Measurement tables for the Extended Top-load Spiral Aerials

The following measurement tables are for the extended top load aerials with the double spiral. This consists of a spiral inductor wound from the centre out to the ends on the underside of the bamboo cross supports and then continued, in the same winding sense, back into the centre but cleated to the top of the cross arms. The measured inductance of the double spiral was 709 uH. The first table is for a double spiral with the conical capacity hat. The increased inductance of the double spiral decreases the natural resonance to 447.3kHz.

The next configuration has the double spiral, with the 16 wires forming a conical capacity 'hat', then a 28 metre wire was attached to the pinnacle and led away at the same height for 14m and then sloped towards the ground. (Model A on the diagrams). The natural resonant frequency was 342.7kHz

In the next configuration the top wire was connected so there were two 14m wires connected either side to the apex of the conical capacity hat.(Model B). The natural resonant frequency was measured at 349kHz

A further two wires 14m were connected to the apex or the conical capacity 'hat' to give a total of four, they are not at right angles due to the available space and supports. This is shown as Model C, and its natural resonant frequency of 311kHz.

For Model D the ends of two of the pairs of top wires were connected togther to form a 'bowtie' wire load. The extra capacitance brought the natural resonance down to 266 kHz. The reason we were able to start measurement now at 87kHz was that, between the last two measurements, Finbar carried out some 'surgical operations' on his bridge drive oscillator.

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