SO239 with nut is a variant that can be used to make an HF Dipole Wire Antenna without having any centrepiece. All you need is just a Screw, a couple of washers and nuts, solder and wires of course. I tested this antenna for two months with my Yaesu FT-840. I transmitted with 50 watts and 100 watts on FT8 and was able to get all the continents.
I also transmitted a full 100 watts on SSB and got fantastic reports from Europe, South Africa, and Japan. I then transmitted 5 watts on WSPR (Weak Signal Propagation Reporter) through WSJTX 8 times a day for two weeks (20 Mtrs). It’s a great community that helps you test your antenna. Even if you do not have any digital setup or an HF radio. Just get the WSPRLite, for testing your antenna, and you are through. In only 5 minutes the WSPR community website will be able to tell you on the map, where all your signal were received.
So, here is the step by step process of making an HF Dipole Wire Antenna without a centrepiece for 14 MHz or 21 MHz Ham Bands.
1) Buy one SO-239 with Nut.
2) Buy a 1 inch long Brass Screw (M3 Size) and cut the Head with Hacksaw blade. If you in Mumbai, go to a shop ‘A. K. Nimakwala‘ at Lohar Chawl. It will cost you around Rs. 5 or 6, but you will have to buy a minimum of 1 dozen.
3) M3 Size brass screw’s head cut
4) Using a file, make the screw pointed (Headend) so that it can go deep in the SO239.
5) Insert the Screw (Pointed part) inside the SO239 and solder it well.
6) Use a Shrink Sleeve on the solder area and apply heat.
7) Take one sq. Mm copper (18 Gauge) wire for the dipole antenna (length should be as per band requirements). Now remove five cms of its shield and take one turn of the screw (as shown in the image below), and check the size of the hole that we want, before we tin the wire.
8) Repeat the above step for checking the size of the nut tracks, as shown in the image below.
9) Once we get the hole sizes, all we have to do is tin that area.
10) After we tin the area, we now insert the shrink sleeve from the other end and apply heat.
11) Now we have to test the sizes of the holes by putting the antenna wires in the screw and on the SO239 tracks, as seen in the image below.
12) If the antenna elements can slip in smoothly, all we have to do now is use the washers and nuts to make it tight.
Please Note: When you buy SO239 with Nut, it comes with two washers. So insert one first, then the antenna wire, and then the second washer, finally applying the nut.
While on the Screw above, put one washer, then insert the antenna wire, put the second washer and then apply two nuts one upon another. Set both the antenna elements in the opposite direction before you tighten the nut.
Make sure you anchor your antenna elements properly.