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What Balun to use 1:1 or 4:1 ?



 
 
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  #1  
Old January 3rd 04, 04:42 AM
VE3PMK
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Default What Balun to use 1:1 or 4:1 ?

So in as much as I realise the importance of using a balun when feeding
certain antennas, what factors determine what ratio is best suited to the
application? Is there a general rule?
(That is to say a long-wire is best fed with 'x:1' where a loop antenna is
fed with 'y:1'?)
I typically connect a center fed dipole is with a 1:1, but what
configuration calls for the 4:1, or even the 9:1 ??


(reply here please, it'll probably make an informative reading for most)

Thanks,
Pat

  #2  
Old January 3rd 04, 08:53 AM
Mike
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Hello,

Forget reading books! Look at the aerial being used and the feeder
connecting it to your radio. Calculate the difference in impedance. Simple
as that.

"VE3PMK" wrote in message
...
So in as much as I realise the importance of using a balun when feeding
certain antennas, what factors determine what ratio is best suited to the
application? Is there a general rule?
(That is to say a long-wire is best fed with 'x:1' where a loop antenna is
fed with 'y:1'?)
I typically connect a center fed dipole is with a 1:1, but what
configuration calls for the 4:1, or even the 9:1 ??


(reply here please, it'll probably make an informative reading for most)

Thanks,
Pat



  #3  
Old January 3rd 04, 05:38 PM
Cecil Moore
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Default

VE3PMK wrote:
I typically connect a center fed dipole is with a 1:1, but what
configuration calls for the 4:1, or even the 9:1 ??


Tongue-in-cheek mode on:
If you are matching 50 ohms to 50 ohms, use a 1:1
If you are matching 50 ohms to 200 ohms, use a 4:1
If you are matching 50 ohms to 450 ohms, use a 9:1
Tongue-in-cheek mode off:

Just trying to emphasize that one needs to know what impedance occurs
at both the balun input and balun output terminals. If one doesn't
know, a 1:1 choke (current balun) is about as good a choice as any.

The impedance transforming function of a balun involves differential
currents. The choking function of a balun involves common-mode currents.
The relationship between these two currents can be measured but is
usually unknown. For the majority of HF ham radio applications, e.g.
multi-band operation from one dipole, IMO, the choking impedance is
more important than any transforming action higher than 1:1.

An example of where a 6:1 balun might be chosen is a resonant folded
dipole fed with 300 ohm balanced line. The SWR on the feedline will
be low. The impedance seen at the balun output terminals will be
in the neighborhood of 300 ohms. 300/6 = 50 ohms.

The key to proper balun functioning is that the choking impedance
needs to be at least five times the impedance looking out from
the balun output terminals, preferably higher. In an antenna
system with reflections, the impedance seen at the balun output
terminals will never be the characteristic impedance of the
feedline. Unless the antenna is matched to the feedline at the
antenna, the transmitter end will not see the Z0 of the feedline.
--
73, Cecil http://www.qsl.net/w5dxp



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  #4  
Old January 3rd 04, 06:47 PM
K9SQG
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Pat,

It is hard to give more than just very general guidance because "it depends".
The impedance of the antenna on the fundamental frequency and multi-band
frequencies of use will be the main determining factors. Frequently a 4:1
balun is appropriate for multiband installations since the impedence will vary
quite widely. It will be a good match on some and poor on others.

Personally, I prefer to use open wire or ladder line for multiband antennas. A
link coupled or double balanced tuner in the shack does the impedence
transformation with little loss.

73s,

Evan
  #5  
Old January 4th 04, 05:37 PM
Tarmo Tammaru
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Default


"VE3PMK" wrote in message
...
what
configuration calls for the 4:1, or even the 9:1 ??


Pat,
A 4:1 balun would be used in antennas with a 200 Ohm impedance. Examples are
(some) beams with a Beta match, Log Periodics, and beams with multiple
driven elements. It would also give a reasonable match to a folded dipole.

Tam/WB2TT


  #6  
Old January 8th 04, 12:37 PM
nisse
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Default

4:1 folded dipole
9:1 windom antenna

and they are just examples...

VE3PMK wrote:

So in as much as I realise the importance of using a balun when feeding
certain antennas, what factors determine what ratio is best suited to the
application? Is there a general rule?
(That is to say a long-wire is best fed with 'x:1' where a loop antenna is
fed with 'y:1'?)
I typically connect a center fed dipole is with a 1:1, but what
configuration calls for the 4:1, or even the 9:1 ??

(reply here please, it'll probably make an informative reading for most)

Thanks,
Pat


 




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