[Elecraft] Baluns and 450 ohm line

[Don Wilhelm]

Stuart and all,

I use a 124 foot antenna center fed with 450 ohm line.  At one time I ran
the 450 ohm line all the way to the shack - 45 feet of it.  When I measured
the impedance at the line input I found most bands were in the vicinity of
100 ohms impedance.  OK this is a compromise between a 1:1 balun and a 1:4
balun, so I constructed both ratios of current baluns and tried them out.
If I used the 4:1 balun, I found the impedance the tuner had to deal with
was quite low and with the normal T network tuner, that is the area where
the potentila losses are greatest.
I settled for t\using the 1:1 balun and found that I could tune the antenna
system quite nicely without concern for losses in the tuner.

Just one thing more to consider.  There is NO reason to believe that just
because you have 450 ohm ladder line attached to the antenna that the
feedpoint impedance will be anywhere near 450 ohms - it can be quite low on
several bands and is highly dependent on the feedline length.

73,
Don Wilhelm  - Wake Forest, NC   W3FPR home page: http://www.qsl.net/w3fpr/
  QRP-L # 485   K2  SN 0020   mailto: w3fpr@arrl.net

*** Life is what happens when you're making other plans -- Mike Cross  ***

----- Original Message ----- >
> Actually at QRP levels, the usual unbalanced T tuner with balun on its
> output works multiband just fine feeding a 450 ohm line with a 4:1 balun
as
> is built into all the common commercial T matchers.  We placed in top 10
of
> field day with such a set up over past 7 years.  If you get some band with
a
> sensitivity to the length of 450 ohm feeder you are using, add 5 or 10
feet
> and retune.  True, we do not worry what impedance the line is seeing, just
> that it be in the range of the transmatch plus line we use.  ... snip