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Author Topic: Ladder Line  (Read 1297 times)
K5YF
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Posts: 77




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« Reply #15 on: November 18, 2008, 11:58:37 AM »

N4GMG de N5JYK,

Andrew (Andy?),
Commercial ladder line that is insulated is much easier to use than open ladder line. I haven't calculated it out, but there shouldn't be much difference in loss between insulated ladder line and open line (very low for balanced line regardless). I am assuming you are using the insulated type..

Ladder line isn't quite so sensitive to coupling as one might think, just as coax isn't impervious to coupling. As others have said, and conventional wizdom demands, keep it twice as far from a large parallel metal object as the wires of the ladder line are from each other. Crossing any metal object that is less than 1.5 times the width of the ladder line at anything near 90 degrees, will cause you no problems even if it is very close to it, even touching one that is thin and relatively short compared to the operating frequencies of the ladder line will usually not cause you problems.

All that said, read on: The greater the RF power any ladder line is carrying, the greater the magnetic coupling potential to nearby objects because the magnetic field is both stronger (flux is more dense) and larger (flux covers greater area) in response to that greater power (physics is funny that way). In other words at power levels of 10 watts or less, the insulated types of ladder line can lay directly on parallel non-energized conductors with pretty much no effect. If you notice no changes in impedance or stray rf characteristics between qrp and qro (in a proper installation there should be no change) your installation is good! Stray RF in this instance would be unintended currents induced in conductors other than the antenna elements -- like wiring, plumbing, and metal ducting. Besides, it is impossible to have a "perfect" installation. But its fun to strive for "best under the circumstances."

HAVE FUN!

W5DXP de N5JYK

Cecil, where do you get the plexiglass you use? I need a better source!

Have a great one guys!!!

-Brandon

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W5DXP
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Posts: 3613


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« Reply #16 on: November 18, 2008, 12:51:16 PM »

> W5DXP de N5JYK: Cecil, where do you get the plexiglass you use? I need a better source!

The piece that fits my window was bought more than 10 years ago in the Phoenix area. There was a plastics manufacturing company just off the interstate in South Phoenix. I was always buying their scrap material for some project.

I believe that Lowe's, Home Depot, etc. carry plexiglas. I need a piece for my new QTH and will run over there right now.
--
73, Cecil, w5dxp.com
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
WB3ERE
Member

Posts: 118




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« Reply #17 on: November 18, 2008, 01:54:34 PM »


Buy plexiglass...you must be kidding, I just drive over to the nearest glass store and ask if they have any plexiglass scrap that I can have.  They want to know what I'm going to use it for... antenna insulators I say, I'm a ham radio operator and love playing with wire antennas and the plexiglass makes nice insulators.  Usually they walk in back and come out with an arm load of scrap, I thank them and carry out my goodies.  Some get pitched in the trash once I get home because they're too small to be of use the rest gets set aside for "playing".

Try it, the worst they can say is "Get outta here kid", and think geeze don't these hams ever grow up. Wink

73 Ed
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N2UM
Member

Posts: 12




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« Reply #18 on: November 19, 2008, 06:07:56 PM »

I bring my ladderline through the storm and interior window.  I use split 1/2" foam pipe insulation both on the edge of the window and on the frame.  It gives separation between the ladderline and contact with metal window frame.  An added benefit of the foam insulator is that it fills the gap to keep drafts out.  I place a wood dowel in the window frame to lock the window.  I've used 600, 450 and 300 ohm ladderline/twinlead with great success using this method.

Good luck!
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