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Rob_Usa
| | Posted on Sunday, February 02, 2003 - 4:24 pm: | 
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My home-made J-pole for 11 meters out-performed my Imax 2000 locally. Even though the Imax was higher in the air, by 15 feet at the base, signal strength at 5-40 miles was better with the J-pole by an average of 1 S-unit. Receive was also better with the J-pole. Was built of 3/4" copper tubing with 1/2" used for the top section of the long vertical. Don't know if this was an isolated occourence or what. I feel more tests need to be ran. Any comments, suggestions, etc? |
Marconi
| | Posted on Sunday, February 02, 2003 - 5:23 pm: |
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Tell us more Rob. Maybe you could describe and give us how you tune. I am looking for something simple to go into a pine tree and I don't think these need any ground plane, rigth?
Marconi |
de
| | Posted on Sunday, February 02, 2003 - 6:54 pm: |
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Please correct me if I am in error as to the specs of the 2000. I seem to remember that one being a 5/8 wave vertical.
If you made a true traditional J pole, then congrats for doing so because to do so you would need three one quarter wave lengths in order to do so. That would mean you used at least a 30 foot telescopic pole to as your main radiator. Probably a 40 foot if you wanted to elevate it above ground.
Your findings of a better antenna in the J pole is due largly because the J Pole in its traditional configuration is longer and has a little more gain than the shorter 5/8 wave antenna. In addition to transmitting better you probably noted that your receive was better as well.
DE |
de
| | Posted on Sunday, February 02, 2003 - 6:59 pm: |
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Re Marconi....
Try here. Look on the bottom of the web site. Plug in the frequency (in Mhz of course) and get the dimensions required.
http://www.packetradio.com/jpol.htm
de |
Rob_Usa
| | Posted on Sunday, February 02, 2003 - 7:07 pm: |
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Actually tuned up very easy, although it's very tall - almost 26 feet. If set in a tree, which you said above that you would like to do, it should work great. Will be easy to support the taller section. The tree will be practically invisible at these frequencies. And yes, your right - no ground plane needed. I would suggest a ground-wire at the base for static and lightning protection. However, you can run a WHOLE LOT of power to these, and can't hurt them. Used standard hardware-store 3/4" rigid copper with a 1/2" rigid copper section at the top of the tall element. All joints were soldered - even the feedpoint when I got a match I was happy with. Now cover 26.4 - 28.7 under 2.0 to 1 SWR.
As far as dimensions, I simply used the formula(s) listed at the website below:
http://www.sedan.org/jpol.htm
Did have to trim a little off the ends, but it was just something to experiment with anyway. I had no idea it would perform so well. No wonder hams have used them for years. I wonder why these never caught on in the 11-meter band?
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bruce
| | Posted on Sunday, February 02, 2003 - 10:18 pm: |
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J-Poles do work well ive used them from 10 up to 3/4 meters i think the reason they are not popular is there is little money in them for a manufacture .... too easy to build! |
bullet
| | Posted on Monday, February 03, 2003 - 11:53 am: |
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rob,
ive been interested in building one of these j poles or the super j pole and have looked at those web sites as well. i wondered how they would compare to a i max 2000.
i run a pair of antron99's set up in a colinear
fashion and thus far it exceeds any thing ive ever run to date to include the 5/8th wave antennas.
i wonder how the j pole would perform set up like i have my antrons? have to be better id think! and lastly the super jpole configured as a coliner array if you could keep it up would have to be better yet!
bruce/marconi/rob,
what are your thoughts on these! |
bruce
| | Posted on Tuesday, February 04, 2003 - 5:13 am: |
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J-Poles are good antennas and work well but as for ver a 5/8 wave endfeed i dont think you would see much diffrence either way |
Rob_Usa
| | Posted on Tuesday, February 04, 2003 - 10:44 am: |
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Actually, i've seen J-poles co-linear in a 2 meter setup. Don't know how well they worked, but it should work great for CB too. Just wish I still had my old MACO V to compare this thing to. |
Rob_Usa
| | Posted on Tuesday, February 04, 2003 - 10:54 am: |
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Hope I don't offend any fans of the Imax. I just started this thread because I thought it was interesting that a home-made $30.00 hardware-store antenna outperformed my factory made antenna, which claims to be one of the best. And, of course, to get the feedback of others. I've been playing with antenna designs for a couple of years now - looking for the most efficient vertical and have had trouble beating the J-pole's performance. It was just an experiment - something to have fun with. After all, the weakest link of any radio system is usually the antenna. |
bruce
| | Posted on Tuesday, February 04, 2003 - 1:32 pm: |
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ROB nothing beats saying I MADE IT IT WORKS GREAT! |
Alsworld
| | Posted on Tuesday, February 04, 2003 - 2:30 pm: |
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Rob Usa,
I'm an IMAX Owner and took no offense. I think it's quite interesting and applaud your success. Sounds like a fun project to try, especially with your positive results.
I wonder about TVI pro's or con's? Tech833? Bruce? I'm just curious if a copper J-Pole would be better than the fiberglass antennas, or if it's more in the radio setup. I am intrigued.
Alsworld |
Kb5lpa
| | Posted on Wednesday, February 05, 2003 - 1:52 pm: |
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A good antenna will make a marginal radio sound good. A poor antenna will make the best radio sound like 2 cans with a piece of string tied between them.
A J pole is a good antenna. Have a guy in our talk around group that built one for 10 meters. Rather long but really did a great job. The downside was cost of copper, and weight. My A-99 did just as well when we had a dx station come in. He was in Australia. Our signal reports were the same(57) however his audio was a bit higher than mine. He has a really new radio and mine is 12 years old. We are about 1&1/2 miles apart so the path was pretty close. He still threatens to put it up. His wife decided it needed to come down due to "grandson ground waves"!
73 de KB5LPA |
Phineas
| | Posted on Wednesday, February 05, 2003 - 2:55 pm: |
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Well, you would gain many things from a jpole over an end fed.
1. Bandwidth. Mainly due to the size of the conductor.
2. More gain cause there is no coil in te bottom of it.
3. Durability. Even though we are talking about a pretty heavy antenna.
4. Reduced TVI because there is no "Coil".
5. Power Handling is not an issue.
6. J-Poles work vertical and horizontal.
7. Work great as driven elements for Yagis
Downsides.
1. The antenna is definitely heavier.
2. Due to being broad banded, you are going to have more intermod problems.
3. Also due to band width, you recieve will not be as good.
Frankly, I am glad to see more CBers getting into building antennas. If more people did that, they would find out that it would greatly decrease the amount of power they need. It would also put some of these CB rip off companies to shame.
Phineas |
Tech833
| | Posted on Wednesday, February 05, 2003 - 10:31 pm: |
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TVI is not a product of antenna design. TVI is normally generated in the transmitter. However, TVI can be generated in the antenna or feedline if there are loose connections or arcing.
People have a strange idea of what TVI is and what causes it. Drop the voodoo explanations and apply theory to it and the problem becomes quite simple to understand and simple to solve. |
Phineas
| | Posted on Thursday, February 06, 2003 - 8:20 am: |
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Tech833
Are you trying to say that a coil in an antenna cannot, and does not cause TVI?
HUH
Phineas |
Rob_Usa
| | Posted on Thursday, February 06, 2003 - 11:13 am: |
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Phineas, you're right. There are a few rip-offs in the CB world, but that's a topic for another thread. My next j-pole will be made from aluminum tubing, but that will be a while. For directional use, my next project will be a Half-Square. But, that's a month or two away and another great antenna that's been overlooked in the CB world |
bullet
| | Posted on Thursday, February 06, 2003 - 12:35 pm: |
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bruce,rob,others
i wonder if you know the optimum spacing for two antennas in a colinear array?
ive seen these with very little spacing and have read that its spacing is not real critical.
is this so, or is it the same as co-phaseing antennas side by side as regards to spacing.
ive mounted the top antron99 at 66ft at the feed point the lower one at 36ft to feed point and 9ft out from the tower. they have about 12ft spacing between them.this seems to work quite well but i have really not tried other spacings to improve performance as yet.
im having some slight tvi with this set up due to coupling of the 75 ohm coax near the lower antenna i believe.
i plan to wind the coax at the feedpoints of both antennas, and add a groundplain kit to them to help in this matter. but spacing will have to be shortened so i can get the extra coax to wind for the 1:1 baluns.
this system although not quite right yet is talking 50-65 "airmiles" on 4 watts carrier at nite when its quiet,i do this every nite. a single antron99 at this location is getting 30-35 airmiles at 4 watts carrier. |
Tech833
| | Posted on Thursday, February 06, 2003 - 10:04 pm: |
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Phineas: "Are you trying to say that a coil in an antenna cannot, and does not cause TVI? "
That is what I am saying. A coil itself will not cause TVI, that is impossible. A coil with loose connections that arc (microscopically or otherwise) or a radio with harmonics will cause TVI. |
DE
| | Posted on Thursday, February 06, 2003 - 11:45 pm: |
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I must agree with 833....
A coil and or cap in series or parallel only makes your radio think it is seeing a longer or shorter piece of wire.
If your signal radiated manages to penetrate the faulty shielding of a cable junction box the fault should be laid where it belongs. On the faulty box not the RF which merely found the entrance.
The problem with most televisons today is that they are made with little or no shielding. The manufacturers would much rather not spend the couple of bucks per unit rather than put in built in high pass filter. |
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