Antenna construction

[Ron T]

I have built a pair of loop antenna, roughly 0,75 metres in diameter. While winding I lost count of the number of turns, somewhere around 27 turns of twisted pair, but both loops used almost identical lengths of wire. After constructing them I did some measurements of inductance, impedance (@1KHz), DC resistance, and self resonance. The two loops are matched better than 1%, except self resonance where they're within 3% of each other (centering around 83.5KHz). Now I'm wondering if I'll be able to pick up anything as I won't be able to mount them away from the house.

Next step, build the pre-amps.

Ron VE8RT

[Thomas_LR]

Hello Ron,

83.5 Khz ??
The value is too high, she must lie to 10KHz, increase the value of the capacitor in parallel with the coils.
What is the capacitance that you used ?

Thomas

[Ron T]

That was the self resonance frequency of the coil, without any capacitors across it. In retrospect I should have calculated the coil Q too, but I don't have them at work now, where the test equipment is.

[Thomas_LR]

The self resonance of the two loops are the same ?

[Ron T]

I'm having trouble logging in or staying logged in. But I'll try a second time to reply.

An effort was made to match the two loops as closely as possible. The self resonance of the two loops was just outside 1KHz of each other. The loops were wound with twisted pair wire with two wire ends tied to each other to form a single center tapped winding. I had in mind to ground the center tap and connect the loose wire ends to the inverting and non-inverting inputs of an op-amp in a differential amplifier type. The thinking was that the loops would be relatively low impedance and would better match the lower impedance of a differential single op-amp design.