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Portable 20 meter vertical




 
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Author Topic: Portable 20 meter vertical  (Read 352 times)
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ka1tdq
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« on: November 12, 2017, 11:16:47 AM »

I wanted to build a portable 20 meter vertical that could break down easily, so I came up with this.  I'm about halfway done.

Everything will come apart by hand.  As seen in the picture, an 8' piece of 1/2" copper pipe will slide over the wooden dowel.  An 8' whip will be attached to the top of the copper pipe.  The wooden dowel isn't affixed and just slides out of the assembly.

Four wire radials will be attached to the copper plate via a wing nuts.  They'll be pulled taught on the ground by rope and small bricks.

I'll have a 1" tall square block that will slide over the wooden dowel to separate the copper pipe from the ground plane.  

The center conductor of the SO-239 will be attached to the copper pipe by a wing nut/bolt.

Jon


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AJ1G
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« Reply #1 on: November 12, 2017, 12:22:22 PM »

Looks like you are planning on mounting it fairly close to the ground.  You could also elevate to feed point to the top of a mast and use the radials and rope extensions of them to support the mast.  I've had my eye on the long telescoping fiberglas painting poles sold at Home Depot for portable antenna masts.
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Chris, AJ1G
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« Reply #2 on: November 12, 2017, 01:15:29 PM »

I was gonna say:  you'll be well served to get those radials a couple feet off the ground.

Well served by the dB gods, that is.

--Shane
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ka1tdq
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« Reply #3 on: November 12, 2017, 01:22:29 PM »

Yeah, why not? Itís just a threaded floor flange on the underside of the copper base. I just need to add an 8í length of threaded pipe to the collection and screw that on too. The radials will serve as guy wires.

The plan was to get something a little more efficient than my MFJ resonator. And like always, my projects start out small and then get overkill. 😄

Jon


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WBear2GCR
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« Reply #4 on: November 18, 2017, 07:27:49 PM »

All things being equal, the copper plate seems excessive, unless you have a scrap pile full of copper plates.
I'd focus on a larger diameter for the vertical = more bandwidth...

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ka1tdq
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« Reply #5 on: November 18, 2017, 09:29:10 PM »

I've run a test with the vertical as-is and mounted on the ground.  It's actually very wide in bandwidth!  It starts out at 1.4:1 at 14.000 MHz and ends at 1.7:1 at the top of the band.  

I haven't posted a picture yet because I'm not finished with it.  I found out that the 1/2" wooden dowel bends too much with the vertical element on it.  I have a 48" fiberglass rod coming in Monday that should correct it.

Also, adding another vertical section would be too awkward to put together.  So, I put rubber non-skid on the bottom feet of the tripod, and the whole thing will sit on top of the car.  That'll give the radials a little extra height above ground.  

The car has an NMO-to-SO-239 adapter, so I'll have a short run of coax going from that adapter to the copper plate.  Electrically, the car will also be in the ground plane.  I'm hoping this has a positive effect.

Jon
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W6TOM
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« Reply #6 on: November 18, 2017, 10:10:45 PM »

  Using the car as a ground plane might just be what makes the difference. A few years ago I built a 20 meter dipole that I wanted to be easily movable, it would be in my backyard which I keep as bare dirt and just rotor till at the end of the rainy season, which is why I need to move it easily. I put 4 radials on it, tuned it for the center of the phone band, the driven element was 15' 1 1/2", match was excellent.

  It did not perform well at all, I was told I needed more radials.


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