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Old October 28th 05, 08:23 PM
Reg Edwards
 
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Default HIGH Q CAPS FOR VLF LOOP ANTENNA?

Trabem,

Without wishing to detract you in any way from your objective of a
matched series tuned loop I would like to describe how I would do a
similar job with the usual parallel tuned, multiturn loop.

I do not understand the type of receiver you propose and I am not
seriously interested. But I should say the theoretical working
bandwidth of my proposal is about 1/2 of yours.

Actual bandwidth of both your and my proposals is indeterminate
because of the uncertainty of ground proximity and nearby
environmental loss. The working bandwidths could be very similar.

Using similar size loop dimensions to yours, ie., 5.3 metres square -
Frequency = 60 Khz.
5 turns of close wound 2mm diameter enamelled wire.
Inductance = 710 micro-henrys.
Tuning capacitor = 0.01 uF approx.
Reactance of L and C = 268 ohms.
Conductor resistance loss = 2.5 ohms.
Intrinsic coil Q = 107
Matched working Q =53
3dB working bandwidth = 1.12 KHz.

Impedance match to 50-ohm receiver obtained via small coupling loop,
in the same plane, about 1 metre square. Working Q = 53 or less
depending on height above ground.

The working Q may not be high enough for your particular application.
I describe the antenna for you to see what is possible in comparison
with your series-tuned proposals.
----
Reg, G4FGQ.


 
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