56ww
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 Re: A simple 1:1 Choke Balun
Yep, choke baluns work efficent if its close to antenna, other wise coax warmer or/and resonate wrong way.
why not that method can works, but air coil is best because better Q. If rounded to mast whit or whitout plastictube it not be so good and it works like bad coil, and if rf is on jacket then it radiate to metal and the mast will be antenna. If all is right and coax give all rf to antenna and if its in correct resonance and give all signal away, then its no big deal to round coax to mast, but never can do 100% resonant sysytem, so something coming back and make coil warmer and radiate to mast. Magnet field change considerably if slide metal inside or near coil same do antenna and coax what radiate. so if no back radiations on coax, then rf stay inside coax and cant radiate out, but if any rf is on jacket, then it behave as good as any normal single wire coil .
So thats why choke coil works, its a coil like any others.
73'mike
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23/Sep/2009, 10:19 pm
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crimso
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Re: A simple 1:1 Choke Balun
I'm not changing the subject here, so bear with me.
To make a simple & cheap QRP ATU, take an old broken transistor radio, remove the MW ferrite rod antenna & unwind the windings carefully, then take a piece of card & form a tube around the ferrite & re wind the wire windings from the antenna onto the tube, remove a capacitor...It has to be of a certain minimum pf, but any size above that will do & then make your in & out coax connections.
Now comes the relevance to the antenna mast inside of the ugly balun former. you tune this ATU by sliding the ferrite in & out of the former, just the simple act of moving the ferrite inside of the former with the windings on it, adjusts the impedence.
In the same way placing a conductive substance inside an ugly balan former would alter it's impedence & thus alter the impedence seen by both the radio & the antenna from what was 50 Ohm Coax.
Also don't forget the choke effect is achived by the resonence achived by the length of the coax in air,placing a former inside the air wound former would make it more broad band yes, but it would also allow RF, if you have any on your Coax to transfer to your mast during the windings around the mast prior to them becoming an RF choke at the frequency you are operating at.
What I am saying is that, if your RFI problem is due to RF transferring to the mast, than a RF choke wound around the mast would achive nothing but an alteration in SWR.
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24/Sep/2009, 6:50 am
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FB220
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Re: A simple 1:1 Choke Balun
You can see the one in the pictures on my website.
It works well !
--- My personal website and soon to be blog
http://www.wix.com/26fb220/26fb220 |
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20/Nov/2009, 9:55 pm
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