MAGNETIC LOOP   

You can easily Install this antenna the day
that it arrives and be listening to all
frequencies between 100 kHz and 30 MHz
within a couple of hours!

Here is what the manufacturer says about
the antenna:

"The antenna is designed to receive the
magnetic field of a transmitted electro-
magnetic signal and reject the electric field
which the opposite of normal antenna that
are optimized to receive electric fields.

Because it is designed to reject near- field
electric fields it is quite effective at rejecting
man-made electrical interference from such
sources as power lines, light dimmers, arc
lamps , fluorescent lights, switching power
supplies, computers and plasma TV’s
which produce large electrical fields.

To low angle of arrival signal (like ground
waves) it has a figure eight reception
pattern with very sharp nulls located at
right angles to the plane of the loop. These
nulls can be used to gain an additional
25- 30 db of signal rejection to local
undesired signals if the loop is rotated on
its vertical axis to orient the undesired
signal within the null.

To high angle of arrival sky-wave signals
like what is received off the ionosphere at
night, the reception pattern is almost Omni-
directional."

Because of the small 38 inch diameter and
light weight of this loop, the antenna has
been initially mounted on a carpenters saw
horse and rotated using a light duty TV type
rotor. This allows very easy relocation to
different spots on the property for testing.



























The antenna rotor that is used is a Channel
Master CM9521A TV style unit. It was
selected because it was the only rotor that I
could find locally on the day that the antenna
was installed. Internet reviews say that it
should be taken apart and the gears
lubricated before it is used. It is also
suggested that the shaft seal be greased so
that rainwater does not get into the unit.  
W6SDO.COM                                                   SAN DIEGO, CALIFORNIA USA     
The antenna's small capture area is
compensated for by a built in preamplifier
that is included by the manufacturer with the
antenna as it is delivered.

In order to help choose the optimum antenna
mounting location, a loop belonging to a
nearby ham (Bruce, WA6DNT) was used so
that A-B tests could be preformed by
deploying each of the antennas at a different
location. One antenna was operated at
ground level behind the house and the
second antenna was located on the deck
above my garage in front of the house.

Because this loop responds mostly to
vertically polarized signals, the height above
ground should not be critical.

We soon learned that at the ground level
location the antenna seemed much more
susceptible to all sorts of terrestrial noise
as well as the birdies that came from the
surrounding households (plasma screen
TVs being the worst offenders!). This was
true even when we moved the antenna
around in the back yard. The test was
conducted during the day and our own TVs
were turned off. The noise level at the higher
of the two locations was often (but not
always) one to two S-units lower than the
location near the ground. Since one of the
antennas was at the rear of the house and
the other was at the front of the house, we
may have to try another test to see if this
accounted for part of the difference. More
testing of this loop antenna at alternate
locations and heights is planned for some
later date.

This loop has a sharp null for low angle
incoming noise signals. It has been found to
be very effectively on all of the ham bands
in eliminating the noise, or another radio
station, that comes from any single
direction.

The loop It is particularly effective on 160
meters where, in the presence of my high
urban noise level, I can dig a signal out of
the noise using the loop where all other
types of antennas fail.

With these first two antenna systems, the
vertical dipole and the loop, I had excellent
all band listening capability during the
period that I was studying to get my license.

The following is a good example of how
well this antenna performs. During the
2012 DX SSB contest on 160 meters I
worked the band from 5 pm to 9 pm on
Friday February 24th only. During this
period I made 44 contacts in 15 states
plus Canada and Mexico. Most contacts
were completed using my quarter wave
inverted L. However, nine of the contacts
(20 %) were easier copy when listening on
the loop (located on the deck over the
garage). Four contacts could
only be
copied on the loop (9%) because of the
high S9 to +10 noise level on the inverted L
antenna. No contacts were better on the
loop that is located at ground level.

Like they say in the weight loss ads – the
results that you get may vary. However,
I think that I’ll keep the loop!







      Last revision December 9, 2012