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Author Topic: Balun Design Help  (Read 1038 times)
KI4NX
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Posts: 121




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« on: January 11, 2007, 08:32:25 AM »

I am trying to make a 1:1 high power balun. I constructed  the balun using T300A-2 toroid with #14 wire covered with a teflon sleeve. I used 12 turns with a crossover at the mid point to have the input opposite the output side. With a 50 ohm load, it get a 2:1 SWR one 160M and 3:1 on 80M. However, everything above 4.2MHz is off the scale. I wanted it to operate 160M thru 10M.  What am I doing wrong?
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N3OX
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« Reply #1 on: January 11, 2007, 10:22:31 AM »

Off the cuff, I wonder why you used a #2 powdered iron toroid.

I feel like you need ferrite for a wideband transformer.

Was the #2 material specified in a design, calculated, or did you just have it around?
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
N3OX
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« Reply #2 on: January 11, 2007, 10:23:14 AM »

nevermind... wireman kit or something, eh?
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
KB4QAA
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« Reply #3 on: January 11, 2007, 11:21:28 AM »

It's impossible to anwser without know what type of antenna you are using and it's dimensions, and what type of feedline you are using.

73, Bill
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KB4QAA
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« Reply #4 on: January 11, 2007, 11:24:46 AM »

Oops, on third reading, N3OX is right in his first post.  
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KI4NX
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Posts: 121




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« Reply #5 on: January 11, 2007, 11:39:46 AM »

I am hoping to use this with ladder line to an 80M dipole . I'm limited by HOA and stuff so height is the roof about 35 ft and antenna is folded at the corners of the roof. The toroid was part of a kit I got a few years ago  for with another antenna in another house with no HOA, so it was laying around and I made use of it.  
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KZ1X
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« Reply #6 on: January 11, 2007, 12:16:29 PM »

Seems like you're short about 5 or 6 turns ... just a SWAG.
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K0BG
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« Reply #7 on: January 11, 2007, 12:35:34 PM »

Yes, I wonder why a #2 as well. An F240-61 or -67 would be a better choice. In any case, it is all a little moot if the rest of the story isn't known.

Is there an antenna tuner being used?
What is the antenna?
Are you trying to wind a current or voltage balun?
What ratio?
Etc.?

Alan, KØBG
www.k0bg.com
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KI4NX
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Posts: 121




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« Reply #8 on: January 11, 2007, 12:50:31 PM »

Thanks for all the replies.

I am trying to construct a 1:1 current balun. I will be using a tuner with my antenna to get to use the other bands. I thought I could use the T300 with about 12 turns but maybe I need more turns on it. I will try that tonight.
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SSB
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« Reply #9 on: January 11, 2007, 02:41:41 PM »

What you need to realize is that the typical balun you are going to use is effective up to about 200 ohms.  Every day hams use these baluns up to thousands of ohms and wonder why things don't quite work well.  Hi Z baluns are wound on stacks of 5 to 10 cores of -43 material.

Alex....
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W5DXP
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« Reply #10 on: January 11, 2007, 04:50:15 PM »

The AL values for powdered-iron toroids are somewhat confusing compared to ferrite toroids. For instance, the AL value for T-300-2 is 115 uH/100T where the AL value for an FT-240-61 is 173 mH/1000T. See the difference? uH Vs mH and 100T Vs 1000T? Note that AL is proportional to N^2 and 100^2 = 10,000 while 1000^2 = 1,000,000.

IMO, the FT-240-K is the toroid to use and seems to have been designed for TLT applications. It's AL value is 4912 mH/1000T. Stacking two or three of them would make a formidable choke.
--
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.
WA1RNE
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« Reply #11 on: January 11, 2007, 06:34:50 PM »


 Whether the core is correct or not in order to behave as a common mode choke with enough impedance on 160 or 80 is one thing.

 
 But the winding itself - even without a core, i.e. wound on a plastic tube -or no core at all- should still behave as a 50 ohm transmission line if the wire size vs. spacing is correct for 50 ohms, so there should be negligible SWR.

 Something else is wrong. How exactly did you wind the balun?

 Did you reverse the winding direction when you made the crossover?  Any photos?


 WA1RNE
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KI4NX
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« Reply #12 on: January 12, 2007, 12:50:57 AM »

Thanks for all replies.

From all the comments, it appears the choice of T-300A is not right. Well, it was available. Maybe next time and lesson learnt, well, the hard way. I need that on occasion, so says my xyl.  

In answer a few questions, I did reverse the windings in the crossover and I will be ordering a couple of ferrite 240 cores from Amidon Assoc. I disassembled the windings so no pictures are available.

Again, thanks to all for your comments and help.

73
Ken, KZ4Y
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KI4NX
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« Reply #13 on: January 12, 2007, 06:08:16 AM »

Follow up.

I missed that small difference when I was looking at the charts, (milli vs micro). It's kind of obvious now and it sticks out like a sore thumb.  If I really want to put that iron powder core to use, I would need something like 30-33 turns.  What a difference! Just the same, I ordered Ft-240-K toroids this am - it would be lots easier to make with 10 turns vs 30 turns.

Once again, my thanks to all.
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SSB
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« Reply #14 on: January 12, 2007, 08:06:03 AM »

The Amidon K type toroid information on the Amidon site is incorrect.  I talked with Amidon a few months ago and they  know its wrong but they don't know the correct value.


Alex...
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