I live within long walking distance of the Homebush Bay, Sydney medium wave transmitter site. The signal strengths are high. With wideband antenna systems, the radio exhibits desensitization. A tuned loop antenna effectively acts as a tuned circuit or RF pre-selector. The higher the circuit 'Q factor', the narrower the 3 dB bandwidth when the variable capacitor is tuned to resonance.
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It is easy to desense my radio by aiming the loop towards the local MW TX antenna site. Imagine how higher the desense would be if a wideband antenna was aimed at the local TX antenna site.
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I built a Gary DeBock design 9-turn 40 inch (100 cm) side length PVC box loop. The tuning capacitor is standard 360 pf. The tank coil wire diameter is similar to what Gary recommends in the article PDF (link below). The loop works well at my suburban house location. The loop would work even better at a rural location, or coastal site overlooking the sea. Adding an RF amplifier is not necessary, partly because the total composite QRN and QRM at 525-1710 KHz is high. I use a Sangean PR-D3 radio which is largely modelled on a Crane CC 2E. The RF noise figure of the internal DSP chip is usually RF noise-limited at MW.?
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I also use a smaller 26 inch (65 cm) diameter PVC 'hula-hoop' tunable C-LOOP-HDXXLTAM HD series loop manufactured by PK Antennas, Melbourne. The SNR on the smaller loop is similar to the larger 40 inch diameter loop. This means that the loop antenna overall diameter can be small enough to fit on a standard kitchen benchtop. This is where I do most long distance MW listening. When especially interesting signals appear, the 40 inch diameter loop is used.?
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Thanks,
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Todd.
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