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From: Anselmo HB9ICK-IZ3BGJ
Date: 4/15/99
Time: 8:21:28 AM
Remote Name: 208.21.129.91
Dear friends, Today it's snowing in Geneva and cannot carry tests outside but I have some interesting observation to share. I measured resonance and impedence without any coil at frequencies around 70 MHz on the subject patent antenna.
Its dimensions are: dish of 34 cm dia, cylinder 10 cm high, 10 cm dia, 15 cm above the dish, copper connecting rod of 12 mm dia.
The impedence behaviour is very similar to the Stefano's CFA where the dish (the ground plane for Stefano) is not a fix ground reference but is part of the radiating system. In fact, using the MFJ259B and looking for X=0, the resistance varies from 10 to 90 ohm depending on the connection shape between the dish and the instrument ground: using a 50 ohm coax the impedence is stable at 8-12 ohm but using two wide spaced short wires the impedence can be raised to 50 ohm. In such configuration and connecting a simple wire of 1 meter to the ground of the MFJ259B, the impedence can be moved up to 90 ohm depending upon where the 1 meter wire goes.
This means that in any CFA configuration the "ground" reference is of capital importance in obtaining reproduceable measurements and tests. By sure the E field shape depends largely on how it closes to ground. Being an electrical field is much more subject to shape change due to form of sorrounding conductors and E field shape dictates the efficiency of the CFA.
So my suggestion to all those who want to experiment with the CFA is to use a very rigid and stable ground plane which dimensions will largely influence the antenna behaviour.
More tests are necessary to assess the relationship between the "ground" reference and overall characteristics.
This is all for the moment, good luck. Anselmo HB9ICK-IZ3BGJ