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6 Spoke BCB Loop Antenna
Hexagon Loop Antenna
Here is a little twist on my loop designs. This is a 6 sided loop
antenna. From what I can tell, there isn't any difference between a square and a hex
loop besides the shape. I like to build things that look nice around my house (or
someone else's house). I had help with this project. My friend Fred Wise from Glen
Burnie, MD was kind enough to make the round center portion of this loop for me.
The block of wood is 5-1/4 inches (13.4 cm) in diameter and has six 1/2 inch holes
expertly drilled an
inch deep. The 5 spokes are 12 inch (30 cm) long, 1/2 inch (12 mm) hardwood dowel rods.
The 12 inches allowed
me to use an entire 4 foot long dowel. The mast dowel is 22 inches (56 cm) long. A little shorter
is fine also. I used what was left from a dowel I had.
I didn't want to thread wire through lots of holes on this loop. That is a summer outside
project. I decided to use some 5/8 inch (1.6 cm) long brass escutcheon pins The diameter of the
pin is about 1/16 inch. 98 pins are required. 16 on each of the 5 arms and 18 (one
for the end of each coil extra). I used a V block (also made by Fred) attached in my
drill press to drill the pilot holes with a 1/16 inch drill bit. I set the depth gauge
for half way through the wood.
Before I drilled, I stained and finished the dowels. I then took 6 strips
of 3/4 inch wide masking tape and carefully stuck them to a piece of plastic. The measurements
were made with an adjustable square. I marked in 1/4 inch (6 mm) for the first hole. I then marked
17 more holes on each piece of tape, in 3/8 inch increments. The mast will have all
18 holes while each arm will be missing the second hole from the outside. This allows
for extra spacing of the pick up loop. I then marked a line down the center of each
piece of masking tape. The picture shows 7 tapes as one was used for a test run.
The masking tape is then moved to each arm. This provides the drilling
location for all the holes. One idea is to elevate the V groove block slightly
to when the pins are nailed, they will angle slightly away from the center. This
would keep the wire against the dowels. That will happen on my next loop.
After the holes are drilled, the pins can be nailed in, leaving a 1/4 inch
or a little less showing. Then the spokes can be glued or otherwise fastened in the
block. The dowels can't be allowed to turn or all the wires might fall off the
pins. That would be quite a mess!
The wires are now ready to be wound around the pins. About 90 feet
of wire will be required for the 16 turns. 100 feet (30 m) will give you a better safety
factor, just in case I goofed up the math.
I started with the
single outside turn. That takes two pins on the mast spoke and one pin on each of
the others. Leave enough wire length to go to two binding post connectors. The
other winding is wound with 15 turns, beginning and ending at the mast spoke.
(See why the extra two pins were needed in that spoke?)
The ends should be wound several times around the pin to hold the wire in place.
On the 15 turn winding, I wound an extra turn around each pin on the mast spoke
to further aid in holding the wires on the loop. Pulling the winding tight and
pushing all the wires towards the dowel after
each turn is recommended. This step is pretty easy. Check your work every couple
of turns to make sure you didn't jump a pin.
A 365 pf variable capacitor is connected across the 15 turn winding,
while the single turn winding ends were terminated at some binding post type
terminals using knurled nuts to fasten the wires going to the radio. A good support
base should be made to keep the loop standing upright. Care should be taken to keep
the loop from falling over as this could damage the mast.
The loop works pretty well and much as expected. There is one major
difference I found between the "harpo" and the spiral wound loops. The harpo will
tune 540 to 1700 where this loop tunes only down to about 650. If listening below
these frequencies are important, you should add a switched 150 pf capacitor.
Overall, this loop turned out very well. It sure looks nice.
 Tape stuck to plastic for hole position marking.
A center line was also added.
Loop antenna center hub.
Wire and tuning capacitor detail.
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