Posted: 8/27/2008 8:56:40 PM EDT
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any easier, quick designs for a J-pole? Cant find mine.. Can a j pole be made where you can use a run of coax with different lengths of coax? neez |
www.fiu.edu/orgs/w4ehw/j-pole.html www.educypedia.be/electronics/antennajpole.htm |
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I've made two j-poled from copper pipe. One worked exceptionally well for a year before it was replaced. The hardest problem I had was welding the connector to the pipe. Takes a mighty hot torch and you end up melting the dielectric in the connector. Maybe I was doing it wrong. -Foxxz |
I just didn't bother with that. I attached the connector with the circular pipe o-ring fastner thingies... (the correct name escapes me right now.) It seems to work just fine with my 2m J-pole. I was able to hit a repeater a good 25 miles away on 5w, though I do need a more permanent feed point solutionfor when I put this on the roof... |
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J-poles are easily soldered with torch and copper pipe, just like doing plumbing. Coax Attachment... Ground goes to the short leg, center conductor to the long leg. You can use hose clamps. You can clamp a piece of plexiglass across the bottom near the attachment points, mount a SO-239 socket, and run your wires from the back of that socket to the attachment points on the J-pole. Run those up and down a little to get SWR as low as practical. The clamps may be used, or you may solder the wires there once the attachment point is determined. If you make the J-pole from 1/2" copper pipe, and need it to be stiffer, before you solder the bottom cap on, slip in a piece of fiberglass rod. If for receive only, or even for transmit, the feed attachment point will be very close to what the calculator shows below. BTW, the bottom 'stub' does not need to be insulated. It is electrically at 0 v. It can and should be grounded. Here is a calculator, just enter frequency: www.hamuniverse.com/jpole.html Here is a Youtube howto: www.youtube.com/watch?v=bdzuhzT_TE8 And for 2 meters, here is a neat twinlead & coax antenna that may be used in the attic, rolled up for an easily portable antenna, hung up in a tree, whatever. This is a "Slim Jim" design that is closely related to a J-pole. www.hamuniverse.com/2meter300ohmslimjim.html J-poles are very poplular for 6 meters, 2 meters, and especially the FM radio band. Edit to add: You can also make the twinlead Slim Jim, place it inside a pvc pipe with a cap on the top. Connect the feedline to a SO-239 socket on the bottom cap. Seal it all up. Now you have a weatherproof antenna that is rugged. Just screw your feedline to the SO-239 socket. On the other end you can have a BNC or whatever connection you need for your xcvr or handheld. UPDATE!!! I just got my ham license. I was just about to go buy some more copper pipe and break out the torch, but at a hamfest I saw one of these: www.b-squareengineering.com/jpole.htm Being tired and in a hurry, I bought one. For $40, you just can't beat the price. And it's made from stainless steel. I checked in with an ARES net on a repeater 45 miles away using only 8 watts. It was a little crackly, they said, so I went to 12 watts and that cleared it up. |