Go Back   WorldwideDX Amateur Radio Forums > Citizens Band Related > CB Antennas


Amateur Callsign Lookup
Enter Callsign:

how effective is a j pole antenna on 11 meters ?

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 08-20-2010, 10:21 AM
BOOTY MONSTER
Guest
 
Posts: n/a
Default how effective is a j pole antenna on 11 meters ?


how effective is a j pole antenna compared to a 5/8wgp like a maco 5/8 ? how effective is it compared to a 5/8 vertical like a imax 2000 ? since it only has one ground element does the radiation pattern have a lobe or null to its sides ? going by the online calculators it would be a little under 26 feet tall on the cb band , but it would have a much smaller footprint due to not using/needing horizontal or sloped ground elements . it would even be a smaller footprint than a sigma 4 style , but of course bigger than a imax or the new sirio .

whats your thoughts , experiences or comments on the j pole antenna ?

J POLE ANTENNA DESIGN CALCULATOR by K4ABT



Reply With Quote
  #2  
Old 08-20-2010, 11:05 AM
Carl's Avatar
Technologicaly Challenged
iTrader: (9)
 
Join Date: May 2005
Posts: 887
Carl is on a distinguished road
Default

it would not work as well, there really only a 1/4 wave vertical dipole with a fancy stub to lower the impedance. if you want to build one go ahead, you would be better off building a cheap yagi.
__________________

NĜAAT

Reply With Quote
  #3  
Old 08-20-2010, 11:52 AM
Robb's Avatar
Yup
iTrader: (3)
 
Join Date: Dec 2008
Location: Silicon Valley CA, Storm Lake IA
Posts: 7,829
Robb is on a distinguished road
Default

Just as a guess; but the "A" dimension might make this impractical if are going to use copper for 11m. Isn't the Vector 4000 re-issue basically a J-pole? That design supports the upper vertical better than a 'simple' J-pole. What do you think - BootyMon? If using aluminum; then the velocity factor is different and the lengths must also change...
__________________
BASE: Kenwood TS-2000, GAP Titan DX, Diamond X50A, Sirio SY27-4, and IMAX 2000.
MOBILE: Galaxy DX99V w/RF Limited CR-577 mic, Sirio Z-180. Yaesu FT-8800R & Diamond NR-770.

Reply With Quote
  #4  
Old 08-20-2010, 12:06 PM
Marconi's Avatar
Supporting Member
iTrader: (0)
 
Join Date: Oct 2005
Location: Houston & Corpus Christi
Posts: 3,875
Marconi is on a distinguished road
Default

BM, based on the idea presented, IMO the main problem with a J-pole for 11 meters is using 25' feet of vertical 1/2" copper. Seems to me there will be a severe lack of lateral support even using rigged tubing. The idea may work well for 2 to 6 meters and higher however.

Carl, can you show us a link where you get the idea a typical J-pole is only a 1/4 wave radiator?
__________________
Marconi's YouTube Channel
We're just lucky that Mother Nature doesn't require our antenna systems to be perfect in order to work our radio.

Reply With Quote
  #5  
Old 08-20-2010, 12:15 PM
BOOTY MONSTER
Guest
 
Posts: n/a
Default

i remember freecell being very adamant that the sigma 4 (and its copies) were not j poles and i think theres several comments in the sigma 4 threads saying the same thing . if i tried it i would use aluminium and copper (i think) for the materials . your velocity factor comment reminds me that i forgot to ask how to tune a j pole . is it tuned by element length or shield/hot location on the elements ..... or both ?

Reply With Quote
  #6  
Old 08-20-2010, 12:36 PM
Marconi's Avatar
Supporting Member
iTrader: (0)
 
Join Date: Oct 2005
Location: Houston & Corpus Christi
Posts: 3,875
Marconi is on a distinguished road
Default

Quote:
Originally Posted by BOOTY MONSTER View Post
i remember freecell being very adamant that the sigma 4 (and its copies) were not j poles and i think theres several comments in the sigma 4 threads saying the same thing . if i tried it i would use aluminium and copper (i think) for the materials . your velocity factor comment reminds me that i forgot to ask how to tune a j pole . is it tuned by element length or shield/hot location on the elements ..... or both ?
I've never built one BM, but Bob has. I would guess the best swr would be found by moving the coax pigtail up and down on the two lower 1/4 wave elements and if it was not resonant where you wish, then trim or add length to the 1/4 wave and re-tune. If that didn't work then try the same with the longer element. I have seen them designed with tunable tips that allowed for some adjustment without having to mess with cutting or adding length.

You might want to read up on what K6MHE published some years ago in an article titled "The J-Pole Revisited". It's on the Internet and he considered a balun and insulating the J-Pole from the mast in his work.

Have you put your antenna up yet?
__________________
Marconi's YouTube Channel
We're just lucky that Mother Nature doesn't require our antenna systems to be perfect in order to work our radio.

Reply With Quote
  #7  
Old 08-20-2010, 01:16 PM
Crotchety Old Bastard
iTrader: (0)
 
Join Date: Apr 2005
Location: Oklahoma
Posts: 6,800
W5LZ is on a distinguished road
Default

A 'J'-pole should work about like any other 1/2 wave antenna (that's what it is, a 1/2 wave). There are practical aspects that determine what sort of metal should be used for an antenna. Strength is one of the things that determines that. Doesn't make a huge difference if it's copper, aluminum, steel, cast iron, or gold.
got a 50 foot pole? Put that impedance matching 'stub' the right distance down from the top of that pole and feed it as with any 'J'-pole, and you got an antenna almost 25 feet high. Ought'a work just fine. With a little adjusting of the various lengths/distances, you can do the same thing with a tower, or flag pole, or water tower, or grain silo.
'J'-poles on HF are sort of large and impractical, but, they would work as well on HF as they do on VHF/UHF.
- 'Doc

Reply With Quote
  #8  
Old 08-20-2010, 01:18 PM
Captain Kilowatt's Avatar
Professional Amateur
iTrader: (1)
 
Join Date: Apr 2005
Location: Nova Scotia,Canada
Posts: 10,543
Captain Kilowatt is on a distinguished road
Default

Quote:
Originally Posted by Carl View Post
it would not work as well, there really only a 1/4 wave vertical dipole with a fancy stub to lower the impedance. if you want to build one go ahead, you would be better off building a cheap yagi.

A J-pole is not a 1/4 wave. It is a 1/2 wave fed thru a 1/4 wave stub at one end. The overall length of a J-pole is 3/4 wavelengths high. As for not needing a groundplane versus not benefiting from a groundplane, well that is a different matter. The J-pole would benefit from a groundplane just like any other vertical antenna but it does not require one to obtain a good match. The adjustable 1/4 wave stub takes care of that.
__________________
Marriage is like a deck of cards. In the beginning all you need is two hearts and a diamond. By the end you wish you had a club and a spade.

Reply With Quote
Reply

Bookmarks
Worldwide Radio Forum



Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Super C antenna...this is really neat Moleculo Amateur Radio Antennas 14 01-19-2014 02:04 PM
CB Radio - Antenna Basics: Part 2 Robb CB Antennas 0 01-06-2010 03:37 PM
Antenna Matcher for 10-12 meters? Robb Meters, Mics & Other Accessories 14 12-26-2008 10:09 AM


All times are GMT -7. The time now is 03:32 AM.


Powered by vBulletin®
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Search Engine Optimization by vBSEO 3.6.0
Worldwide Radio Forum