[TenTec] Open Wire Line - A CASE FOR OCFD

[Rob Atkinson]

>Perfect example. Another would be a full wave dipole. :)

A full wave center fed dipole will be voltage fed and have a Z of
around 5K ohms and put a vswr on the line of around 10:1.  The line
loss is negligible because it is a balanced line with an air
dielectric.  I will go up against a horizontal 1/2 wave balun and coax
fed dipole on 40 m. with my balanced line fed horizontal 1 wave center
fed dipole on 40 any day of the week and I will come out ahead across
40 m.   Both same height.

>
>But more generally, I'm talking about putting up a single dipole, whether center-fed or off-center fed, feeding it with open wire or window line, and loading it on all bands.
>

Brown, you are off in your own world of open wire line hating and you
are free to be irrational about it to your heart's content but you
occasionally pop up in some on-line forum somewhere and I see your
dis-information.  Perhaps you attempted the folly of feeding an
unbalanced (i.e. off center fed) dipole with balanced line as you
included it in your description above.   Surely you understand the
concept of unbalanced load fed with unbalanced line and balanced loads
fed with balanced line.  You don't feed an unbalanced load directly
with balanced line.

A high dipole 1/2 wave on the lowest frequency of interest and fed in
the center with decent open wire line with a characteristic impedance
of at least 600 ohms and matched with a correctly designed and
constructed truly balanced link coupled matching network, will run
rings around any coax fed dipole, especially on 80 meters where the
band is 500 kc wide.  You won't need a ridiculous ferrite core balun
at the feedpoint, sitting there adding to your losses with heat
reactance; you won't need a dozen dipoles to cover HF, and such a
system will deliver more power to the load on average on any HF
frequency than some hammy coax fed dipole will.   If any ham wants to
be obsessed with feeding a balanced load with an unbalanced line he is
free to do so and live in denial (I work everyone I hear blah blah)
but professionally designed and constructed shortwave broadcasting
plants always use balanced antennas and feed them with balanced line.
If they didn't work they wouldn't do it.

To be objective, there is one problem with a low band dipole used on
the high bands, and that is the pattern you wind up with.  An 80 m.
half wave dipole on 10 meters has many lobes going off in all
directions and even though the system in terms of power transfer is
efficient, the pattern is not reliable if the operator wants a good
idea of where is signal is going.  For that reason, I employ a second
dipole, 1/2 w. on 20 meters to cover the high bands.

73

Rob
K5UJ