For hams who like to play VHF / UHF, most like to make their own antennas, and there are more than one pair, because in the V / U section, the quality of the antenna has a great impact on the transceiver effect, and the loss of the cable is also Very powerful, this requires the antenna to have as much gain as possible.
Anyone wants to make the antenna with the largest possible gain, but our most common good effect is Yagi or HB9CV, they are directional, if you want to change the receiving direction at will, you have to install a rotating motor, but often missed Signals from other hams in different directions. What we need is an antenna capable of 360-degree monitoring / communication.
The most basic omnidirectional antenna is a 1/4 wavelength ground antenna, its gain is 0DB, then 1/2, 5/8 wavelength (3DB), and the higher gain is the FRP antenna, but whether they are used Coaxial cables are made in other forms, and they all have problems such as excessive size and troublesome adjustment.
SLIMJIM antennas have been introduced in many places recently, and they are generally well received. Of course I have to try them.
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1. This antenna is really very simple, don't look at it being folded back more than the J-type antenna, but it obviously increases the mechanical strength of the antenna, and it can stand better when making a 2 meter antenna.
2. I choose materials based on the principle of easy purchase, cheap price / portability. Because of the large size, VHF uses a single aluminum alloy slot with a cross section of about 12mm. It is enough to buy 3.2 meters at an aluminum alloy material store, which costs 5 yuan. (Pick a thicker material)
3. Prepare two small crocodile clips, which are soldered to the core wire and the network wire of the 50 ohm cable, and the other end is of course connected to the plug of the transmitter.
4. In the four dimensions of A / B / C / D, use a hacksaw blade to saw the two wings of the single slot, taking care not to cut the bottom edge of the single slot.
5. A / B / C / D Four parts to be folded back, gently clamp the two wings of one side of the saw slit with pliers, so that when folded back, the wings on one side snap into the two wings on the other side.
6. Finally, leave 25mm in the notch, cut off the excess single slot, find a section of insulating material with a diameter of about 10mm and a length greater than 5CM, such as wooden strips, buckle into the single slot at the open end, and fix it with insulating tape .
7. The 50-ohm cable with a crocodile clip is clamped at the feed point X / Y in the figure, and the whole antenna is fixed on a wooden stick with insulating tape. Standing in a more open place, you can measure the standing wave and adjust the crocodile clip The position on the antenna minimizes the standing wave. Friends who do not have a standing wave table can use the method of receiving signals to receive signals near 145MHZ and look at the S point of the receiver until the most S points are received.
8. Make a mark at the feeding point of the adjusted antenna, use two aluminum alloy screws to screw into the single slot with self-powering screws, and remove the crocodile clip from the core / net end of the feeder, peeling off a small section of the self-powering Screw on the screw and tighten finally, just fine. My antenna feed point, the net is connected at 75mm from the bottom, and the core is connected at 90mm from the bottom, the minimum standing wave measured is 1.1.
9.When the antenna is erected, it cannot be fixed directly with the iron pipe.First fix it on a section of wooden rod, and then fix the wooden rod on the iron antenna rod.
10. The reason for the high gain of this antenna is that its radiation elevation angle is very low, approximately close to horizontal, while the radiation elevation angle of 5 / 8GP is approximately 30 degrees.
11. Try it out quickly. I used this antenna that I made in a while and compared it with the 1/4 ground network GP, and achieved a noticeable effect. The antenna resonating at 145MHZ also received the signal when receiving the aircraft signal near 128. Unexpected good signal.
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| Do not cut the material first, wait for the shape to be folded, and then remove the excess. | |
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