by Attilio I1BAY – I QRP Club 309


This antenna matches the needs to reduce as much as possible dimensions and weight trying to maintain a high efficiency across all bands.
I believe the sketch is self explanatory.
The antenna has been several times used during SOTA activations with positive electrical results, little bit less as portable due to his dimension and for the difficulty to find two points to hang it on the top of the mountains.
However it remains a good solution for a fix operation or for a field day as, in the last case, it can operate at a lower altitude where we can find trees and, not being obliged to carry the whole equipment on the shoulders, we can use some poles.
I need to write some more words to explain traps construction.
The balun is 1/1: toroidal core for HF, colour light viola; size: external diameter 37 mm., thick 17 mm. (able to handle hundred W ; compact coax with well insulated center conductor stranded (or a small size coaxial cable 52 Ohm ).
Starting from the center of the antenna, wind the cable well tied on a half part of the toroidal core with 9 turns, go back to the begin (crossing the internal part of the toroidal core ) in a diagonal way and wind further 9 turns in the opposite direction to the first nine, to reach than the SO239 connector.
Let see now how to build a trap… the wire which is coming from the centre of the antenna has to be soldered to the shield at the beginning of the coax winding the trap, the “hot” wire (center) of the rolling has to be soldered on the shield on the out part of the rolling of the trap, the “hot” wire (center) has to be soldered on the cable going on towards further traps.
All to be placed on a Plexiglas insulator, than fix using an insulant glue.
Number of turns for each traps and diameter according to the sketch.
Max power rated is depending from the toroidal core and from the size of trap coax, the one described can support more than 100 W.
I suggest to use high quality coax for traps.
Last year I have used this antenna, and few Watt, during SOTA activations making hundred of QSOs worldwide, enjoy your self!

Please find here below the drawing: Filare 

Italian version