WrightwoodCalif.com Forum
Public Forums => Radio Talk => Topic started by: kew on Mar 21, 07, 11:37:00 PM
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I have a really stupid question.
Left over from my CB days, I have a very good mobile antenna, similar to a Firestik.
(http://www.firestik.com/images/kw-antna.gif)
From a PRACTICAL stand point, can that antenna be tuned for use on the 2 Meter band?
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Since CB is in the 27MHz area and 2 meter is in the 145 MHz area, I suppose you can cut that Firestick and use a SWR meter to see what you got, but it sounds pretty iffy to me.
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Ken....in one word....NO.
That antenna can not even work on 10mtrs. without an antenna tuner and even then it would not be efficient. The take off angle of transmission used of out of band antenna's is the problem rendering it useless. That's where people have a missconception of antenna tuners to load the antenna to any frq. out of band.
Best to buy an antenna intended for the band being used. Quality multi band antenna's operate very well albeit expensive. In some cases better than a mono band antenna......depending on if it's a 1/4 wave , 1/2 wave 5/8 wave etc. :thumbs:
May I recommend the ARRL antenna handbook which will explain and may confuse, but non the less very infomative. I use it for gathering formula information on constructing wire antenna's to machining my own yagi's for HF or VHF-UHF work.
It also has a very good Smith Chart and velocity/gain loss factor chart for coax.
Without that book I could never have made my own coils for 160mtr.s for a field day antenna.....double points for 160mtrs. ;)
73,
WB6K
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Since CB is in the 27MHz area and 2 meter is in the 145 MHz area, I suppose you can cut that Firestick and use a SWR meter to see what you got, but it sounds pretty iffy to me.
No it's top loaded....cut it off and then toss it in the trash.
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Yeah. What Mike said. NO.
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Since CB is in the 27MHz area and 2 meter is in the 145 MHz area, I suppose you can cut that Firestick and use a SWR meter to see what you got, but it sounds pretty iffy to me.
No it's top loaded....cut it off and then toss it in the trash.
See, that's where the General and Advance tickets come into play. ;D
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Although come to think of it, in theory you could cut off all the heat shrink, unwind the copper coil, recalculate it for two meters, re wrap it. It has to be a correct turns ratio of helical wind to work. Cut of the several inches of fiberglass you won't need. re heat shrink it, and then it might work. But like Mike said, toss it in the trash.
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And that knowledge has nothing to do with being a General or Extra. And there is no Advance ticket anymore.
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And that knowledge has nothing to do with being a General or Extra. And there is no Advance ticket anymore.
See, I would have gotten that question wrong if it were on the test I took! ;D ;D My understanding was that the upper classes had more to do with antenna theories, etc.
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Laughing...you are going to have to be punished :eyebrows:
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I think his punishment should be to build a few antennas and it will all come together.
I have the formulas on a note pad on my 18 element 2mtr. ohased stacked yagi's and 23 element 440 yagi's, for SSB work I've built.But we should make him suffer and figure it out on his own. ;D
Then when he get's that down....lets let him make a 40mtr. dipole resonant in the middle of the band.
Ok...I guess it was his turn in the barrel.....sorry dude. But it is good learning experience. ;)
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Never argue theory with electronics geeks... :2thumbsup:
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Never argue theory with electronics geeks... :2thumbsup:
I agree....man.... stay away from them e-geeks.
I took special interest into antenna theory because it's more of a mechanical thing in the end for me. Especially machining parts for yagi's and when they work....oh...ya baby that makes me warm and fuzzy. Making the ultimate J-pole from the antenna book out of stainless and delrin kept my at work station going for years.
I must admit, when I had problems with my amplifier I handed it over to the folks of a higher pay scale. I am not in that geekzoid zone that's for sure and I know my limits. ;) I can hook it up and build the ACC connectors and change the tubes and that's about it.
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Thanks guys, like I said in my original post, "I have a really stupid question." ;D But Hey, if you don't ask, you don't learn. :)
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Like Mike I reallly enjoy antenna building. It's more mechanical engineering than electronics and it's something even new hams can do with just a little help. When I was the Pasadena Radio Club prez I used to hold a J-Pole building clinic after each class got licensed so people could build their own antenna. J-Poles are really easy! Ther ARRL antenna book is big and expensive. It include some software for frequency and legth calcs that is quite useful. If you are going to seriously get into ham radio as a hobby -listen up all you new generals- you should the antenna book and the ARRL Amateur Radio Handbook.
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One step ahead of you over on Linnet Rd ;)
I have the software version of the ARRL antenna book and used it yesterday to print information regarding center feed antennas and flattop vs. inverted V dipoles.
Trying to learn what I can about the 90 foot broadband folded dipole antenna before installing it.
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It's a good thing John has a lot of property. Here he is working on his new Antenna for DXing:
(http://www.grimshaw.net.au/images/w0un_40m_top.jpg)
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I agree....the J-Pole is the best place to start for beginner antenna building. The copper water pipe solderes J was the first one I ever built. Then all my buddies wanted one.....jeesh it was a mass production. Not long after, a guy was selling them by the truck loads at the TRW swap meet so cheap the material almost broke even. He must have had imported help to build them. ::) I think I still have a few in the garage if I haven't given them all away by now.
I also agree that the new HF Generals should learn how to cut a wire dipole to resonant frq. Those formulas are covered in the NCT study guide. All it costs is the Balun and some wire....but then you can make your own balun also. Then there is the magical phenomena when you get it up in the air. You ask your self gee....I cut it to the formula, why isn't it resonate in the air?
I'll leave that for you to figure out ;)
No helping Clint ;)
That looks like a 40mtr. mono band yagi at the top....jeesh those things are much bigger than the 40mtr. rotatable dipole I'm putting up soon. And is that a couple 20mtr. stacked phased yagi's for 20mtrs. I think I'll stick with my KLM KT-34XA for a few more years.
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Bob - that stuff in the front yard is nothing!
You should see what's being planned for the backyard :wink3:
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....I think I'll stick with my KLM KT-34XA for a few more years.
Darn straight, Skippy!
Another fun project we could do is a T-hunt antenna, although you can still do a lot with an HT and a cookie sheet! ;D [my turn to let folks figure THAT out!]
When I used to hunt with the Santa Clarita club they did a project with a pre-made instruction and materials kit for a mobile yagi. Simple stuff, just rod, pvc and wire. I stuck it through the sunroof of my Celica and had a 360deg template at the bottom. Worked great and got a lot of looks! ::) My friends that I went with had a quad that he made for their VW microbus, that looked pretty trick, too - got a lot of waves from little kids in passing cars ;D Of course, the trickest I've seen Toolman made, it's a nice little handheld yagi, that's another thought. I've been wondering about interest in T-hunts in town for awhile, I think I'll post a separate topic...
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This site has a calculator for determining the length for each section of a J-pole at any freq.
http://www.hamuniverse.com/jpole.html
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In the March '07 issue of the ARRL QST magazine they revisited making a portable roll-up J-pole antenna for 2 meter/70 cm.
With Clint making it very clear that a lot of HAMs don't know what they are talking about, does this guy know what he's talking about in building a J-Pole Antenna?:
http://www.alpharubicon.com/elect/jpolejaden.htm (http://www.alpharubicon.com/elect/jpolejaden.htm)
It sounds pretty easy!
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I can tell you from expereince that there are many j-pole designs out there, and most of them don't work. One friend of mine WD6DZS compiled an compendeum of j-pole designs and in trying to build them at a workshop not one of them worked! The one I use does not require a balun loop and that's the first time I ever saw one called for.
By definition/design a J-pole is a 1/2 wave over a 1/4 wave measured from the feed point. These demensions look a little off to me but I have not checked them closely.
I don't like the designs that use a mounted SO-239 so this would not be one I would choose. But that's just a personal choice not a design flaw.
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This one isn't backpack portable but if it works it might be good for a near invisible antenna for RVs etc.
http://ka1fsb.home.att.net/jpole.html
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That KA1FSB site is one of the best J-Pole documents I've ever seen!
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Clint - The magnetic base antenna you showed us in class with the small diameter coax. What RG # is the coax and where did you get it?
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Amyone have experience with limited space Slinky Dipoles and inverted Vee Antennas ?
http://www.kbzeroxa.com/the_slinky_ham_radio_dipolei.htm
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Clint - The magnetic base antenna you showed us in class with the small diameter coax. What RG # is the coax and where did you get it?
Ken....if your looking for small coax for car installation or short runs, I personally do NOT use the RG-58 that radio shack sells. I prefer to use RG8-X for mobile installs or runs 50' or less. It has a higher gauge center conductor, insulation properties, and a higher coefficient velocity factor rating. Although the retaining ring for a Pl-259 fitting is available to fit the diameter, .242 = RG8-X vrs. .195= RG-58 you can still use the standard retaining piece by drilling it out. Or simply order the correct fittings when you order the coax. The RG-8X can maintain a tight radius for mobile installations.
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Amyone have experience with limited space Slinky Dipoles and inverted Vee Antennas ?
http://www.kbzeroxa.com/the_slinky_ham_radio_dipolei.htm
Yep...built a lot of inverted vee center fed dipoles. As cheap as baluns are I just buy them. A Van Gordon is less than 20 bucks, but a high wattage balun will run about 75.
Those are what I was talking about in the beginning of the antenna post.
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Clint - The magnetic base antenna you showed us in class with the small diameter coax. What RG # is the coax and where did you get it?
Ken....if your looking for small coax for car installation or short runs, I personally do NOT use the RG-58 that radio shack sells. I prefer to use RG8-X for mobile installs or runs 50' or less. It has a higher gauge center conductor, insulation properties, and a higher coefficient velocity factor rating. Although the retaining ring for a Pl-259 fitting is available to fit the diameter, .242 = RG8-X vrs. .195= RG-58 you can still use the standard retaining piece by drilling it out. Or simply order the correct fittings when you order the coax. The RG-8X can maintain a tight radius for mobile installations.
At our Ham class, Clint had a mobile antenna with a magnetic base and a coax about 1/16" diameter and very flexible.
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Ken that was RG-174. It's horrible stuff and has almost no right to exist. Plus you can't install connectors on it without a special tool. It comes on those MFJ micro mag mounts and they are only suitable for emergencies!Mike's suggestion of RG-8X is right on for mobiles. What Larsen supplies on their NMOs is fine too.
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Thanks you, both. :)
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RG-174. It's horrible stuff and has almost no right to exist.
Well yes you have a good point there for our frq. usage. But it's actually used a lot at the upper frq. ranges in the 3gig and up range. It's used on a lot of spacecraft for telemetry and our RFI thruster EMI testing scientist at work in the anachoic chamber uses it exclusively. It's a pain to put sma connectors on it and "N" connectors.....I know...I make up his cables. :'(
It has no use in our world of frq's that's for sure.
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Since this post is already titled antenna's I won't start a new thread and people can share their antenna information here.
I've heard good things of Delta Loop antennas over the years but never had the space to install one. I've been on the receiving end of many loops and they are quite impressive.
This weekend I completed the installation of my Delta Loop Multi band HF antenna. With the help of Wrightwood, Robert W, Boston Bob and the infamous Johon the tree climber we were able to get about 297' of wire run through the trees at the 35' elevation mark. In my reading and discussing Delta Loop's with other Hams who have used them for HF, the optimum height above ground for Delta Loops is 35-40 feet. The feed point is lower but it doesn't seem to matter much.
The antenna is fed with approximately 50' of RG-214 coax into a Centaur 4.1 Balun. Centaure makes the best in the business for baluns and they are pricey. The balun was 130 bucks several years ago when I purchased it for another antenna brainstorm that never materialized. A 4.1 Balun is used instead of a 1.1 balun because of the impedance of the length of wire. 450 ohm. ladder feedline could have been used but keeping that stuff away from metallic objects would have been difficult. The wire is supported from the trees with UV resisted guy wire material covered in PVC to ward off the critters. The antenna is almost invisible running around the property. If it were not the mast present for the Balun support, no one would know it's there. The wire has enough flex for tree movement during winds without coming in contact with obstructions.
Now for the test. It had surprisingly a low SWR given it wasn't cut for a resonate frq. No surprise there as a lot of Delta Loops aren't. I did not need an external antenna tuner, as the internal antenna tuner tunes it up quickly on all bands from 80mtrs. - 10mtrs. including the WARC bands. Which makes me happy because now I've got a good player on 17mtrs. which is where I made my first contact with it.
Later that afternoon and all the tools put away I sat down for some contacts. With 20mtr.s being my favorite band for DX'ng I started there. I had a few stateside contacts and then came across an opening into Europe. That was a little tougher getting into England and Spain because of the pile up. I'm used to pointing a beam and tossing about 800 watts in one direction. I finally got in and exchanged information. The band died out quickly and moved on to 40mtrs. Another favorite of mine but still haven't got WAS on that band yet. After working several stations with good reports, I think I can easily get WAS on 40 with this antenna in no time. I ran across a three way with a guy in Co. In. and Tx. I joined in with them and they were also giving me some 10 over 9 reports with some 20 over as the band changed. After a while, a few more operators chimed in from back east. Ct. Mn. Ky. and Mi. I chatted with all these guys for about almost two hours and had to peel off for dinner.
I drew up a map of the tree locations and length of wire between the trees. I plan to visit my buddy at work who works at our onsite antenna range and have him plot my theoretical pattern with his mega buck software. I'd like to see what the pattern and take off angles are....just curious to see what it's doing in space above ground. Hopefully he can provide me a .jpeg like he did for my repeater installation that I can post later.
While I like and still prefer Yagi's for HF work I found this antenna especially nice because I could hear everyone without rotating the beam to try and find a neutral direction. It's difficult to point toward Mi. and expect to hear a Tx. station in the group with a HF Yagi.
The most expensive part of this antenna was the tree climber.
I think I'm going to like this antenna. ;D
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PLus the 6,000 foot tower you put the Delta Loop on didn't hurt.
It's Janos ;)
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PLus the 6,000 foot tower you put the Delta Loop on didn't hurt.
It's Janos ;)
Yes proper validation is in order and my bad. ;D
If I remember correctly though, we're using the same geographicaly correct tower...in fact your's is a bit higher...... ::)
Post some of the pics you took whil'st we were having fun impact testing my Dewalt drill from 35'. :-\
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(http://i171.photobucket.com/albums/u284/WildDesertHorse/this_thread_is_worthless_without_pi.gif)
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(http://i171.photobucket.com/albums/u284/WildDesertHorse/this_thread_is_worthless_without_pi.gif)
Every thread has to have a complainer ;D
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Easy Funky.... ;D
John took some pictures while I was praying my Dewalt would live through the day.
There isn't realy to much to see since the wire dissapears in the trees, especially at that height. But you can see the mast and 4.1 Balun mounted on the roof.
He'll get around to posting some after his coffee. ::)
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What pressure.........
(http://www.wrightwoodcalif.com/ham/DeltaLoop2.JPG)
(http://www.wrightwoodcalif.com/ham/DeltaLoop1.JPG)
(http://www.wrightwoodcalif.com/ham/DeltaLoop3.JPG)
(http://www.wrightwoodcalif.com/ham/DeltaLoop4.JPG)
(http://www.wrightwoodcalif.com/ham/DeltaLoop5.JPG)
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Toolman mentioned that he was looking for something that is a little more omni-directional and I wonder if will see this is in his antenna farm in the future?
(http://www.hermann-uwe.de/files/images/antenna_0.preview.jpg)
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Hey! Who let that guy use gaffs on a pine tree?
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Toolman mentioned that he was looking for something that is a little more omni-directional and I wonder if will see this is in his antenna farm in the future?
Great idea.....could you imagine how big that would need to be at HF frq's :o
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Great idea.....could you imagine how big that would need to be at HF frq's :o
Could you imagine how big of a hissy fit everyone would have if you had something like that but for HF freq's lol! ;D
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Looks like a modern artists idea of a Dandelion seed.
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Looks like a modern artists idea of a Dandelion seed.
That's a good one Clint... ;D
So what type of matching network would be used given a 50ohm feedline for this array? It's not a discone, but has almost the same properties, so what is it? Odd I don't see any feed line so what now? What frq. is it being used at? Id say pick any frq. you like and pick a matching network to make it function. It appears to be in the 1.8-2.4 ghz. range but lets say you wanted an array like this on 2mtrs.
Would we use a Beta Match, Cirquit Q, Delta match, Direct? Gamma match? Hairpin match, Omega match, Pi network, RLC network, L-C network,S-P Transmatch, Stub match, T-Match, or Transmatch?
Get out them calculators.. A little hint, this array would work almost like stacking yagis at a 1/4 wavelength apart. Another hint....by construction, does it look circular polarized? Does it resemble a poor mans parabolic? It's certainly not Helix either....but could it work like one?
Or.... ::) is it a photo shop toy and has no means of functional operation at all. You decide :o
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When using a magnetic mount antenna on a car, how do you get the cable from the antenna inside the car to the radio without deforming (crushing) the coax?
Note to Kathy & Jeff - don't tell me to leave the window or the door open. ;D
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When using a magnetic mount antenna on a car, how do you get the cable from the antenna inside the car to the radio without deforming (crushing) the coax?
Note to Kathy & Jeff - don't tell me to leave the window or the door open. ;D
This is definately the disavantage of a Magnetic Antenna. While the coax will get squished a little, the weather seal of the door usually provides enough room that the coaxial can handle it and won't be permanently damaged, though I'm sure Clint will inform us that it definately has an effect on the performance.
BTW, if you leave the coax in place for a long time your weather stripping gets "deformed" as well making it susceptible to leaking. But then "it NEVER rains in Southern California".
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Thanks Robert. The biggest problem I'm having with my radio is a wife that says, "You are NOT drilling a hole in my car!!!" >:( ;D
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Thanks Robert. The biggest problem I'm having with my radio is a wife that says, "You are NOT drilling a hole in my car!!!" >:( ;D
I think we're married to the same lady! MY wife says that.
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When I used a mag mount I was fortunate that the manufaturer had left a hole (plugged with a rubber plug) in the body under the trunk lid. I ran the cord through the plug and did not have a problem. The cord ran in the space between the the trunk lid and body to the mag mount.
My wife did not want an antenna on the car but after it was mounted she found it was real easy to find the car in a crowded parking lot. That might work with people that are a little reluctant.
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Must be an X-chromosome deal, I'm the same way. HOWEVER, there are other acceptable solutions.
When I had my Celica, I used a lip mount antenna in the middle of edge joining the rear window (some people mount them on the side lip). Had a great Diamond antenna on it and could easily open the lid without banging paint with the antenna. It has nylon pads to keep the paint safe, and since it doesn't move, I think there's less issue with scratches from dirt/dust than the mag mount. It comes with a cap if you want to take/leave off the antenna. Not all are made equal, I'll try to find mine to share the model and then you can compare. I really liked this solution for a sedan/coupe car. I'll leave y'all to calculate the radiation into the passenger compartment through the glass for 2m-440, see what you think....
On my Jeep & currently on my Tacoma shell I use a window mount because I park in a structure at work. Mike says the Larson is the best, comes with the antenna. As you'd expect, not quite as good as a direct connection but only a short step down, works very well.
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explain to your wife that a mag mount vibrating around on the micro dust under the mount will do more damage to her car than a hole will. She will end up with a dull sanded spot on her roof which will be much bigger than an NMO mount.
And Bob is right. Deforming coax changes the impedance and can be very bad for your radio.
A trunk lip mount as Kerin suggested is an okay alternative, as is a through the glass. Although they receive poorly. Larsen makes the best one.
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Are there any easy-to-follow instructions to make a J-pole? I've looked online, but I can't seem to find anything relatively easy (for the non-electrician-type person).
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No matter what kind you build you will have to have tools and know how to solder. There were about ten built at our workshop yesterday some by folks who had never soldered before. There are lots of on line plans, many of them don't work. I can give you plans for the ones that I know do work.
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No matter what kind you build you will have to have tools and know how to solder. There were about ten built at our workshop yesterday some by folks who had never soldered before. There are lots of on line plans, many of them don't work. I can give you plans for the ones that I know do work.
Clint,
Please email me the plans for those you know do work.
Thanks!
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Soldering - I guess I don't have the right tools. Bummer I couldn't make the workshop - I got bombarded with work on Sunday. Where can I purchase a J-pole? We'd like to put it in the tree over our house.
No matter what kind you build you will have to have tools and know how to solder. There were about ten built at our workshop yesterday some by folks who had never soldered before. There are lots of on line plans, many of them don't work. I can give you plans for the ones that I know do work.
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Here it is RobertW:
http://www.wrightwoodcalif.com/ham/ClintFoldableJPole.pdf
Or this graphic uses the same dimension for the 2 meter flexible jpole:
(http://www.wrightwoodcalif.com/ham/Jpolefig1.gif)
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Here's some conversation on the Palmdale guy as well as a posting from him...
Amateur Radio Creates Static in Community:
http://www.eham.net/articles/17401 (http://www.eham.net/articles/17401)
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There's some interesting comments in that link.
Thanks