My neighbors throw away
some great stuff!
This time, it's a perfectly good
beach umbrella "skeleton" (no fabric).
All the mechanical parts work,
the wood is in good shape.
And perhaps best of all,
each of the eight umbrella ribs
is a quarter wave at 6 meters!
The umbrella skeleton is made of
mahogany. The finial cap is plastic.
Here's my experiments to make it
resonate on 50 MHz.
... has to mount on the top of the
plastic finial somehow
The finial looks like terra cotta clay
but it's actually some pretty dense
plastic material that simply unscrews
from the rest of the umbrella.
But the mounting bolt doesn't pass
all the way through the finial.
It doesn't need to, of course,
when it's life is that of a beach umbrella.
For use as an antenna, here's how I
fed the coax up, through the plastic cap,
PLUS allowed mounting/dismounting of
the driven element.
I hope the pictures show
what's happening here.
RG-58 coax comes up through the
lower piece of clay colored plastic
through a hole drilled OFF CENTER.
The normal mounting bolt occupies
the center space in the two pieces
that make up the top of the umbrella.
The coax ends in ring lugs.
Another off center hole, this time
in the top or finial, allows a 12 ga
solid copper wire to pass the signal
out through the very top of the assembly,
where it too ends in a ring lug.
The very top center of the finial
is normally empty. There is no hole
or bolt in the thing when it's a
bumbershoot. I drilled a hole
just slightly SMALLER diameter
than 3/8 inch, then THREADED a
standard 3/8-24 antenna stud/bolt
into the hole. The plastic is very
dense and threads nicely.
I can mount either a stud and 3/8
threaded sleeve, or a 3/8 hex head
bolt into the threaded hole, and
attach just about any kind of
commercial or homebrew whip to that.
The pictures show a simple piece of
6 ga solid copper wire, 54 inches long.
In one of the photos, you can see a
choke of about 8 turns of the RG-58
around the top of the wooden mast.
Chokes aren't terribly necessary for
my operations, I'm always 5 watts QRP.
At those power levels, there's
not much to choke off. But I needed
to store a bit of the excess coax,
so "neatly wound coax reserve" or
"RF choke" - you decide.
Radials are next. You can see
part of that happening in these
Counter That Poise!
You know you're a ham when you
look at objects and estimate their
size in WAVELENGTHS instead of
feet or inches or centimeters.
When I saw this neglected
umbrella skeleton sitting on the
bulk trash pile, I saw eight "spokes"
each a quarter wave long at 6m.
Sure enough, they are each exactly
54 inches long!
I cut eight pieces of tinned, copper
quarter inch braid, each to 54 inches
plus an added six inches so I could
attach and trim later.
At the distal end of each piece of
braid, I mounted a 1/4-20 bolt and nut.
I wanted the ends adjustable. Shrink wrap
and the "Chinese finger cuff" effect
of the braid holds the nut captive.
I can unscrew and remove/replace
the bolt if needed and the nut
stays in place and aligned.
I marked all the radials at
19 1/2 inches so that if I
decided to use it for 2m,
I could figure out a way to
plug and unplug the xtra
section of radial wire.
I'm also toying with the idea of building a
discone. In that case I think(?) I'll need to
add a few inches to the radials. If that's
the case, I'll unscrew the bolts and insert
lengths of allthread rod.
Tune it Up!
The height adjustment method, for the
umbrella, is the typical series of holes
with a peg-hook thingie inserted in the
I stuck the peg in each hole, set the
umbrella canopy (now the groundplane radials)
on each peg and took measurements.
When the umbrella (the radials) are pegged
at the typical 45 degree angle (down a bit
from horizontal) the resonant freq is LOWER.
As I raise the radials toward horizontal,
the antenna is resonant at a HIGHER frequency.
I marked all the holes as to their best
frequency, based on SWR and reactance.
I drilled two additional holes to allow
setting the radials at the lower, 45 degree angle.
Tunes up at under 1.5:1 across the entire band.
Rapid Deploy Station
Urban Desert Ops
EMT Conduit Antenna
Recycled 2m Yagi
Mil Mobile Base
6m Ground Plane
Return to QTH
The rest of my life?