Re: NEC-LIST:Terminated folded dipoles

Good day all.

As I recall, this is similar to one of the early simple wideband antennas used for
ionosondes. I do not have the copy to hand, but my memory suggests that it may be
in one of the IGY handbooks on ionospheric measurements dated around 1957. Allon,
as a matter of ineterest, do you still have the original manual at the Physics
Dept? The original ionosonde at the Physics Department, Rhodes University,
Grahamstown, South Africa used exactly this type of antenna strung between the
Physics Department and the clock tower. I seem to recall the feedline was driven
directly from two output valves/tubes in push-pull arrangement.

Best regards,
Duncan.

chris Turner wrote:

> I have been experimenting with terminated folded dipoles for some years now
> using various dimensions and terminations. I found impirically that a folded
> dipole roughly 40% lambda at the lowest operating frequency terminated with
> about 1000 ohms and fed with 16:1 balun from a 50 ohm source gave me a VSWR of
> less than 2:1 over a range from the lowest frequency to 30MHz.
>
> Efficiences reported by NEC-2 range from 12% to 40% depending on frequency.
> Radiation patterns are as one would expect from a doublet of the same length.
>
> I have experimented with all the so called critical dimensions in length and
> spacing and found that they were not really critical at all. Recently I have
> simulated all sorts of dimensions, in various configurations from flat tops to
> slopers and inverted Vees, and can honestly say that it is a most forgiving
> antenna. I have looked at the designs of W3HH and patent of Elmer Bush and
> find that their dimensions need not be duplicated to get satisfactory
> performance. In general signals are about 3 to 6dB below a resonant dipole at
> the same height on all the HF amateur bands.
>
> Does anyone have any experience and am I missing something here? I would be
> pleased to provide source files to anyone who wants to experiment.
>
> PS. The July Edition of Radcom (the RSGB journal) carries a short summary of
> some of the background.
>
> Chris Turner
> G4HKP/ZS6GM
> --
> The NEC-List mailing list <nec-list_at_gweep.ca>
> http://www.gweep.ca/mailman/listinfo.cgi/nec-list

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