Fan Dipole

I’ve built a number of Fan Dipoles over the years and have found them to be quick and simple to build up.  These are photos from my first antenna and it was in the air for 4 years.  Photos below show my 80-40-20-15m 3 element antenna, 15m being a 3rd harmonic of 40, and you can click on them to enlarge.  This is not intended to be a detailed how-to but rather a construction guideline.  An analyzer makes this simple but you can do it with pencil, paper, and SWR meter just as easily.  Substitute materials as you see fit but if you use coated or insulated wire instead, adjust lengths accordingly.

 

Bill of materials for a 5 band (80-40-20-15-10m) 4 element Fan Dipole:

Qty 265′ 12GA copper stranded wire from your local source

Qty 1 1:1 balun

Qty 1 Ikea cutting board (or similar)

Qty 8 egg insulators

Qty 12′ 1/2″ Delrin rod (any plastic will do, Delrin resists UV breakdown) Note that fibreglas rod breaks down over time and will become a maintenance hassle.

Qty 10′ 14GA copper wire solid

UV resistant ropes to hold up the elements and for tag lines.

 

Original concept drawing for 3 elements and 4 bands.  Red = elements, Black = ropes.

 

Cut wire into lengths as follows: 2x 70′, 2x 35′, 2x 17′, 2x 9′

The cutting board ensures the elements don’t come into contact with the supporting structure and give some strain relief to the elements as they attach on the balun.  See photo, mount Balun on cutting board.  Drill holes to provide strain relief to the wires coming into the balun.

Top centre of Fan Dipole

 

Cut Delrin rod into 4 lengths – 2×3′, 2×2′, 2×1′.  Drill 1/8″ hole at each end.  Drill two 1/8″ holes evenly spaced on the 3′ lengths.  Drill one 1/8″ hole in the middle of the 2′ length.  You should have 3′ rods with 4 holes, 2′ rods with 3 holes and 1′ rod with two holes.  You will pass the wires through the holes that you drilled in the last step.

Working on one side at a time, connect one end of the elements through the cutting board support holes and to the balun.  Once you have the elements laid out per the drawing and the spacers laid out in place, use the 14GA solid copper wire to secure the elements in place so the spreader rods don’t slide around on the elements.  You require a spreader where the end of a shorter element meets the midway point of a longer one above it.  Repeat for the other side.

Secure an egg insulator at each end but allow 6″ (10m element) to 2′ (80m element) of excess wire to hang below the insulator to allow for tuning.  This small length of wire at 90 degrees to the main element won’t detract from its operation in any meaningful way, and allows you to tune and prune easily without having to move the spreaders around.

How to secure a wire to the spreader

At this point your construction is complete.  Hook up feedline and hoist it into the air to tune it up to your favorite part of each band.  Start with the longest element and work to the shortest.  I always hoist up the ends and midpoint with a small diameter rope and a pulley as it makes the tuning step and later maintenance simple to perform.  Tune the 40m element to 7100kHz and it will be a nice 3rd harmonic on 15m around 21300kHz.  I tune mine to 3700kHz, 7100kHz, and 14175kHz which allows me to cover off the upper end of the CW range and well into the voice range of each band.

Mid-point photo showing centre

The little “tail” seen hanging below the 20m element is a tuning stub.  Simply wrapping the wire back upon itself to shorten it is sufficient instead of cutting.  In the event you fold back too much, unlike cutting/pruning, it’s easy to unfold and try again.  In later versions of this antenna I’d hang a few ounces of weight here to stop the wind from grabbing the end and wrapping it around the upper elements.  Alternately you could use a tag line to loosely secure it at ground level.

Side view of mid-point

When most people cut elements for a dipole they ensure they are the same length.  I don’t as I want them slightly different up to a few inches for lower bands.  In this way the antenna is slightly more broadbanded versus having a perfect SWR within a narrow range of frequencies.  I’m perfectly happy with having the low point of SWR at 1.3:1 and a 2:1 bandwidth of 100kHz on 40m versus conventional thinking of low SWR 1:1 and 2:1 bandwidth of 50kHz.

FW Fan Dipole now 3 bands These are my original notes on the project I emailed to a friend in 2009.  Links within this .pdf will take you to the sources of my inspiration and a bit more detail behind the construction.

I hope you’ve enjoyed reading this as much as I enjoyed building this antenna.