Helical wound antenna
Atsushi Otsuka
I have seen a couple of helical wound antenna projects for HF on the
published magazines and handbooks. They usually provide information
such as winding pitch and the length of the pole. But they don't
mention the total length of the wire nor the theory behind it.
Can you enlighten me about
(1) What is the total length of the element wire wound on the pole?
(2) How do you explain the operation of the antenna? Is it the same
as the 1/4 wavelength vertical antenna?
(3) Why do you need to wind the element? What is the advantage of
winding the element?
Thanks,
Atsushi Otsuka
7K2COJ
W8JI Tom
In article <52g4o2$d...@akebono.jpn.hp.com>, atsushi...@om.jpn.hp.com
(Atsushi Otsuka) writes:
>(1) What is the total length of the element wire wound on the pole?
Wire length is dependent on the distributed inductance and capacitance in
the element, and will vary greatly with winding pitch, wire size,
dielectric near the wire, and the antenna length. There is no exact rule.
The smallest length wire would be used if the winding was concentrated
near the feepoint, the longest length if winding pitch is concentrated
near the outer end.
>(2) How do you explain the operation of the antenna?
It is a simple loaded antenna, but it uses a very poor coil spread out
over a large area.
It has lower radiation resistance, more loss, and can have less bandwidth
than better designed systems.
>Is it the same as the 1/4 wavelength vertical antenna?
The helical antenna is less efficient and has lower radiation resistance,
so in that resspect it is different.
>(3) Why do you need to wind the element?
Because if the antenna is too short physically series inductance, end
capacitance, or a combination of the two is needed to make the antenna
resonant. Winding the element adds distributed series inductance.
>What is the advantage of winding the element?
Mutual coupling increases the inductance per unit length of space, and
that gives "free" inductance without having extra wire length. A longer
wire, required for the same reactance without mutual inductance, has more
resistive loss and lowers efficiency.
That's why proper shaped coils are so efficient for loading. Helical
antennas, as a general rule, are among the least efficient of all designs.
Radiation occurs because of charge acceleration over spacial distance, so
the wire length wound up is totally unimportant to radiation fields. Only
the length from tip to tip is important. For maximum radiation make the
physical length as long as possible with the least resistance (shortest
wire) in between, and concentrate loading at the high voltage end of the
element.
73 Tom
Richard Dunmyer
atsushi...@om.jpn.hp.com (Atsushi Otsuka) wrote:
>I have seen a couple of helical wound antenna projects for HF on the
>published magazines and handbooks. They usually provide information
>such as winding pitch and the length of the pole. But they don't
>mention the total length of the wire nor the theory behind it.
>Can you enlighten me about
>(1) What is the total length of the element wire wound on the pole?
>(2) How do you explain the operation of the antenna? Is it the same
> as the 1/4 wavelength vertical antenna?
>(3) Why do you need to wind the element? What is the advantage of
> winding the element?
>Thanks,
>Atsushi Otsuka
>7K2COJ
Well it has been a long time, but if I recall correctly the helical
vertical is actually a 1/2 wavelength of wire wound in a coil over a
fixed length....The ARRL antenna book has a couple of columns on this
type of antenna....The length of the pole it is wound on is not
terribly critical as I recall although the longer you can make it the
better....40 meter length of the pole was supposed to be about 7 feet
minimum...it is operated as a quarter wavelength and the SWR points
are pretty narrow as I recall...
A very very long time ago, in an ancient radio magazine which I cannot
recall whether it was QST or not, there was a design that some guy
made and used it inside his house...it was wound on lathe material and
had 1/2 wave wound on lathe which was about 1/4 inch thick and 2
inches wide, and about 15 inches long...he wound it for 15 meters and
he also wound 4 radials in the same manner....it worked ok....but then
I don't recall the year and it may have been a sunspot high back
then...
Illigitimi non carborundum
KD1YV
Richard Dunmyer wrote:
>
> atsushi...@om.jpn.hp.com (Atsushi Otsuka) wrote:
>
> >I have seen a couple of helical wound antenna projects for HF on the
> >published magazines and handbooks. They usually provide information
{snip}
Just as a side issue, perhaps interesting, perhaps not ...
One of the antenna vendors at the Boxboro hamfest this weekend had, on display, a
"40 meter rubber duck." It was about the size and shape of an inverted 2 liter
soda-pop bottle. I asked him if it worked, and he claimed that it did :-)
--
73 de Jim, KD1YV
Roy Lewallen
In article <32586B...@ix.netcom.com>,
Of course it does. "Worked" isn't a quantitative measure and can mean
anything the vendor would like it to. It'll radiate, sure. Its field
strength will be _many_ dB below a dipole, also sure. If you run a T
connector to your dummy load and attach a wire about the same length as the
40 meter "rubber ducky", it'll radiate just about the same as the "rubber
ducky" and will provide about as good an impedance match. On this I'll be
willing to bet real money.
Roy Lewallen, W7EL
Karl B. Staddon
I've used a helical wound dipole suspended from the fibreglass canopy of
my truck for several years with considerable success.
To make it, I wound a half wave length of solid copy wire on a broom
handle for EACH side of the dipole (that's right, double what you would
use for a regular dipole). I then tranfered the coiled wire onto a
string which in turn was suspended from the inside of the canopy by
creating 4 inch diameter loops with zap straps which I taped to the roof
with duct tape (subsequently replaced with 3M fibreglass filament tape -
it doesn't seem to unstick in the heat as bad as the duct tape).
The feedpoint is over the top of the hinge for the rear window of the
canopy. The legs of the dipole run parallel to the hinge until they
reach the side of the canopy and then they turn at right angles and run
all the way to the front of the canopy on each side. You have to fiddle
with the length to fine tune the resonant point. On balance it is not as
good a vertical mounted on the top of the truck, BUT you don't have to
put it up and take it down when going into a garage or under trees.
I've worked Indonesia, Russia, Sweden, Argentina, Peru and all over North
America with it and 100 watts.
Good luck, de Karl VE6KBS