Mal, a balun can have more than one purpose, most commonly they are used
as you said to transform balanced to unbalanced or visa versa. They are
also used to transform impedances. These baluns can be voltage mode or
current mode. Current mode baluns are used to reduce common mode
currents. Some people like to change the name for a balun depending on
how it is used, un-un, bal-bal, etc. I usually don't do this. So long
as you know the function to be performed and select the right balun for
the function, that is what is important. A 1 to 1 current mode balun is
often called a choke.
A vertical with a good radial system fed with coax doesn't require a
balun (or choke) to reduce common mode currents because it is an
unbalanced antenna and so is the feedline. The radials remove the
common mode currents from the feedline, or at least reduce them enough
to be insignificant. It is sometimes possible to use a balun to provide
a better impedance match between the vertical and the feedline. (That
is why Zero Five recommends them.)
The amount of heat you get within a balun depends on the balun design.
Some are poor, some are very good. Sometimes baluns get used in places
where they are outside their design range, like connected to a full
wavelength dipole. In places where the impedances are very high (either
the real part or the reactive part) a balun can dissipate a significant
amount of heat. What happens to the heat? Well if the balun is well
insulated it just builds up inside the balun, and if there is enough,
the balun will burn up, probably melting things and shorting out.
Jerry, K4SAV
N7mal wrote:
>Jerry I have a real problem with some of these explanations. Unfortunately I
>know just enough about antenna stuff to be dangerous. The purpose of a balun
>is to transform an unbalanced something to a balanced something. The
>feedline feeding a vertical is unbalanced so we are 1/2 way there. A
>vertical however is an unbalanced antenna and in most cases more unbalanced
>than the feedline feeding it. Something has to give and it's usually in the
>form of heat. How does the balun deal with the heat? What happens to all
>these crazy impedances when heat, (a lot of heat), becomes a factor?
>73
>
>
>MAL
>N7MAL
>BULLHEAD CITY, AZ
>http://www.n7mal.com
>Everyone in the world is
>entitled to be burdened
>by my opinion
>
>----- Original Message -----
>From: K4SAV
>To: towertalk@contesting.com
>Sent: Thursday, May 15, 2008 4:42
>Subject: Re: [TowerTalk] The Vertical and the Balun
>
>
>Daniel, the balun on the Zero Five is used to reduce the loss incurred
>by the coax feedline because of the very high SWR of the antenna. It
>does reduce it some but not nearly enough.
>
>A balun is not necessary for a vertical antenna. What is necessary, is
>that the antenna be matched to the feedline close enough to make the
>losses acceptable. That is difficult to do with a single component,
>for all band operation, for a vertical consisting of a fixed length. If
>your feedline is very short and low loss coax is used, a tuner in the
>shack may provide acceptable coax losses.
>
>Another problem with a fixed length antenna is associated with the
>radiated pattern. When a vertical becomes longer than about 5/8
>wavelength, the main radiated lobe starts going up at a high angle that
>is not useful for communications on the high bands. So although it is
>possible to make a matching network that will match a long vertical, it
>won't work very well.
>
>With a good matching network (it will be different on each band) and a
>good radial system, your 65 ft vertical should work well on 80, 40, and
>30. It will also work OK (but not great) on 160. The radial system
>will be the determining factor on how well it performs on 160. For 20
>meters and up the antenna is too long and the performance will be poor.
>It will be easily beaten by a low dipole on those bands.
>
>Jerry, K4SAV
>
>K4SAV wrote:
>
>
>
>>I guess you weren't paying attention. I just answered that question 5
>>days ago.
>>http://lists.contesting.com/archives//html/Towertalk/2008-05/msg00115.html
>>
>>Daniel Hileman wrote:
>>
>>
>>
>>
>>
>>>Hi Everyone,
>>>
>>>I am here to learn, so I will ask the question. I have been thinking a LOT
>>>about building a full size 1/4 wave vert for 75m...I am going to go with
>>>the hygain aluminum mast since I have plenty of room to guy it well. I was
>>>originally thinking hard about the Zero Five, but it's only 43' and
>>>$200.00 more expensive. It said you could get 160m-10m with a 4:1 balun
>>>and radials and a tuner. So...my question is, what does the balun do
>>>exactly? Can I make the 65' work on 160-10m well without the balun or
>>>should I plan on putting one on my 65' vertical as well?? Will it work
>>>decent on 160m??
>>>
>>>Thanks,
>>>Daniel N9WX
>>>_________________________________________________________________
>>>
>>>
>>>
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