Home made balums ? 4:1 - Canadian TV, Computing and Home Theatre Forums

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post #1 of 20 (permalink) Old 2017-12-27, 06:42 PM Thread Starter
 
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Home made balums ? 4:1

Built my first 4:1 balum today.
Out of coax cable 2 feet long . Made a air coil one . Using the gray 1/2 inside diameter electrical conduit.
Works great my tv power meter jumped form 35 to 44 on my vhf. And the uhf from 40 to 55-60.
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post #2 of 20 (permalink) Old 2017-12-28, 03:22 AM
 
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What balun did you use before?
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post #3 of 20 (permalink) Old 2017-12-28, 03:32 AM
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You mean "Signal Quality Percentage" and on what TV???

Not enough info to know what you built.....Air Core Coax Balun does not compute......

Antenna Simulations, Overload Calculations, etc: http://imageevent.com/holl_ands
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post #4 of 20 (permalink) Old 2018-01-23, 06:50 PM Thread Starter
 
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Sorry about that holl_ands , yes signal quality percentage, hisense tv
I took some 3/4 inch gray electrical piping , drill a hole in it, stuck 4 inches of the cable up and out then wrapped it four turns drilled another hole the stuck the cable up to match the other out put,
Then took my 15 foot test cable and stuffed it up the center.
Stripped the covering off not to cut the braided wire, on all 3 cable ends sticking out .
Tied all braided wires together ,
Then stripped off the copper wire cover and soldered one of the coil wrapped copper wires to the cable test length (15 foot section)
Then connected to antenna.

Turii it was a 4-1 balun that had an aluminum cover of 2 inches long with 3 caps tied in on the pcb board with the 4-1 wire setup not sure what company made it

Last edited by wildwillie; 2018-01-23 at 10:50 PM. Reason: Forgot some thing
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post #5 of 20 (permalink) Old 2018-01-23, 07:52 PM Thread Starter
 
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post #6 of 20 (permalink) Old 2018-01-23, 08:04 PM Thread Starter
 
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post #7 of 20 (permalink) Old 2018-01-23, 09:59 PM
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Thanks for the interesting photos, but can you show us an electrical wiring diagram for the balun so that we can see what is connected to what?

Please use the correct name for the 4:1 matching transformer.

It is called a BALUN, which is short for BALanced to UNbalanced. The 300 ohm connection is the balanced side because neither conductor is grounded. The 75 ohm connection is the unbalanced side because one conductor is grounded.

Only a neophyte calls it a balum, and you obviously have more experience than that. Your design shows considerable signal improvement.

http://www.eznec.com/Amateur/Articles/Baluns.pdf

https://www.google.com/search?biw=91....0.u4lrO4CoKKA

https://www.google.com/search?biw=91....0.9cyUBFjAZ0w

If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 2018-01-23 at 10:32 PM.
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post #8 of 20 (permalink) Old 2018-01-23, 10:09 PM Thread Starter
 
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OK rabbit73 lol sorry about that. It's in the hand book. I will see if can locate it
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post #9 of 20 (permalink) Old 2018-01-23, 10:35 PM Thread Starter
 
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First test rabbit73 was with a piece of coax cut for 585 MHz I lost my vhf stations , so I cut the next for a vhf of 2 feet , which worked well so I decided to coil it around a 3/4 inch piece of electrical conduit. Drill a hole big enough so coax will go threw , then feed 4 inches in that out the top . Coil it around 4 turns drill another hole push coax in an up threw. The push the feed coax threw . Then connect all shielding together , then the copper wiring as in picture
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post #10 of 20 (permalink) Old 2018-01-23, 10:48 PM
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Thank you for the diagram. That is a 4:1 halfwave coaxial balun which has a low loss.

It has a narrow bandwidth, so you can use it only for one TV band, either VHF-High or UHF, but not both. It must be cut to the proper length for each band as you found out.

A conventional ferrite core balun is needed to cover VHF and UHF, but it has a little more loss than a halfwave coaxial balun.

In post #2 Yurii asked you what balun were you using before the improvement?

If you can not measure it, you can not improve it.
Lord Kelvin, 1883
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post #11 of 20 (permalink) Old 2018-01-23, 10:53 PM Thread Starter
 
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When cut to the right length can be used for both test test test
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post #12 of 20 (permalink) Old 2018-01-23, 11:07 PM Thread Starter
 
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Rabbit73 it was a OT 1121 matching transformer ,
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post #13 of 20 (permalink) Old 2018-01-26, 02:36 AM
 
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What would the measurements be for a UHF coax based Balun?
And,
how do you join it, with the inner wire and outer metal sheaf?
Sincerely,
Schoolbus
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post #14 of 20 (permalink) Old 2018-01-26, 08:56 PM Thread Starter
 
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Schoolbus in post number 9
R2 is your antenna
Very carefully strip off the outer coating , I use a utility. Knife and cut along the coating to the outer end cut there I press a little deeper with the cut , then use my finger nail to start it to split.
The I pull the coating back .
Now the protective shielding I un twist it a bit to it nice and loose and pull it back.
If the centre wire has a foil wrapping around it I pull it back and cut it off,
Then strip the covering off the centre wire feed.
You need to strip 3 ends.
All outer shielding is connected together.
Look at pic in post 9 it shows you how to wire it up.
With a velocity factor of 0.66
Short loop measurements as so

470 MHz 8.287 inches
531 MHz 7.335 inches
585 MHz 6.658 inches
600 MHz 6.492 inches
174 MHz 22.385 inches
210 MHz 18.547 inches

You may have to test different lenghts to find the correct length that works for you DIY test test test
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post #15 of 20 (permalink) Old 2018-01-28, 04:55 AM
 
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Hello,
Does it matter how long the connections are in between coax parts, and coax to cable?
Also,
When you connect (to shielding too) is this soldered?

Schoobus
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