RCARES JPOLE

From Megawiki

1 What is a J-pole?
2 Assembly
3 Parts List
4 Time and Cost
5 Finished picture

What is a J-pole?

A J-pole is a 1/2 wave or better antenna. What does that mean? It has gain. A homemade copper J-Pole antenna is mounted is tuned for best VSWR by moving the feed point up or down along the pipes, and then soldering in place.

On mine, I had to slide the feed point all the way down, and the lowest VSWR point was still not in the middle of the 2 meter band. It's very good, but not perfect. I would recommend that you start with each pipe being 1 or 2 inches longer than the book calls for, and tuning the antenna before soldering the caps on the pipes. Then you can trim the pipes if needed. This type of antenna is cheap, easy to build, rugged, and is an excellent performer. It is omni-directional, and can be made portable or permanently mounted. It can be grounded, so it is quiet, and somewhat lightning protected.

This antenna needs no impedance matching if used with 50 ohm coax, since its resistance/reactance appears as about 50 ohms. The simple BALUN is made from several loops of RG-8 coax, if needed.

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Assembly

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Cutting and Fluxing

Cutting station uses a measure, pipe cutter tool, permanent marker, steel wool. A two meter / 440 design uses the following measurements for resonance at 145.610 MHz. The dimensions are 60" piece, 2" piece, and 20" piece. The remainder is used to support the antenna below. the T piece.

The pieces were made a little longer than normal because of the frequency chosen for resonance. One can always cut them down to length, it is hard to glue length back on.

Once cut all the pieces are shined up at the joints. ( real key here). Fluxed up with fluxing paste. This concludes the cutting and fluxing station. The assembled form is then brought in one piece to the soldering station.

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Soldering

Since the advent of Lead free solder higher heat is needed to join these sections. This station usually requires a good torch head, MAAP GAS, welding gloves, Solder, outside well ventilate location.

Start at the T section of the J-Pole. This is most critical to heat well and is one of the most important locations to join. Have a Box or sawhorse hold outer ends to support the antenna.

Don't be shy about solder or heating, Good knowledge of soldering pipes is good to know. This is also good practice.

Make sure flame gets a greenish / color hue to it that is when copper is heated well. Then apply solder to the joint it will be sucked in to the joint and form when it cools.

Move to J section 90 degree bend then get that soldered well.

Move to the end caps and screw in connector at bottom.

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Matching

A antenna tuner is real useful here.

The matching section is N9RGX idea, it is sturdy and real easy to make. It is also a lot easier to adjust. The clamps make it a piece of cake, and makes J-pole look almost professional.

First you take the Milford hangers and cut them down so they cross with a tin snips
about 2.5 inches they come out like a V from the pipes.

SO-239 is then bolted to the J part (shield) of the antenna with a stainless #10 bold and nut. a waterproof neoprene washer (dime size) is placed on the SO-239 to separate the hangers

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Tuning

Use at least 50 feet of coax for tuning. Start about 3" up on from bottom of j. go up 1/4 inch at a time. up for higher in frequency , lower for lower in frequency.

once tuned lock hangers down and mark antenna. Just in case.

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Shining and Sealing

Milford hangers and antenna will corrode SO-239 and hangers need to be sealed. I used silicone to make a small pyramid or cone on top of connector (threads down). This keeps water out and other debris.

The Milford joints with screws i filled in connectors with a finger of silicone. Be liberal here. I also coated the cop of the connectors to the so-239

Once dry 24 - 48 hours. I shined up the antenna with steel wool. I put tape on threads and so-239 part. Then sealed antenna for outdoor use with a Krylon or a NON - metallic paint , with 3 coats.

This will keep any antenna shiny and sealed, and clean

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Mounting

You can mount this any way you like you can put a threaded transition at the bottom during solder stage for 3/4" to a flange floor mount. this can be put on a tree stand and or other mounting idea. another easy way to mount on a side of a tower is to take a 2" PVC pipe 5" long. This is bolted with arms or mounting hardware to a tower , and the coax is brought up through the pipe. The J-pole is screwed in and sealed at the coax connection and then coax and antenna slid down until bottom touches PVC. This is easy to mount and works well.

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Parts List

Racine county dual band J-Pole hardware standard 2 meter / 70 cm. See Racine county digital hardware standards document. (Specifications can be used for any band. )

Source Home Depot- Racine 12/01/05

1-10' 1/2" copper PIPE - ~$9.78 EA thick wall preferred.
2-coax clamps 1/2 " Milford copper pipe hangers) - @ $0.99 EA
3- 1/2" end caps- @$0.23 EA
1- 1/2" copper T - @ $0.42 EA
1 - 1/2" 90 degrees - @ $.26 ea
SO- 239 bulkhead ~ $2.00 ea - $3.00

(optional N bulkhead connector )
stainless bold to hold that fits through pl-259

ARES to provided Pipe cuter/tape measure/drill/ solder and flux etc / Torch tank/ knowledge / Tuner ... $3.00 fee for solder / flux / torch. (if you have your own feel free to bring.) KB9MMA will bring MFJ versa tuner to tune antenna.

optional ($2.50) kit 3/4 "floor Flange 1/2" male to 3/4 threaded adapter (copper)

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