You also get the added benefit of pre-selection because your loop will only be amplifying the specific frequency you are tuned to. A tuned loop is designed according to a formula such that if there are the right number of wire turns of the correct shape and size, a variable capacitor connected to it will bring the loop into resonance throughout the AM band providing much more signal than if it were the same size but not tuned.
Tuned loops such as this Tecsun AN-100 on the other hand can provide extremely high gain without any electronic amplification in a small size. Loop At Lower Left Can Be Rotated By A Front Panel Control However, smaller untuned loops of the type that come with most of today’s typical table top radios or A/V receivers generally provide lackluster reception and are primarily a cheaper alternative to the superior ferrite rod… these loops work after a fashion as long as signals are strong enough. Such loops can span entire bands or groups of bands effectively…the T2FD loop is one good example of an untuned loop. Untuned loops can be very effective if they are large enough to capture enough signal. The main advantage of an untuned design is that it doesn’t have to be re-adjusted for each frequency you tune your radio to. Ferrite rods and loops are also directional which allows them to be aimed to maximize reception or minimize interference. By comparison, wire or whip antennas tend to pickup more noise.
This is a prime benefit of all loops including the ferrite rods inside almost all portable AM radios which are, after all, simply loops made more efficient by their ferrite core. Loops respond to the magnetic portion of the RF signal and ignore the electrical component where most of the noise is. In common with both types is the ability to reduce RFI – Radio Frequency Interference. Tuned vs Untuned: Loops can be designed either way and each has strengths and weaknesses.
When smaller table radios appeared in the 50’s and 60’s they contained a loop of wire, usually wound on their back panel. Some loops were ornate and sat atop the radio, others, like the Zenith boxed loops pictured further down on this page, were mounted inside the console cabinet and could be “aimed” – rotated by a front panel knob for best reception. Long before highly efficient ferrite rod antennas were commonplace, early radios required either an outdoor wire antenna (called aerials in those days) or a loop antenna.
Overview: Passive loop antennas are not a new invention – they’ve been around as long as radio has been. aesthetically pleasing and nicely designed and of good mechanical quality. These Tecsun antennas are beautiful antennas…some might call them artful…. The Tecsun AN-100 is also sold in other areas as the model AN-200 which appears identical in every respect except for the style of the plastic base…they can be found under the names Grundig and Kaito as well as Tecsun. If you haven’t tried one out you’re in for a treat! The good folks at Tecsun Australia just sent me their Tecsun AN-100 to check out and as usual I pitted it against the well-known Terk AM Advantage AM antenna and a few others I have on-hand, such as the excellent but no longer available Select-A-Tenna. It has been a while since I last reported on passive AM loop antennas…the smallish variety that are such a cost-effective way to perk up your AM radio reception on the cheap.