Great post Rob, great discussion!
I'd love to hear more about the practicalities of routing open wire line
from feedpoint through heavily wooded lots, through house walls, etc etc,
to the shack.
73, Barry N1EU
On Tue, Oct 20, 2015 at 10:17 AM, Rob Atkinson <ranchorobbo@gmail.com>
wrote:
> >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
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