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Author Topic: Uses for a 4:1 voltage balun  (Read 596 times)
KG8JK
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Posts: 20




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« on: December 05, 2017, 03:04:00 AM »

Hello,
I picked up a 4:1 balun at Dayton last year and decided to give an OCF antenna a try. I put up an 80m  OCF and it works very well but I am getting some RF into the shack on 80m and a bit on 40m. After doing some research I learned (so at least I am learning something) that a current balun is much better for this application than a voltage balun. I am not looking to spend a bunch of money on this and would like to use the voltage balun that I have. What type of antenna would be better to use with the 4:1 voltage balun that I already have?  Would installing a ferite bead choke at the feedpoint help with the RF?

My goal is to have a multiband antenna with just one feedline going into the house (to keep the XYL happy).

Thanks
KG8JK
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W5DXP
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« Reply #1 on: December 05, 2017, 04:42:20 AM »

If you leave your antenna system as is and simply add a good 1:1 choke about 22 feet down from the feedpoint, you will have a Carolina Windom.

https://www.hamradiosecrets.com/image-files/windom-antenna.gif

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WB6BYU
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« Reply #2 on: December 05, 2017, 06:25:02 AM »

Adding an effective choke in the feedline or grounding the coax shield (for
example, via a lightning arrestor clamped to a ground rod), or a combination
of the two, may reduce your "RF-in-the-shack" problems. I would put the
choke at the feedpoint if possible, but other locations may work.


In my experience, large loop antennas seem to be less susceptible to
imbalance, and I often have used 4 : 1 voltage baluns for something like a
horizontal full wave loop.  If cut for about 3.55 MHz it should give a reasonable
SWR at some point on most HF bands.
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AE0Q
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« Reply #3 on: December 05, 2017, 06:52:25 AM »

If you leave your antenna system as is and simply add a good 1:1 choke about 22 feet down from the feedpoint, you will have a Carolina Windom.

https://www.hamradiosecrets.com/image-files/windom-antenna.gif


Here is the link to the whole page about the Carolina Windom:

https://www.hamradiosecrets.com/windom-antenna.html

I've used mine for contesting at portable locations with very good success.  The vertical component seems to work well.

Glenn AE0Q
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Glenn and V-NATCH Katie,
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http://www.hoopsandjumps.com/
http://funagility.webs.com/
N8CMQ
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Posts: 695




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« Reply #4 on: December 05, 2017, 07:11:47 AM »

Your antenna is an unbalanced design and any feedline is going to have common mode RF problems, as the feedline is in the RF field, and not at a neutral point.

For common mode voltage, a voltage balun or current balun is only going to work at the balance or neutral point of the antenna where the RF field is canceled out and does not cause the common mode current on the feedline.

That is why balanced dipoles and ground plane verticals became popular. But even the best design fails when the feedline is run parallel to the antenna rather than at a 90 degree angle from the antenna.

Adding ferrite beads to the feedline to choke the RF works to a point, and having them at both ends works better.

If you can run the coax underground for a long length works very well, as the earth losses choke any RF from the outside of the coax.

Another factor to consider is, your feedline, like any other conductor, can cause pattern distortion depending on where it is in the RF field even if you have chokes on the coax, having it in a neutral field point helps prevent that from happening.

Now, having a 4:1 voltage balun, you can build a folded dipole which has a characteristic impedance of 300 ohms, and use 75 ohm coax like RG-6 and have a very good antenna with a very low SWR, or use RG-400 with 50 ohms, and the SWR goes up just a tad, but is still very good. A 1:1 current balun can be used with a regular dipole with either 50 or 75 ohm coax with good SWR as well.

Neither antenna is going to be a "multiband" antenna like the OCF, but it will probably work better on the bands it is resonant on, and no tuner needed on the primary band it is designed for.

For a true multiband antenna, a nice ground mounted vertical, hidden as a flagpole if needed, may be what works better.
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N8CMQ   Jeff Retired...
KU3X
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Posts: 435




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« Reply #5 on: December 05, 2017, 08:05:38 AM »

Get hold of an FT 240-43 or an FT 240-31 ferrite core.

http://kitsandparts.com/toroids.php

Mouser.com also stocks these cores.

If you are using RG 213 coax, remove the PL 259 and wrape 8 turns through the ferrite core, next to your voltage balun. Install a PL 259 back on your coax and you are ready to go.

The so called Carolina Window ( which is not a windom at all !) is more hype than anything.

Barry
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VA3RR
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Posts: 28




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« Reply #6 on: December 05, 2017, 08:09:16 AM »

If you leave your antenna system as is and simply add a good 1:1 choke about 22 feet down from the feedpoint, you will have a Carolina Windom.

Agreed.  A 4:1 ruthroff followed by a 1:1 guanella is likely superior to a 4:1 guanella balun for OCF applications, the reason being is a 4:1 guanella does not have the same level of CM suppression as a 1:1 guanella current balun (or choke).
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KG8JK
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« Reply #7 on: December 05, 2017, 12:26:23 PM »

Thanks guys. That is all very helpful.

73

KG8JK
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