On 5/21/2013 8:40 AM, Bob K6UJ wrote:
Sometimes my local power line noise is about S8 or so on 160.
I am considering the purchase of one of these magnetic loop antennas
for receiving to see if it helps.
Anyone have one of these ? How well does it perform ? One better
than the other ?
Pixel Technologies RF PRO-1B
Wellbrooke Communications ALA 1530
Bob
K6UJ
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.
If you are primarily interested in 80/160 meters, then you
might want to look at my NCJ article:
http://www.n6rk.com/loopantennas/NCJ_loop_antenna_N6RK.pdf
This loop is normally 20 feet in circumference and can
be made up 40 feet in circumference to get additional
signal. Also, it is tuned, which produces much more signal.
I use it with no preamplifier (besides the one built into
the radio), although a little gain wouldn't hurt.
Due to popular demand, I will be offering assembled
versions of this loop for people who are not able to
build the homebrew version described in NCJ.
Rick N6RK
All good topband ops know how to put up a beverage at night.
_________________
Topband Reflector