Tuesday, June 17, 2014

W8MDE 10 Meter Rotatable Dipole

I spent Father's Day finishing up my 10 meter rotatable dipole antenna project for this year's ARRL Field Day which is coming up in a couple weeks.  I wanted to change things up and try working a different band other than 40 meters where I have operated the past few Field Days.  The sun is putting out as many sunspots as it's going to during this solar cycle so it has the 10 meter band coming open usually every day for world wide communication.  So this and the fact that our club's field day location has a lack of trees for antenna supports I decided to focus on the shortest of the high frequency wavelengths.

This is the second homebrew antenna project I've built since becoming a radio amateur in 2008 and I had a great time with it.  A dipole is a most basic type of antenna and is easy to build.  Dipoles are usually made of wire and strung up between two supports but aluminum tubing can be used for the elements which is what I used so the antenna would be self supporting.

Materials I gathered from my spare parts bin and local hardware store.  I also used a new to me vendor; DX Engineering, to supply some high quality saddle clamps for the mast to Lexan plate connection and fiberglass tubing for the mast.  DX Engineering is located here in Ohio so I can consider all my antenna components for this project locally sourced.  The Lexan sheeting was a scrap piece from work and I fabricated a small aluminum angled bracket to mount the coaxial connector.  The antenna elements are made from anodized aluminum tubing I got at the hardware store.  

The jumper wires are #14 braided copper with crimped and soldered connectors.  The white PVC pipe acts as a support sleeve for the aluminum antenna elements.  I drilled a small hole on each side so a stainless steel sheet metal screw can provide secure electrical contact between the jumper wire and the aluminum tubing.  The feed line attaches at the bottom of the bracket.  In the picture the connector is wrapped with self vulcanizing tape and a cable tie to weather proof it.  Shortly after taking the picture I placed a blob of RTV 100% silicon on the top of the coax socket to further protect the exposed solder joint.  The ground side of the dipole attaches via a ring terminal connected to one of the socket mounting screws.

The cool thing about half wavelength dipoles is that the physical length can be approximated by a simple formula:  468(ft) / frequency (MHz).  I wanted my antenna to be resonant on 28.050 MHz so 468 divided by 28.050 equals 16.684 feet. That number should be close to the overall length of the antenna.

I designed the antenna elements using 6 ft sections of tubing with a smaller diameter 3 foot section that telescopes into the bigger piece.  This allows me to adjust the length of the element legs in or out to set the point of resonance of the antenna just where I want it.

With the help of my antenna analyzer I noted the SWR then extended the ends a couple inches at a time and rechecked the antenna with the meter.  After repeating this process a few times I observed the low point of the SWR curve move right into the area of frequency I plan to operate.  I locked the element tips down tight with a small hose clamp.
SWR Curve

27.062     1.5
27.303     1.4
27.573     1.3
27.955     1.2
27.968     1.1
28.197     1.1
28.208     1.2
28.622     1.3
28.902     1.4
29.180     1.5

I'm sure most hams would agree the most exciting part about making your own antennas is hooking up the rig and seeing if one can actually make a contact using the homebrew equipment.  It was late in the afternoon when testing was complete and I headed inside to my operating position to hook up the antenna to my transceiver.

Right away I heard signals coming in so that was a good sign.  I set my dial to 28.076 MHz and sent out some CQ calls using the digital mode JT-65.  After a few tries with no response I looked for a station who was calling.  Up popped a ZL prefix station on the decode screen which I recognized as one from New Zealand. It took two tries and on the second go ZL4AD received my signal and we completed the quick JT-65 contact spanning 8,811 miles between us.  

With that as a first contact I'm going to call this antenna project a success and I think the thing will work fine for making a few local stateside contacts during the Field Day event.


  1. Dear Mr. Theorist,

    You are alright! I can't get into ham radio right now--too much on my plate with life commitments, bicycles, & film photography.

    But I give you much respect for your work!


    1. Thank You David,

      I got into ham radio in 2008. Since then its been one of my favorite hobbies. But yeah its hard to find the time especially in summer when I'd really rather be outside riding my bikes. As it turns to fall and the daylight gets much shorter is when I spend more time in the ham shack.

      If you ever have a chance I highly recommend amateur radio. It is a very rewarding and interesting pass time. I always wanted to do it since I was in my 20's but I never got around to it always figuring I'd get my license when I was an old retired guy. I'm glad I didn't wait and went ahead and pursued it.