Dual Band VHF/UHF Slim Jim Antenna

J Pole Links

2 Meter J-Pole Antenna Build

2m 70cm j-pole antenna construction plans

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Check out the New! The design uses a matching system like a j-pole antenna. I started building these antennas and selling them because I saw no one else with a commercial product like this and I figured that I would help fill a gap.

The antennas have become a great success thanks to a lot of hard work and some very dedicated customers. Before I get into the specifics of the antennas I first want to thank everyone who has purchased or helped promote this wonderful product.

Without you none of this would be possible. The basic Slim Jim is an end fed folded dipole. It has a radiation pattern peaking between 5 and 8 degrees above the horizon.

It is this and this alone that makes this one of the best terrestrial communications antennas I have ever seen for the price, 2m 70cm j-pole antenna construction plans. The layout of the antenna is as follows.

The antenna is fed near the bottom and the feedpoint impedance is 50 ohms, 2m 70cm j-pole antenna construction plans. Ladder line was an excellent choice for these antennas as it presented two well spaced parallel conductors and is virtually indestructable. You can hang the antenna in many places. The only exception is near metal objects. They will interfere with the tuning and performance of the antenna.

Hanging it up against drywall or plaster as many people do will also affect the antenna but if this is your only option it will still perform adequately.

Open free space is the best of all options and as with all antennas will yield the best performance. Enter the Dual Band antenna. After many requests for a dual band version of this antenna. I searched the internet and books high and low to no avail. I then began research on what it would take to make this antenna perform well on 2m and 70cm. What I came up with was a trapped end fed folded dipole. 2m 70cm j-pole antenna construction plans antenna acts like a slim jim on 2m and a jpole on 70cm.

The secret formula I will leave for the history books. But this design yields excellent results compared to many other dual band antennas, 2m 70cm j-pole antenna construction plans.

The best I can tell there is no compromise to the performance on 2 meters in fact some claim it works better on 2 than the single band vhf I have yet to scientifically prove that.

Some ask well dont j-poles resonate on the third harmonic of mhz anyway? First this antenna is in the j-pole family but is not a true j-pole. If anyone tries to sell you an un-modified j-pole and says it is a dual band antenna they are steriods and breast cancer they dont work, I have seen swr of 3: Here is the 2m 70cm j-pole antenna construction plans side.

And the plot Just a little disclaimer here this plot was taken with N connectors throughout the system. Your mileage will vary a bit with other connectors. There should be very little pressure in the antenna. This can be achieved a number of ways. It is easier to bow and does not keep as much pressure on the antenna. The 2nd method is to pre-bend the bow. This can be achieved by overbending the bow with string wire or rope and then putting it in the hot sun for a few days or using a heat gun to permanently shape the plastic.

Here is a photo that one of my customers sent me about pre-bending the bow. Original BOW info One thing I get a lot of requests for is a way to rigidly mount this antenna for mast or tower mounting. Most people want to mount the antennas inside pvc. This makes them extremely hard to tune because the velocity factor of pvc is not predictable. I have developed a solution that may not be the prettiest but is 2m 70cm j-pole antenna construction plans usable. I call it the bow and anyone can build one.

Basically you drill holes in the ends of the long piece of pvc and bow it to the length 2m 70cm j-pole antenna construction plans the antenna and zip tie the ends to the holes you just made. Here is a photo of mine on my tower, 2m 70cm j-pole antenna construction plans.

Introducing the flag mast It is kind of a bad photo but this is an atv flag pole with the antenna attached. This is still not the perfect answer to rigid mounting but it is pretty good.

This makes it very easy to come up with a mount for the antenna. You can also use a fishing pole the same way but if you want a permanent roof installation I would stay with the flag mast.

And now the bad news Before Antenna in open space. After Antenna attached to flag mast.

 

2m 70cm j-pole antenna construction plans

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