Folklore dies hard.
At a recent ham convention some clown brought his
helically loaded loop and put it on display. He
proudly held court and explained to anyone
who would listen about how great it was. I
bet my 4 inch Hi-Q screwdriver with CB whip
on top could beat that loop in a shoot out.
Rick N6RK
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On 12/6/2014 1:48 AM, qrp.gaijin@... [loopantennas] wrote:
In loopantennas@..., <richard@...> wrote :
> It has been experimentally verified countless times that helically
> loaded verticals have no special properties compared to conventional
loading coils. Why should it be different with loops?
The detrimental effect on efficiency of helical winding of a small loop
has finally been verified in practice by K4HKX with experimental data
measured using the Reverse Beacon Network and carefully controlling for
environmental parameters. The result: helical winding introduces loss,
about 1-2 dB with K4HKX's loop, compared to a non-helically-wound loop
of equivalent enclosed area. W8JI already pointed this out more than
thre! e years ago when the helically-wound loop was first proposed.
Quote by W8JI: "Regretfully, all helcially winding the small loop does
is increase inductance and loss resistance. It is of no benefit at all
for radiation." (Reference: )
The measured objective data showing this conclusion can be seen here:
(see "Section 3: Magloop Comparisons vs My
Reference 40M Dipole:" and "Section 9: Helically Wound Magloop".
Simply winding the strap non-helically around the support frame would
improve efficiency (see for example K4HKX's aluminum strap loop) by
reducing the current path length and the loss resistance.
!
Best regards,
qrp.gaijin@...
---In loopantennas@..., <richard@...> wrote :
On 8/30/2014 6:12 AM, jwin95@... <mailto:jwin95@...> [loopantennas] wrote:
> Rick, since I have seen differences between 'real life' and what
NEC-2
> based MOM modelers yield regarding loop antennas, I don't have quite the
> 'faith' you do in their infallibility. Were it not for the fact that a
> helical loop is not a simple planar (2-space) structure but occupies a
> non-trivial amount of volume in 3-space I would still like to see a
> basis-in-physics explanation outside of the reliance of the usual
> modeling programs.
It would be very easy to build a loop and put in lumped element
inductors to experimentally verify that magic happens or doesn't happen.
But consider this thought experiment. If the loop radiation
resistance is only 0.013 ohms, any coils you insert with more than a few
dozen ohms of reactance add significant losses relative to 0.013 ohms.
But a few dozen ohms of reactance has negligible effect on anything. A
helically wound strap is not a free lunch. The total conductor path is
longer and narrower, hence increasing losses.
It has been experimentally verified countless times that helically
loaded verticals have no special properties compared to conventional
loading coils. Why should it be different with loops?
>
> Yet to be explained as well is the phenom where Ae > physical size as it
> may apply to loops.
What is it that hasn't been explained? Lots of antennas have
Ae > physical size. That doesn't mean that helically wound loops
have additional Ae. Where physical size comes into play is that
you cannot simultaneously have small physical size and high efficiency
without extremely narrow bandwidth and limited power handling due to
the necessarily high loaded Q. The proof of this is independent of how
the antenna is constructed. The article originally cited makes no
mention of bandwidth.
Rick N6RK
