On
the left mounted vertically a MFJ-1788 for 40-15M,
centre
is my ground mounted home built magnetic loop for 80-40M
and on
the right mounted horizontally is an MFJ-1786 covering
30-10M
and is an excellent DX antenna.
Click
on image for a larger view.
This photo is of my home built
magnetic loop.
I
have just recently added a variable vacuum capacitor which now allows me to
tune it across the 80 60 & 40M bands and constructed a remote tuning
facility.
<
Click on the photo for more information and photos taken during construction.
I use a MFJ1788 40-15M magnetic loop and I am extremely
impressed with the performance especially on 40M where I thought due to the
small size it would not be so efficient but it compares favourably with my
ZS6BKW dipole at 12M AGL but most importantly the noise levels are way down, up
to 6 S points less on the loop.
Then
I acquired a MFJ-1786 30-10M magnetic loop which I have mounted horizontally. The
1786 is turning out to be an excellent DX antenna even though it is only 1M in
diameter and only mounted at 3.5M AGL.
My
experience with the MFJ loops is that they work well. The loop is welded to the
air spaced capacitor and then each plate in the capacitor is welded again to
each other. Also the facility of powering the tuning motor via the coax feed
makes for a very easy and simple installation. If they are loft mounted or
mounted horizontally, as with my 1786, then a slight adjustment of the shape of
the feed loop will bring the SWR down below 1.5.
As
you can see from the photo , I have my 1786 loop mounted horizontally and the
other one is mounted vertically on a 3M telescopic tripod. MFJ say in their
user manual that for best results mount at least 20ft above any ground plain
when using horizontal. I discovered by
accident that it is a very good DX antenna even though I only have it mounted
at approximately 12ft AGL.
I
compared the performance of the two polarisations and discovered during a short
test there is definitely a big difference between vertical &
horizontal and strangely enough not in the way I would have thought. Listening
to the beacons on 17M (please keep 18.110 +/- 3kHz clear, thank you) beacons
that I could hear on the vertical loop were between 4 & 6 S points stronger
on the horizontal loop, and off course the noise level is even lower. I even
extended the tripod to full height, which would make the bottom of the vertical
loop approx 3M AGL, but it made no difference at all in signal strength
when receiving the beacons on 17M so height is not important when
vertical.
< click on each image to enlarge
Over
the last few years I’ve tried various wire antenna configurations, loaded
dipoles, full sized resonant dipoles, G5RV designs and vertical antennas with
many radials laid out but the noise levels make verticals almost useless and
mounted at ground level they just don’t receive DX signals very well. The best multi band wire antenna so far is
my ZS6BKW design which is mounted in the clear at 12M AGL and works well on 40
& 80M, but I consider that the MFJ-1786 & the 1788 loops out performs
it on 40-10M both for short range & DX work mainly because I can now hear
weak signals, and if I can hear them I can usually work them. My home built
loop for 80 60 & 40M works just as good as the ZS6BKW dipole, signals are
sometimes one or two S points down, but noise levels are down between 4 – 6 S
points so again weak signals become workable.
So
if you have a small plot/garden, or no garden at all, it is worth considering a
building or buying a magnetic loop, I guess in the near future that I will be
removing all my wire antennas.
73’s
de Mike G1ZRN.
>
My Loop