SIMPLE ¼ WAVE ANTENNA FROM PL259 (SOT239)
A VERTICAL ANTENNA FOR ALMOST NOTHING IN A FEW MINUTES
QUICK, CHEAP AND NASTY ANTENNAS
These antennas can be made from 2m (144MHz) upwards unless loaded with some sort of coil. Even so, they won't take a lot of weight and are really best suited for 70cm (430MHz) upwards. That includes UHF CB. At 70cm though, they could be loaded with a coil to make a 5/8 wave antenna.
A friend of mine gave me some really good advice. "Make evrything from the radios to amplifiers BNC and, from amplifiers to antennas, N connectors." I now have a heap of patch leads for PL259 and a heap of spare SOT239 chassis sockets. This is how I used some of them up. In any case, SOT239 sockets are cheap enough as a base, you can build your own homebrew antenna for a lot less than purchasing one.
PHYSICAL DESIGN CONSIDERATIONS
The mounting holes for the PL259 chassis sockets are made for accepting M3 bolts and nuts but accept a thread with an M4 tap very well. No nuts required. The ground plane units are 6m copper tubing obtainable at plumbing supply stores. The central radiator is made of hard silver solder, the sort plumbers use for copper. It has good strength in the wind and conducts a lot better than things like stainless steel. Another option if not using it on the car is 2.5mm or 3mm copper. This can be straightened and work hardened by putting one end in a cordless drill then running along its length with your fingers bending it across your thumb. Copper is not only easy to anneal (simply heat to red hot then cool) but easy to harden as well.
The 6mm copper tube was beyond the structural strength of the chassis socket for 2m but the length on 70cm is much shorter and the same 6mm copper tube used for the groundplane works well for the central radiator. I was told the 2.5mm wire was not heavy enough to withstand the wind but it has stood the test recently in very windy weather. Nevertheless, with a length of near half a metre, the 2m band is about the limit for making this kind of antenna mount. At any lower frequencies, the radiator is much too long to be held securely by the socket.
To add abit of strength in the case the antenna is hit by a pelican or low flying aircraft, the centre pin of the sot239 and hard solder radiator can be strengthened by adding a collar made out of 6mm copper tubing. I have only bothered with the 2m (144MHz) antenna. Since I only use this antenna for local repeaters, I have also taken a bit more time and tuned it to 145MHz which also gives me a good tune on 435MHz. I still use my yagi for more distant repeaters.
ELECTRICAL DESIGN CONSIDERATIONS
The length of the central radiator is critical. For 6mm tube, the lengths will be much shorter than for some sort of wire. If wire is used, it is better to cut it longer then trim it using a SWR meter to test as you go. It would be impracticle to give measurements because 1.25mm wire will have quite a different length than 1.2mm. Using 6mm tube, the length for 144MHz is 486mm.
The length of the four bird perches should be about the same as the radiator.
This page details what I did but you may want to modify the design for your particular circimstances. The central plate the socket mounts to was made from a square piece of 3 or 4mm aluminium 90mm x 90mm. The ends of the ground plane radials were flattened in a vice and holes drilled to match both the PL259 socket and the outer supporting mounting hole. Extra strength is required for the 4 bird perches on 2m but for higher bands the radials will be short enough to be mounted on the socket alone. Other than that, construction is simply as shown.
Once finished, goop up the top around the PL259 with hot melt glue. See the car antenna for 2m.
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I think that's pretty fair, don't you?