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Mike Dennison <mike.dennison@ntlworld.com> wrote:

>Although it is interesting to know the ground conductivity, the main
>losses in a small LF antenna are environmental. This includes losses
>in trees, buildings etc. These are sometimes all lumped together and
>misleadingly described as 'ground losses'.

Hi All,

I've been making some changes/measurements on my rectangular loop

which seem to confirm Mike's findings. The loop is 3.5m high by 8m wide.

It has a DC resistance of 0.5 ohms and an RF resistance (at 136 kHz

resonance) of 0.9 ohms (skin effect?). I recently put two 550 microHenry coils in the

horizontal parts of the loop - each coil has a DC resistance of 1.5 ohms and

a Q at 136 kHz of about 120 ie an equivalent series resistance of about 4 ohms.

I was hoping that the total equivalent series resistance would be about 10 ohms

(ie one loop plus two coils) but it measures 40 ohms !!

The loop is hung from the branches of trees and although not totally

surrounded by leaves, it's more than 50%. As there is no earth connection

involved I guess the extra 30 ohms of loss is due to the dielectric properties of

the wood and leaves.

Brian - G3YKB

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