balun

[mc-20]

trying to get a little more out of this KX1 , I found a site on baluns, is
anyone else listening in to the eham.net. there is comment on the balun
pages  that says there is no real good balun for low power,  my question is
why not, is it not the purpose to keep everything in balance to get the best
out of your antenna no matter the power. the eham site does not offer any
explanations on this but one HAM operator says DXE balms claim to fame is
high power out puts.

mike
kb7dpc


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[Vic K2VCO]

mc wrote:

> there is comment on the
> balun pages  that says there is no real good balun for low power,  my
> question is why not, is it not the purpose to keep everything in balance
> to get the best out of your antenna no matter the power. the eham site
> does not offer any explanations on this but one HAM operator says DXE
> balms claim to fame is high power out puts.

If the balun is inefficient, the loss will be the same in DB at QRP or
QRO.  If the balun has a loss of, say 3 DB, then it will make your KW
sound like 500 watts and your 5 watts sound like 2.5.

Having said that, power loss is power converted to heat, so you might
not notice a lossy balun when operating QRP; at QRO it would heat and
possibly burn up.

Finally, a balun may be more or less effective at reducing common mode
currents (that is, converting between balanced/unbalanced), apart from
losses.  And one balun may have a wider frequency range in which it is
efficient and effective than another.

So there is definitely a sense in which one balun is better than
another, even for QRP.

--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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[Charles Greene-2]

Mike,

The reason is that for small 4:1 baluns, you need more turns of wire
on them to get the necessary inductance,  more turns means a smaller
wire to fit, and a smaller wire means the impedance of the two wire
transmission line is not optimum for a 4:1 balun.  You will have a
high SWR just due to the balun.  However, I have made many small 1:1
baluns using several turns of RG-174 on a toroidal core, by placing
ferrite beads (12 FB43-801 beads work nicely) on the outside of a
piece of RG-174, or just winding a bifilar pair of #22 enamel
insulated magnetic wire on a toroidal core.  You need a F114-43 or a
F140-43 core to get enough impedance for 80 meters, although a
smaller core will work for 40 up.  Palomar sells a BA-58 bead kit for
RG-58.  Actually, a 1:1 balun works as well on a random length
transmission line as a 4:1 balun.  Unless the load is a predictable
200 ohms or there about like you get on an OCF antenna, the impedance
of an open wire feed line is just as likely to be near than 50 ohms
as it is near 200 ohms.   You also can use a Low Power balun for 100
watts like the Elecraft balun kit, or the one on the NJQRP web site.

DXE baluns are for high power, are large and heavy, and cost a lot of money.

73,  Chas W1CG

At 06:04 PM 10/11/2005, mc wrote:

>trying to get a little more out of this KX1 , I found a site on
>baluns, is anyone else listening in to the eham.net. there is
>comment on the balun pages  that says there is no real good balun
>for low power,  my question is why not, is it not the purpose to
>keep everything in balance to get the best out of your antenna no
>matter the power. the eham site does not offer any explanations on
>this but one HAM operator says DXE balms claim to fame is high power out puts.
>
>mike
>kb7dpc
>
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[Martin Gillen]

Hi, Mike.

I routinely feed a 66ft dipole with 300 ohm TV
twinlead
by hooking it directly to the KX1 using a BNC to
binding
post converter.

The KX1 ATU seems to match this quite nicely.

The antenna performance seems to be very good.

I have a BLT tuner on order;  when I get it built I
will compare how the antenna performs with/without a
balun.

Martin.


               
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