6 x 6 Loop Antenna

Posted on Feb 7, 2014

This new loop antenna by Graham Maynard is his best design yet and I am proud to be the first to present his work. It uses one, six foot square, six turn loop, and is aperiodic in nature, covering the frequency range 50KHz - 5000KHz. The loop is of a size that can be mounted inconspicuously against a garden fence away from household interferences.

6 x 6 Loop Antenna
Click here to download the full size of the above Circuit.

This new `6x6` design uses the centre tapped loop winding as an input phase splitter. This ensures low distortion push-pull operation. The amplifier also has a low impedance shunt input which maximises gain. These aspects give it a better signal to noise ratio than with a single ended or high impedance amplifier. The amplifier provides a useful gain of 42 - 54dB over its frequency range, see the Bode Plot below. Please note, that the Bode plot is derived for the amplifier circuit ONLY, it is not possible to simulate the characteristics of a six foot square loop. The first MPSA18 transistor on each loop operates in common emitter, the collector being directly coupled to a double emitter follower pair. The circuit has self DC biasing, the emitter of the first BC550C being coupled to the base of the MPSA18 transistor. The network of resistors and capacitors around the base of each MPSA18 transistor tailors the amplifier response to the specified limits. The double emitter follower pair evenly distributes the Class A heat dissipation, and direct feedback in the bias chain, counters temperature drift effects. The output from each amplifier half is fed via a 2:1 tri-filar wound push-pull output transformer, with the output winding sandwiched between each primary half. There is equal but opposite current flow and therefore maximum linearity. The output is isolated, which minimizes earth loop noise injection, either via receiver...

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