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Author Topic: Adding a balun to a Murch?  (Read 1745 times)
W9WD
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Posts: 9




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« on: January 10, 2013, 08:23:33 AM »

Anyone added a balun to their Murch UT-2000 tuner for the purpose of direct connection to a balanced line?

Greg

 Huh
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WB2WIK
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Posts: 20547




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« Reply #1 on: January 10, 2013, 09:14:41 AM »

I don't have one, but it should work.  The UT-2000 was based on W1ICP's article, "The Ultimate Transmatch" and is a T-match with differential input capacitor.

An external balun should work fine, as long as the balun itself is up to the task.
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W9WD
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Posts: 9




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« Reply #2 on: January 10, 2013, 09:21:53 AM »

Yep, I could do an external balun and that would surely be easier, but then I wouldn't get to fiddle around on the inside...

 Smiley
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WB6BYU
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Posts: 13039




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« Reply #3 on: January 10, 2013, 12:58:03 PM »

The circuit as used in most other tuners is simple enough.  For example, MFJ
adds a pair of terminals on the back panel for the balun and one for a "single
wire".  Because they use a 4 : 1 voltage balun, the single wire terminal is
jumpered to one of the balun output terminals to enable it.  If you don't want
to add a "single wire" terminal, connect a wire to one of the balun terminals
with a banana plug on the other end and plug it into the center of the output
connector when you want to use balanced line.  That way the balun winding
isn't connected in the circuit when you are using the tuner for other loads.

The "Ultimate Transmatch" design isn't as efficient as a standard T tuner when
matching low impedance loads, so a 1 : 1 current balun is probably a better
choice than a 4 : 1 voltage balun.  In that case, one of the output terminals
is NOT in common with the input, so you'll need a third terminal on the back of
the tuner if you want to plug it into the output to enable it, or a short coax
jumper sticking out the back with a plug on it.
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W9WD
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Posts: 9




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« Reply #4 on: January 10, 2013, 01:04:35 PM »

Or a switch?
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WB6BYU
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Posts: 13039




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« Reply #5 on: January 10, 2013, 02:18:36 PM »

You can add a switch, and it will need to withstand the highest output voltage
of the tuner.

Does the Murch have a build-tin antenna switch already?  I don't remember that it
does, but it has been a while since I looked at one up close and personal.  If so
you could wire the balun to one switch position.  If not, then you could install
one to choose either the coax output or the balun, which makes it a bit more
versatile, but it probably needs to be ceramic with wide spaced contacts to
handle the possible voltage (potential potential?) when matching wild loads.

Or perhaps a big knife switch on the top of the cabinet?
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KE3WD
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Posts: 5694




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« Reply #6 on: January 10, 2013, 03:41:00 PM »

Banana jacks on the back panel have always worked nice for me, avoiding the problems that switch might encounter when internal voltages get up there.  Spacing the jacks properly, such that a bipin jack can be turned into a shorting link works well, too. 


73
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KG6YV
Member

Posts: 506




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« Reply #7 on: January 10, 2013, 05:41:21 PM »

1.  Make sure ther is room for a balun. 
2.  If you use any switches be aware that voltages can be very high on the output side of any tuner.  I wouldn't try a toggle switch as they are not made to handle RF.  Now you are talking about a rotary ceramic switch which will require additional space in the box.  Those 2000's are not too spacious as I remember.

Gud Luck

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