Several people have asked for more information
regarding how I raise and operate 6m yagi antennas during
portable operation. This page is meant to be an interim
answer to address that procedure.
Full credit for the great videos documenting the way the portable
mast is raised and lowered during the DN34 grid DXpedition go to
K7SGP. We had discussed the possibility of producing some sort
of step by step video to show the parts in more detail, but we
simply did not have time. However, I have no doubt that the
information would help others in their efforts to activate rare
grids.
When I am on 6m EME DXpeditions, I use the larger 6M8GJ yagi and M2
Portable Mast, both of which come apart into 44" long telescoping
sections for easy transport as checked luggage on airplanes.
The methods used to erect that antenna are the same used on these
recent grid DXpeditions. There are some photos here on my
website that will answer some of your questions - the last section
of this page, entitled "MAST GUYING AND AND ANTENNA RAISING" is the
part relevant here:
You will notice that there are a couple of key points....
First, you need to tie the mast base to a ground anchor to it will
not kick out when you start raising it. The second trick is to
attach the "halyard" (the line that is used to raise the mast) to
some fastener so that it will hold the mast from rotating as you
pull it up. On my EME system, I use an eye bolt connecting the
last mast section together to provide this secure spot to pull
on. On the portable mast for these grid DXpeditions, I
simply used stainless steel hose clamps to hold a small right angle
shelf bracket to the mast so when I attach an S hook to it to pull
it up, the mast does not want to rotate. If the yagi is
attached perpendicular to the halyard attachment, the antenna will
just be smoothly raised and lowered at right angles to the ground,
without spinning around out of control and bending the elements.
The height of the Falling Derrick used depends on the amount of
leverage you need to raise the mast with the antenna on it. On
my EME setup, the 6M8GJ weighs around 50 pounds with the elevation
mount and boom truss assembly, and it is up about 20' to
21'. I use a three part telescoping Falling Derrick that
gives me about 10' of height. You will notice that I
made a simple base out of angle aluminum for it so it won't dig into
the ground (or sand) an can rotate as the mast is raised. Typically,
the base of the Falling Derrick is set near the base of the
mast. I put knots next to each other in the halyard so
the notch in the top of the Falling Derrick simply holds the rope by
virtue of it fitting into the slot. The knots dictate the
location of the Falling Derrick, and how much leverage you will have
in raising the mast.
In the video below by K7SGP, I also put black electrical tape around
the rope to hold it in the slot, so it would not fall out while I
was trying to get the Falling Derrick set up. I didn't have so much
leverage as I could have if the knots were slightly farther down on
the halyard, so the Falling Derrick was slightly more upright
at the beginning. However, by backing up a bit further and
applying more force, I was able to raise it easily. On
these grid DXpeditions, I used a lightweight aluminum mast (2"
telescoping down to 1.75") that was about 25' long, so the antenna
could be mounted at about 24.5' above the ground. I just
bolted together some lightweight pieces of aluminum tubing that I
was able to find at the junk yard. The Falling Derrick
used with it was made from screwing together three 5' sections of
threaded aluminum from the hardware store (sold as extensions reach
out and smooth concrete floors):
You can see that the mast is set on a "Prop" to provide clearance
for the yagi to be bolted to the mast before the it is
raised. The prop is simply adjusted by slipping a piece
of aluminum tubing inside another, and holding it at the proper
heigh with a hose clamp to prevent it from collapsing.
The Prop is held upright by three small guy lines held in
place with tent pegs. Since the only force on the Prop
is straight down, the only important thing is that the top of the
prop (with the part shaped to accept the mast) be held firmly in
position. By holding the Prop in position, it will be ready to catch
the mast when the antenna is lowered again:
Here is how the larger antenna was raised last summer in
KH8. Now you can see why I taped the Falling Derrick
between the knots on the halyard during the recent grid DXpeditions:
You can see how it might be necessary to have some help lowering the
antenna if the prop has moved slightly during operation. In
this I tripped a number of times over the guy lines for the Prop
during the middle of the night when I was out aiming the antenna, so
the prop was slightly out of line. You can also see why
I taped the halyard to the Falling Derrick during the recent grid
DXpeditions
When possible, it helps to be able to set up the antenna so you
raise it with the wind and lower it into the wind. It also
helps if you have another person to "walk the mast" up or down as
you raise or lower the antenna (although one person can do it
alone). Here is a film clip of lowering the 6M8GJ at the end
of the 6m EME DXpedition to Fiji:
The key to success in this whole operation is to make sure that the
SIDE MAST GUYS stay tight during the entire raising and lowering
process. If you have a flat site, this is easy - the guys just
have to be anchored out away from the base of the mast the same
height that they are attached to the mast. Of course, when you
attach the guy lines to a bearing plate, as I do, the actual height
on the mast is calculated as to where the guy lines would extend to
the center of the mast. If the height of the attachment
(H) is equal to the distance out to the guy anchor (also H), the guy
length is then:
L = Square Root (2H^2
) = 1.414 H
In practice, it is good to have the guy lines be a bit longer than
the above calculation, since the exact location of the guy anchors
may have to be adjusted for the slope of the ground. If the
ground is uneven, you may have to do some adjusting of the length
and position of the side guys before the antenna is mounted, to make
sure that the mast can be raised smoothly with the side guys
remaining tight. That way, the antenna can be raised without
getting out of control, and when it is lowered, it will be guided
directly back down onto the prop again. So, the first
step is actually to practice raising the mast by itself to make sure
you have the side guy lines properly set:
The front and rear guy lines can be whatever lengths are required to
provide good stability and also hold the mast vertical.
To aim the antenna, use an AIMING
CIRCLE mounted so the mast just fits through it.
The antenna is held at the desired azimuth by using small diameter
nylon lines tied to the boom. The lines are then secured
to trees, or guy anchors and adjusted in length until the antenna is
aimed in the proper direction. Care must be taken not to put
excessive downward tension on the antenna, or you will bend the boom
or cause it to point upward or something...the goal is to prevent it
from moving side to side, so the further out away from the antenna
and the higher you can tie off the lines, the better!
I hope this helps answer the basic questions of how I do it on my
portable operations, and is of use to others in setting up for
portable operations. Let's do more 6m DXpeditions!!!