support, is used to hold the inductor. The external diameter is of 60 mm and is 130 mm long. On this sleeve, 6 holes for mounting the inductor and capacitor were made.

Using as a conductor of the inductor a unipolar power cable in PVC (N07V-K) 4 mm2, come in exactly 14 turns. Observe the photos submitted to see how to secure the cable. The condenser is realized using a both-sided copper vetronite board,size 100 mm x 55 mm. It's necessary to create the plates as shown in the pictures so to have an area common to both plates of 50 mm x 50 mm. This will get us a capacity of about 62 pF. To realize the plates, the copper to been kept was masked with a simple wrapping tape -50 mm wide- and then the board was dipped in acid to remove the unprotected copper. In this way you get more than 6 mm of insulation at the edges of the board. The capacitor is fixed to the inductor with two 25 mm long hexagonal columns. The tuning is made by subsequent attempts, removing a little bit of copper from the plates, for example using a cutter or an end mill. Once completed the calibration, the capacitor is protected with a generous spray of paint. After welded wire terminals, also connections and welds should be protected with paint . As in this case when you work with glass fiber material it's better to use a mask and possibly a pair of gloves. Here's to good transmissions!

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Documenti: Disegno Trappola PDF

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(1) W8JI - http://www.w8ji.com/traps.htm