Richard Karlquist wrote on May 21.
It is important to understand that these loops have
a circumference of 10 feet, which they are limited
to because the manufacturers want to offer a bandwidth
up to 30 MHz. Also, they are untuned, again because
the manufacturers want to offer a broadband solution.
Very little signal is available from such a small untuned
antenna, and hence these antennas require a high gain
preamp. Depending on your location, the amplifier
noise may be the limiting factor on sensitivity.
One of the commercial loops claims to have 0.5 dB noise
figure, however I measured 3 dB on a sample of one.
These issues are simply physics, no matter who builds
the loop. IMHO, a so called "Moebius" configuration
doesn't fundamentally change anything with respect
to these tradeoffs. As the inventor of that design
states, it is only an advantage for its intended purpose
of EMP weapons testing.
Rick,
The most important limiting factor in regard to sensitivity with a small
wideband loop is the loop/amplifier mis-match over several octaves. Any
mis-match is equivalent to putting an attenuator in front of the amplifier.
Hence, the amplifier noise figure is not a significant factor.
That is why Wellbrook use an amplifier that copies the loop element
reactance over at least 5 octaves.
Where the small loop size is a limiting factor for Topband and MW Dxing,
then the large Aperture ALA100 offers significantly better performance, when
used either as a single or Phase array antenna.
73
Andrew Ikin G8LUG
All good topband ops know how to put up a beverage at night.
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Topband Reflector
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