Hi Mike
Whilst the mast was down I modified the capacity hat. There are three 17m
long parallel wires, about 0.5 metres apart (total span 1m). The wires are
joined at both ends. (See http://www.lf.thersgb.net/antenna.htm for a
picture).
I changed this so that the wires were only joined at the far end. Now the
vertical wire and the elevated coil are connected to the centre wire only.
The RF travels along this centre wire to the end, then back using the
outer
two wires in parallel..
I expected this to increase the inductance of the antenna and so lower its
resonant frequency. The actual effect was the opposite - the frequency
increased and I had to add inductance at the base of the vertical.
I can't offer an explanation but modelled the two antenna configurations on
EZNEC3.
Making some assumptions regarding ground and the two coils the original
configuration resonated at 336.7kHz. The new one resonated at 138kHz. There
was also a 0.15dB loss with the latest configuration.
Regards,
Peter, G3LDO
e-mail <[email protected]>
Web <http://web.ukonline.co.uk/g3ldo>
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