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Message |
    
Joey_migs
Junior Member
Username: Joey_migs
Post Number: 15
Registered: 9-2009
| | Posted on Tuesday, September 15, 2009 - 10:39 am: | 
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I am currently constructing a J-Pole using type M copper pipe. I have read various articles and ARRL books on the J-pole and can't figure out how to feed it using 50 ohm coax - some say direct feed the center conductor to driven (radiator) element and the braided to 1/4 wave matching section , varying the placement up and down for minimum SWR. Other articles and books suggest the the use of a variable capacitor. Can anyone set me straight?
Thanks, in advance,
Joe |
Joey_migs
Junior Member
Username: Joey_migs
Post Number: 16
Registered: 9-2009
| | Posted on Tuesday, September 15, 2009 - 11:37 am: |
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BTW, I calculated the J-Pole dimensions for 11 Meters, if this makes a difference.
Migs |
Slugo4449
Intermediate Member
Username: Slugo4449
Post Number: 187
Registered: 7-2004
| | Posted on Tuesday, September 15, 2009 - 5:34 pm: |
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Joey:
Do an internet search for "j-pole calculator" There are a couple of sites that all you do is put the frequency in and it calculates all the lengths and also the placement of the feed point.
there are also many discussion about it on the net.
I have never seen one with a matching vari-cap attached. But, try it and see if it works!
Making antennas should be fun! |
Joey_migs
Junior Member
Username: Joey_migs
Post Number: 19
Registered: 9-2009
| | Posted on Tuesday, September 15, 2009 - 5:54 pm: |
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I agree. Making antennas should be fun. Mr Bill concurs.
One of the ARRL articles actually suggests using a copper disk slug (No pun intended) brazed onto a threaded rod tapped through the matching 1/4 wave section as to allow it to vary its distance from the radiator. Thanks for the response.
Joe |
Tech237
Moderator
Username: Tech237
Post Number: 1219
Registered: 4-2004
| | Posted on Wednesday, September 16, 2009 - 3:10 pm: |
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Never needed to use a capacitor on any J-pole I have built. I just use copper saddle clamps to hold the coax ends (via ring terminals, nut and bolts) and just slide the clamps up and down for adjustment.
Simon
Tech237
N7AUS
.
I thought he said, "there was no rust for the wicked, and I own an MGB"
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Allagator
Advanced Member
Username: Allagator
Post Number: 802
Registered: 9-2002
| | Posted on Thursday, November 26, 2009 - 12:03 pm: |
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make a 4 to 5 turn coil in the coax at the antenna to decouple the antenna then start to tune the swr in !!! |
Tech833
Moderator
Username: Tech833
Post Number: 1792
Registered: 8-2002
| | Posted on Friday, November 27, 2009 - 10:52 pm: |
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You should not need a current balun (turns of coax) on a J-pole.
Your radio 'Mythbuster' since 1998
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Press_man
Member
Username: Press_man
Post Number: 88
Registered: 5-2008
| | Posted on Thursday, December 03, 2009 - 11:38 am: |
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Made a bunch of J-poles for 2 mtr and never had an issue. These were 300 ohm flat wire inside of pvc pipe with so-239. Great little antenna. At mount points I'd cut the pipe and install a coupling or end cap then mount with doubled rubber lined cadnium coated clamps. Attach to a 4 piece pool pole and you've got 20' height. Or hall it up a tree on a rope.
Wally/Pressman/KC4ZWM
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