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Author Topic: Help on 10 meter dipole  (Read 295 times)
KB1PDG
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Posts: 27




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« on: June 16, 2008, 05:09:36 AM »

I built a 10 meter dipole and i'm feeding it with 300ohm twin lead to my dentron super tuner. can match the antenna and rig very well but the performance is poor compared to a coax fed vertical imax 2000. is this due to loss from the twin lead? any suggestions would help. thanks.
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W4DRR
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Posts: 82




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« Reply #1 on: June 16, 2008, 05:43:01 AM »

Here is a novel idea...
feed it with coax and lose the tuner.  Works everytime.

73,
Bob
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73,
Bob
KB1GTX
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Posts: 462




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« Reply #2 on: June 16, 2008, 05:48:18 AM »

IS the dipole horizontal and the other vertical?
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N3OX
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« Reply #3 on: June 16, 2008, 06:14:59 AM »

How high is the dipole?  How is it oriented compared to the stations you're working?  Is the twin lead routed to the shack clear of other metallic and/or poorly dielectric objects (dirt, trees?)

Also, who are you working?  You're talking about working band openings and not locals with verticals, right?  

W4DRR's impulse to replace with coax makes some sense to me too  if you want to use this as a single band dipole (mostly for convenience and simplicity), but at the same time, a dipole cut somewhere in the vicinity of 10m fed with 300 ohm twinlead and a decent tuner should work fine on 10m.

If it's low, maybe the Imax beats it.  If it's high and oriented 90 degrees from the stations the band is open to, I'd expect the Imax to beat it too.  And at random times otherwise, I'd expect them to be neck and neck.  But if you get the dipole up good and high, I would expect it to be better on average than the vertical.

73,
Dan



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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
WA3SKN
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Posts: 5497




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« Reply #4 on: June 16, 2008, 06:37:32 AM »

I doubt its line loss.
You are probably comparing the low angle radiation of the vertical to the higher angle radiation of a low mounted horizontal dipole.  Try mounting the dipole vertically and see if you are still hearing the same differences!
73s.

-Mike.
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G8UBJ
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Posts: 478


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« Reply #5 on: June 16, 2008, 06:40:43 AM »

How long is this dipole, have you built a dipole for the 10M band not a 10M long dipole?

If its for the 10M band (28.5 mhz) it should be 8.21' each side

http://www.hamuniverse.com/dipivcal.html

if you feed it directly with coax create a coaxial balun with 10 turns of coax at the feedpoint.

If you feed it using ladder line take it all the way your tuner which needs to include a balanced output?

http://www.sdarc.net/m0xuk/new_posts_front.jpg

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WB2WIK
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Posts: 20612




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« Reply #6 on: June 16, 2008, 06:10:47 PM »

For a monoband dipole (10m only), no reason to use twin lead or the tuner.  Feed with coax and a balun, and you'll eliminate the tuner loss, which can be substantial depending upon how long the twin lead is.

Or, you can cut the twin lead to a precise length to make it match the dipole perfectly with almost no "tuning:"   That would be 15-1/2' or any interval of 15-1/2' long: 31', or 46-1/2', or 62', etc.  With that precise length, the twin lead will appear electrically to be the same as coax.

No reason to use twin lead for a single band resonant antenna -- it usually just complicates the situation because under some conditions, you could be trying to match a very serious mismatch with the tuner, introducing tuner losses you won't have with the vertical.

A 10m dipole should be 16-1/2 feet long, end to end.

WB2WIK/6
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