The " Awesome T " Antenna

Rusty Thu, 08/23/2018 - 15:23

Here is a quick DIY on making a versicle antenna for the RC hobby. It can be used for RC control, FPV video, data telemetry, or any other radio function really. I call it the "Awesome T" it's awesome cause it can do so much and is super simple to make. And by varying the length of the elements, it will work on a wide range of frequencies. Follow along as we make one.  [Picture of finished ]

The parts list for the "Awesome T" antenna

  • RG316 coax jumper with SMA connectors on each end
  • Some wire for the elements, just about anything works.
  • Some heat shrink to cover your wire, and to add some rigidity
  • Liquid electrical tape
  • Hot glue (optional)
  • Center support section (optional)
  • Basic soldering tools and a sharp hobby knife
  • A ruler with 1/16" markings, or better yet, calipers ( for higher frequencies)
  • A volt meter with continuity test function ( you should have one, everyone in RC / FPV needs one)

Parts for Awesome T


The coax jumpers can be found all over Amazon and E-Bay. What you are looking for is a jumper that is long enough to go from your radio to where you want to place the antenna plus 1-2 inches, or just build one with a short stub of about 3-4 inches, then you can use an extension coax later. What I like to do is get a jumper of about 8? inches and cut it in the middle, giving me 2 stubs of about 4 inches each. For the elements, any wire will work, it really depends on how long the wire will be, we will get to that in a bit,  and what you plan to use it on.  I am building this one for UHF RC control , openLRS in the 430 MHz frequency band to be specific.


How long are the wire elements on the "Awesome T" antenna

How long should you make the wire elements? This depends entirely on what frequency you intend on using this on. The formula for this is very simple:  Wire length in inches is  468 / Freq(MHz). This will give you the total length of wire, divide that by 2 to get each leg length, in inches. I cut my legs about an inch longer and will trim to final length once assembled.  So going through the math, An "Awesome T" antenna designed for use with open LRS, with a center frequency of 435 MHz gives a wire length of 1.08 feet or about 12.91 inches, I'll cut it to 15 inches, then cut that into two 7.5 inch legs.

Preparing the coax stub for the "Awesome T" antenna

To prepare the coax for the antenna is fairly straight forward, you just need some basic soldering skills. If you haven't by now, cut your coax jumper to length, but make sure you leave one of the connectors in place.

Awesome T Coax stub








Then take a sharp hobby knife, I use a Xacto blade #11, and measure back roughly 1/2" back and gently roll the coax under the blade. Just set the coax on a cutting surface, place the blade across the coax and roll. You just want to cut the outer most insulation off, doesn't take much. Once you rolled it back and forth a few times, use your fingernail to grab the coax at the cut line and pull of the outer insulation. It may take a practice run or two to get right. if you cut the outer braid off, start over.






















Now that we have a clean section with the insulation removed, just quickly tin the outer braid with some solder, doesn't take much here either, just make sure you go all the way around, and let it cool.















Once cooled take your hobby knife again, and at about the mid way point score the outer braid you just tinned. The idea is to cut the braid and slightly score the dielectric insulation between the braid and center conductor, DO NOT CUT THE INNER WIRE! the inner wire is somewhat thin and could be damaged easily. Once you have cut the braid and scored the dielectric, hold the coax in one hand and with two fingers on the other hand try to twist the very end of the coax off. it should twist right at the point where you just made the cut. If it doesn't twist easily, score it a little more with the knife. A sharp blade works best.



Awesome T Cutting tinned braid








Awesome T After cutting braid











Once you have exposed the center conductor, gently twist it and tin it up. Once the center is tinned, bend it 90° to form a small "L".  The coax is now prepped. This is probably the hardest part of the project, getting this right. it may take a try or two to get the feel of the knife cutting the various materials, but once you get it, it becomes easy.















Attaching the legs to the "Awesome T" antenna

Take both wires to be used as the legs and strip about 1/2 of an inch off one end, and tin it. On one of the legs bend the tinned part 90° to form a small "L", leave the other one straight. Trim both these to leave about 1/4 of inch exposed.

Now take the wire with the "L" and solder it to the outer braid, you might need a small drop of solder to make a secure joint. Then take the other wire and solder it to the center conductor, again a little extra solder helps. Be careful, DO NOT BRIDGE the inner conductor to the outer braid








At this point we have a working antenna, but not at the right frequency. We need to trim each side to the length we calcilated above (12.91" / 2 = 6.46"). So grab a ruler or better yet, caliipers if you have a large enough size, and trim each side to 6.46 inches. Measure each from the center of the coax cable, and that is it. So now we have a working "Awesome T" antenna at our desired frequency. All that is left to do is insulate the center and reinforce it. This is where each antenna can be customized to the specific application. I have a similiar antenna (actually two, one for RC control and one for telemetry) on  a Bixler 2 and it has plastic "T" at the junction point of the coax and wires. The plastic servees to insulte and support the center, but it can be a little bulky for some smaller models. They are also made with a thicker wire for thwe elements. in contrast, I build one for a ZOHD Dart, and there is no way to install an antenna with the plastic "T". I had to use liquid electrical tape and insulate the center, then use some hot glue to build up some reinforcement.


Horizontal or Verticle mounting for the "Awesome T" Antenna

How should the Awesome T be mounted? For the best performance the "Awesome T" should be mounted vertically, as opposed to horizontally. When mounted vertically the radiation pattern is such that the signal radiates (and recieves) much like a donut, round in all directions, but limited performance directly above and below. If it was mounted horizontally the pattern would be similiar but rotated 90° so that a null would be directed to the sides of your aircraft. This would have the undesirable effect of pointing a null at your ground ststion everytime you traveled perpenducular to the ground station. At close ranges you might not notice, but further out, or in noisy enviroments, it will be an issue.

I will cover the thoery in the "Awesome T" antenna in a future article....




So basically you are just ripping off TBS, classy