J-Pole Antenna
 


I know there is a lot of text here but it is important to help you build this simple but good antenna. Take time to read it. The J-Pole antenna is fundamentally an end-fed 1/2-wavelength antenna that uses a 1/4-wavelength long transformer section to supply the very high feed voltage. Average gain with a 155 MHz meter J-Pole is about 3 db. The J-Pole is that it is at DC ground, so it can be mounted just about anywhere and still work. This design is very rugged and can be built for a few dollars with most of the parts available at your local hardware store.

The construction of the J-pole antenna is fairly easy. You will need some 1/4" Copper pipe, (2) 1/4" copper pipe caps, (1) 1/4" Copper 90 degree elbow, (1) 1/4" Copper T connector, (2) stainless steel clamps and the necessary length of 9913 coax cable for each antenna. Note: Use 1/2" copper pipe for the lower bands 290 MHz and lower, the 1/4" will be too thin for support.

This is a direct feed antenna. I could be wrong but I prefer not to use a matching device but design and build the antenna to match directly. To me this means more efficient transfer of energy and better performance, again some may argue this point but I have always strived from HF to 2.4 GHz to direct feed when possible.

Cut the copper pipe to the appropriate lengths (see my notes for lengths). Note, the dimensions are metal to metal measurements, NOT center to center. Once the pipe is cut, clear the ends of the cut pieces of burrs. Test fit all the pieces to make sure they fit, and re-measure your lengths. Clean the ends of the pipe, and flux. Solder each piece together minding the alignment of the elements as you go. Don't forget to solder the caps on top of the elements too. Once the copper has cooled from soldering, add the stainless steel clamps to the upright elements. Mount the antenna in the location of your choice with two stainless steel hose clamps . Next run the 9913 coax cable to the antenna. You will need to connect the braid of the cable to the shorter upright element, and the center conductor to the taller upright element using the stainless steel clamps.

Just a couple of notes to help you get more from your antenna, if you can get this antenna on your roof or tower, about 20 feed up to clear near by trees and houses it will work fine, much higher will only help a little and coax loss can be a issue so I suggest about 20 feet above your house as the best location. Keep the antenna away from trees, metal and wired, mount it in the clear as much as possible.

Use 9913 Coax on all of the frequencies, the line loss on the lower frequencies is not bad but it is a real issue at higher frequencies (
click here to see a loss chart), this is not the place to try to save, use 9913 or hard line if you can.

I do not suggest using a splitter to feed single band antennas to your scanner, these are made for one band but will receive local signals from others, either use a single band antenna on your most listened to service or just use it when you really need improvements on that band and use a all band antenna for general listening. The losses on a splitter are too high and they take back all the gain you make with these antennas. These are omni, you can get even better performance if you build a beam antenna and you can find the plans for them on the internet.
 

Happy scanning.
 


Dimensions

For 860.000 MHz - A = 9.84 inches, B = 3.24 inches, C = 0.36 inches and D = 0.36 inches.

For 407.000 MHz - A = 20.76 inches, B = 6.84 inches, C = 0.72 inches and D = 0.60 inches.

For 460.000 MHz - A = 18.36 inches, B = 6.12 inches, C = 0.60 inches and D = 0.60 inches.

For 290.000 MHz - A = 29.16 inches, B = 9.72 inches, C = 0.96 inches and D = 0.96 inches.

For 130.000 MHz - A = 65.04 inches, B = 21.60 inches, C= 2.16 inches and D = 2.04 inches.

For 146.500 MHZ - A = 57.72 inches, B = 19.20 inches, C = 1.92 inches and D = 1.80 inches.

For 155.000 MHz - A = 54.60 inches, B = 18.12 inches, C = 1.80 inches and D = 1.68 inches.

For 42.000 MHz - A = 201.48 inches, B = 66.84 inches, C = 6.60 inches and D = 6.24 inches.

 

 

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