balun ?

[arkieguide]

On my yagi 3 element beam, direct connect, what Balun should I use. 1 -1? Voltage are current ? Also
recommend a filter to keep from splattering around on TV's & radio's.Thanks guys, I all ways appreciate your views and idea's.

Thanks
arkieguide

 

[prcguy]

When you say "direct connect", are both driven elements insulated and floating from the boom or is one grounded? Or is it gamma match or T match or what?

On my yagi 3 element beam, direct connect, what Balun should I use. 1 -1? Voltage are current ? Also
recommend a filter to keep from splattering around on TV's & radio's.Thanks guys, I all ways appreciate your views and idea's.

Thanks
arkieguide

 

[arkieguide]

both driven elements are isolated from each other, and from the boom. Tye reflector and director are mounted to the boom.

 

[prcguy]

Thanks for the info. My favorite way to feed an insulated/isolated dipole in a Yagi is with a hairpin loop and 1:1 choke balun. The dipole impedance at resonance will be well below 50 ohms because of the close proximity to the other elements. A hairpin loop will match that lower impedance and a good 1:1 choke balun will isolate that dipole from the coax and the rest of the world.

I am on travel but could send you some pics of my hairpin loop matching on a couple of CB/10m Yagis I have in about 2 weeks. Basically you connect a good 1:1 choke balun right at the driven elements, then make a loop of maybe 12ga wire about 18" long overall and as wide as the gap between the elements at the feed point. I would measure the SWR with just the coax connected through the balun to start with.

Then connect the hairpin loop across the feed point and run the loop parallel but a few inches away from the boom. Check the match then trim an inch off the loop and repeat until you get a perfect match. My loops end up about a foot long and the length is not that critical. My Yagis use CB whips with 3/8-24 threads at the feedpoint so my hairpin loop is made from 3/4" flat stock and I drilled 3/8" holes at the end so when the whips screw in they hold the loop in place.

For a really good 1:1 choke balun for CB, get an FT-240-52 ferrite core and wrap 8 turns of RG-58 or RG-8X or RG-142 coax through it. That will probably handle a kW. For higher power stack two cores.

both driven elements are isolated from each other, and from the boom. Tye reflector and director are mounted to the boom.

 

[arkieguide]

I sure could use a picture please.
Thanks

 

[prcguy]

I won't be home for 2 weeks to get a picture but here is a similar project with a picture of a hairpin match on a 10m yagi. HF-antenna CW 10 meter 3 element YAGI-UDA - by ON4BAI - i1wqrlinkradio.com

I sure could use a picture please.
Thanks

 

[arkieguide]

Reply

I looked at the site you gave me, It is what i though, it is a jumper between the 2 isolated driven elements.I do thank you.
arkieguide

 

[prcguy]

You can see the approximate size of the hairpin in the picture, so start yours longer, maybe 18-20" and keep cutting it shorter until the match gets better then starts going back up. Then make a new one the length that gave the best match. The length is not super critical and an inch or two longer or shorter may not show much change.

For your balun, go to the second diagram down in this link and wrap the coax exactly like it shows around an FT-240-52 core. You will need 9 turns total and each time the coax passes through the center is considered one turn. You can buy the core here for $15: http://www.amidoncorp.com/ft-240-52/

This type of 1:1 choke balun will give a good 30dB isolation between the input and output over about 25 to 30MHz where others like a bunch of small beads over the coax will max out at about 20dB isolation.

I looked at the site you gave me, It is what i though, it is a jumper between the 2 isolated driven elements.I do thank you.
arkieguide

 

[arkieguide]

reply - choke balun

Thanks again - I will keep that information.

 

[JayMojave]

Yeah what PRCGUY said: I use the FT-240K torrid cores for my use. Maybe not a lot of difference as PRCGUY call out, but this is what Amidon uses in there 1 to 1 Current Baluns.

FT-240-K - Amidon

I needed a 1 to 1 current Balun for a CB dipole antenna, and used two of these cores epoxied together and used the good 10 Gauge Thermaleze coated wire that is bullet proof, at 9 turns of two wires, two input two output. This also worked great for a 20 meter dipole antenna.

Jay in the Great Mojave Desert

 

[prcguy]

If you wrap the two FT-240 size cores with RG-142/BU Teflon coax you will have a 1:1 choke balun that will take an easy 5kW. For high power using parallel wires you would want to cover the entire length of wires with Teflon tubing, otherwise you can easily exceed the voltage breakdown of the enamel insulation.

Wrapping the cores with coax will also be a consistent 50 ohms through the balun where parallel wires can't achieve 50 ohms even with the wires twisted. In this case the six or eight feet of wire wrapped around the cores will land somewhere around 70 to 100 ohms as the characteristic impedance of the balun.

Yeah what PRCGUY said: I use the FT-240K torrid cores for my use. Maybe not a lot of difference as PRCGUY call out, but this is what Amidon uses in there 1 to 1 Current Baluns.

FT-240-K - Amidon

I needed a 1 to 1 current Balun for a CB dipole antenna, and used two of these cores epoxied together and used the good 10 Gauge Thermaleze coated wire that is bullet proof, at 9 turns of two wires, two input two output. This also worked great for a 20 meter dipole antenna.

Jay in the Great Mojave Desert

 

[arkieguide]

Jay Mohave - thanks - more good information.