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Conference cvg::hamradio_iii

Title:Amateur Radio
Notice:Classifieds in #8, please register in #3
Moderator:CVG::EDRYM
Created:Wed Jun 15 1994
Last Modified:Fri Jun 06 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:504
Total number of notes:3678

495.0. "How to feed a W8JK array." by BIS6::VANDEWEYER () Fri Mar 14 1997 15:12

    I want to built a four element W8JK collinear antenna for 30 meter.
    However I'm not sure what's the best way to connect it to my
    tranceiver. I'm using a MFJ 9030 with an output of only 5 watts, so 
    I can't afford to lose something in the feeding line.
    
    Can I just use a 3 1/2 to 1 balun to transform the antennas impedance 
    (wich is I think 600 ohm) to 50 ohm. In the same time this should solve
    the balanced-unbalanced mismatch. 
    
    Anyone  who can tell me about his experience with this kind
    of antenna???
    
    
    				Regards, ON7KT Dirk Vandeweyer
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495.1do the match and balance at the same time..TEKVAX::KOPECConsider a spherical chicken; ..Mon Mar 17 1997 17:0911
    If you're really concerned about getting every watt to the antenna, I'd
    use twin-lead of some sort to feed the antenna, and build a
    link-coupled tuner with a balanced output link. Carefully constructed
    with air-core and air-dielectric parts, such a tuner can be very
    low-loss, and you deal with the matching and the balanced-unbalanced
    issued at the same time.
    
    Lots of ham handbooks have info on such things; I can scan something in
    if you don't have access to any..
    
    ...tom
495.2Twin line lossesBIS6::VANDEWEYERTue Mar 18 1997 13:486
    Thanks Tom for the reply.
    My intention was to use coax because of the better quality. Wont I lose
    to mutch power in the twin lead. I have to cover a distance of about 35
    meters.
    
    					Regards, Dirk.
495.3much less loss than coax..TEKVAX::KOPECConsider a spherical chicken; ..Thu Mar 20 1997 09:0615
    as long as you keep it away from the ground and conductive objects,
    parallel-line is very low loss.. especially when run with a high SWR
    (which you'll have, unless you do some matching at the antenna)
    
    I would probably use osmething better than TV twinlead if this is a
    permanent installation (I like the smaller window lead; 18ga stranded
    copper conductors, about half an inch spacing, black poly insulation)
    
    I've found that the wider window lead with solid copperweld conductors
    doesn't hold up well if it is subject to any flexing at all..
    
    ("window lead" is solid-dielectric parallel-conductor line with
    "windows" punched out of the dielectric)
    
    ...tom