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 Post subject: Junkbox 9:1 Balun (unun) for Receive ONLY
PostPosted: Nov Wed 10, 2010 3:49 am 
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Location: West Salem, OH
Here is a simple junk box balun you can create using an old television splitter, and some enameled wire.

Start with an old splitter from a tv, you know the kind that goes from 75 ohms and splits off to 300 ohm vhf, uhf, and fm. The one I used looked like this

http://antiqueradios.com/gallery/d/1274 ... litter.jpg

Carefully pry it open along the seams. Usually a small bladed screwdriver will work, once you have it in just a gentle twist and they usually pop open. Just take your time and when you are done you will see something like this

http://antiqueradios.com/gallery/v/temp ... 2.jpg.html

For the next step you will snip the two bare wires from the circuit board to the screw terminals so that the whole board may be removed

http://antiqueradios.com/gallery/v/temp/Balun1.JPG.html

Once you have the board removed take a pair of cutters and snap the board at the indicated lines. You won't be needing the other half and the ferrite balun needs the space where this was in the shell


http://antiqueradios.com/gallery/v/temp/Balun2.JPG.html

Position the board and connector so that the components (capacitors and inductors) are visible. Snip them all off as you won't be needing them as well

http://antiqueradios.com/gallery/v/temp/Balun3.JPG.html

For the next steps I do not have photos as of yet but will post. You will want to take your ferrite rod and measure it by laying it across the top of the case opposite the circuit board and connector. This is the space that was taken up by the now discarded portion of the circuit board.

I use discarded antenna rods from old junk radios. You can use either the round or the flat style. I prefer the flat for this kind of enclosure. Mark the length and using a file scribe a notch across the ferrite bar. I then put mine in a wooden vise right behind the notch. You can use any vise but use something like wood to protect the ferrite rod and don't over tighten! Carefully snap the rod to length.

Now take your enameled wire and wrap 30 turns closely spaced around the rod. This forms the primary of the transformer. Use tape to keep it in place leaving a few inches of lead sticking out the same direction. Now wrap the secondary which is 10 turns of the enameled wire. Try and keep them closely spaced as the ferrite rod is rather short due to the housing in use. I have wrapped turns of the secondary on top of the primary with no ill effects if it is larger diameter and there is insufficient room.

You can now either varnish, dip in wax, or just wrap good quality electrical tap around the wire covering it and keeping it in place. Be sure to leave a tiny gap for each of the four wires sticking out but otherwise cover the entire coil.

Once you have the coils secured to the form you must remove the enamel from the wires so they can be soldered. You can use a knife to scrape it off or a small piece of sandpaper works well too.

At this point it is ready to be placed into the housing. I like to use double sided tape. I find the automotive trim stuff works very well for this. Cut it the length of the ferrite rod and then stick it to the housing. Now press the rod onto it holding it into place. Make sure the leads are sticking out towards the connectors and the terminals as they will be connected next.

http://antiqueradios.com/gallery/v/temp/Balun5.JPG.html

Take one lead of each coil from the primary and secondary wrapping them around the lug for the screw terminal. Trim one short and leave the other long. Note the red arrow showing them both soldered to the terminal. The secondary is a bit hard to see but it is there. Now take the longest lead and place it on the circuit board where the shield side connects to the tv connector. You can see where it is soldered to the board to the left of the connector.

Take the opposite end wire from the primary coil and solder it to the screw terminal pointed to by the blue arrow. This leaves the last lead which is the secondary of the balun. Solder it to the circuit board as shown by the yellow arrow. This is right behind where the center terminal of the connector is also soldered.

At this point you are nearly complete. Put both halves together gluing them with something like super glue or other good plastic glue you have on hand. I also like to run a bead of RTV around the edge where the halves meet to seal it. Where the two cable came through the top I usually loop a heavy tie wrap through them and then seal with RTV as well. The tie wrap makes it handy to hang the balun from whatever support you have handy at the antenna.

When the balun is done it should look something like this

http://antiqueradios.com/gallery/v/temp/Balun6.jpg.html

The screw terminal denoted by "A" is of course for your wire antenna. This could be a long wire, gutter, or whatever you are attaching it to. The terminal marked "G" is of course for the ground connection. You want to make sure you have a decent ground as it is part of the secret to how this antenna works. The antenna will now always be at ground potential. This helps prevent any static buildup for one. Solid state radios will thank you for that! The longer the wire, the higher the electrical charge that can be had on the antenna. Especially in the cold winter months when the wind is blowing and it is snowing!

At this point I use catv coax line (75 ohm) to go to the radio from the balun. First it is cheap and plentiful. Second most of it is quad shielded and very low loss line. The slight mismatch of 75 ohms will be no problem for the radio. And the connector crimps right on easily. No messing with pl-259's at least on this end. Be sure and seal all of it well with RTV. The terminal screws will rust if you don't and you will want to seal the coax well too. Keep the water out! It is the enemy of antenna installations!

This balun will be especially useful in high noise areas as it will calm the noise down to a great degree. You might see a reduction in signal level however the noise will drop much more leaving far more signals to copy and enjoy!

I hope this help and I will fill in with some more photos as time permits. I did not have any ferrite material handy when doing this writeup but will fill in the blanks soon! Happy DXing and enjoy!!

[/img]

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Last edited by KB8CWB on Nov Wed 10, 2010 4:04 am, edited 1 time in total.

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 Post subject:
PostPosted: Nov Wed 10, 2010 3:54 am 
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Joined: Aug Mon 24, 2009 10:26 pm
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Location: West Salem, OH
I apologize as I could not get the images to insert properly. Seems either I don't understand how it is supposed to work or the links from the gallery hate me! I have them for now as links you must click on. I will update this as time permits and hopefully fix the issues. For now I hope it helps some out and if you have any questions pm me and I will be happy to help.

Bill

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PostPosted: Nov Wed 10, 2010 1:08 pm 
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Joined: Jan Mon 21, 2008 2:57 pm
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Location: VA
Bill, thanks a lot, it is very simple but the steps are clear and I seem to need this kind of help. Thanks again. John


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 Post subject:
PostPosted: Nov Wed 10, 2010 4:51 pm 
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Location: Crawfordsville, Indiana 47933
Great presentation. That way helps new guys see what they are doing. A lot of people need visible examples to better understand the text. I for one do as I get older.

Darn, I think I through all those old hookups out when I moved to the city and went on the worthless gazillion channel cable. :D :D

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 Post subject:
PostPosted: Dec Wed 22, 2010 5:52 pm 
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Location: La Porte, IN, USA
I like it.
Will it work on SW as well as BCB?

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 Post subject:
PostPosted: Jan Sun 30, 2011 6:36 pm 
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Joined: Aug Mon 24, 2009 10:26 pm
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Location: West Salem, OH
OZ132HOME said:
Quote:
Will it work on SW as well as BCB?


Yes sorry for the delay it works very well for the sw bands. It is what I primarily use it for however it is very good for mw as well. When I want better on mw I turn to the beverages... :wink:


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