20m Halfwave Vertical QST article
 

QST had an article about a 20 meter halfwave vertical that was end fed with
a coaxial matching section for 50 ohm feed.
It was essentially a j-pole constructed from coax. It was in a 1980-early
1990 issue of QST. Does anyone recall the article
and the issue?

Thanks,

Mike N2MS

Sounds like "The Half-Wave Vertical" by John Belrose, VE2CV in September
1981 _Ham Radio_. It's a sleeve dipole, like the antenna I've heard
called a "bazooka" when used at VHF. That used to be a common type of
VHF/UHF antenna although I don't see many around these days.

Roy Lewallen, W7EL

Michael St. Angelo wrote:
QST had an article about a 20 meter halfwave vertical that was end fed with
a coaxial matching section for 50 ohm feed.
It was essentially a j-pole constructed from coax. It was in a 1980-early
1990 issue of QST. Does anyone recall the article
and the issue?

Thanks,

Mike N2MS

On Fri, 8 Jul 2005 22:17:43 -0400, Michael St. Angelo wrote:

QST had an article about a 20 meter halfwave vertical that was end fed with
a coaxial matching section for 50 ohm feed.
It was essentially a j-pole constructed from coax. It was in a 1980-early
1990 issue of QST. Does anyone recall the article
and the issue?

Thanks,

Mike N2MS

You have mail.

WWV uses half wave verticals that are center fed. Their web pages might
show the details. End feeding seems more difficult than center feeding.
73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Michael St. Angelo" wrote in message
...
QST had an article about a 20 meter halfwave vertical that was end fed
with
a coaxial matching section for 50 ohm feed.
It was essentially a j-pole constructed from coax. It was in a 1980-early
1990 issue of QST. Does anyone recall the article
and the issue?

Thanks,

Mike N2MS

"Michael St. Angelo" wrote in message
...
QST had an article about a 20 meter halfwave vertical that was end fed
with a coaxial matching section for 50 ohm feed.
It was essentially a j-pole constructed from coax. It was in a 1980-early
1990 issue of QST. Does anyone recall the article
and the issue?

Thanks,

Mike N2MS

Here is the NIST WWV web page that Mac, N8TT referenced !
http://tf.nist.gov/timefreq/stations/wwv.html
WWV Antennas

The WWV antennas are half-wave vertical antennas that radiate
omnidirectional patterns. There are actually 5 antennas at the station site,
one for each frequency. Each antenna is connected to a single transmitter
using a rigid coaxial line, and the site is designed so that no two coaxial
lines cross. Each antenna is mounted on a tower that is approximately one
half-wavelength tall. The tallest tower, for 2.5 MHz, is about 60 m tall.
The shortest tower, for 20 MHz, is about 7.5 m tall. The top half of each
antenna is a quarter-wavelength radiating element. The bottom half of each
antenna consists of 9 quarter-wavelength wires that connect to the center of
the tower and slope downwards to the ground at a 45 degree angle. This
sloping skirt functions as the lower half of the radiating system and also
guys the antenna.

====

Greg, w9gb

The bottom half of each
antenna consists of 9 quarter-wavelength wires that connect to the
center of
the tower and slope downwards to the ground at a 45 degree angle.

Sure, thats a "1/2 wave" antenna, but I would always consider that
a ground plane, rather than 1/2 wave vertical. It's got sloping
radials.
Same thing I used to run on 40m. I always called it a 1/4 wave ground
plane... MK

End feeding seems more difficult than center feeding.

Fairly easy. I always preferred the "gamma loop" type
matching device. On a low freq antenna, that loop could get a
bit large. On 20m, a 18-22 inch single turn loop would match it no
problem.
maybe less than that, cuz using the "standard" 22 inch loop for 20m,
you will usually tap around the mid point of the coil. So the coil
could
be shrunk down, to use more of it. I always used lengths of coax for
caps
if needed. "open stub" 100-120 pf is a good value for 20m.
You can also use a regular coil to match, but my gut feeling is the
single turn coil is a bit more efficient. I've never actually compared
though...
BTW...I consider WWV's antennas to be 1/4 wave ground planes being they
have elevated sloping 1/4 wave radials.
MK

When radials are in the same plane, they don't radiate a significant
amount. But when slanted downward, they do, pretty much the same as a
conical element of the same outside dimensions. You can call a quarter
wave vertical with sloping radials a "quarter wave ground plane" if you
like, but unlike one with horizontal radials, the radiating portion is
longer than a quarter wavelength.

In the case of the antenna being described, the upper radiating part of
the dipole is a quarter wavelength and the lower part is about 0.7 times
a quarter wavelength but effectively large diameter.

We have to get over the notion that calling some part of the antenna
structure "ground" gives it some kind of special properties. It doesn't.

Roy Lewallen, W7EL

wrote:
The bottom half of each
antenna consists of 9 quarter-wavelength wires that connect to the
center of
the tower and slope downwards to the ground at a 45 degree angle.

Sure, thats a "1/2 wave" antenna, but I would always consider that
a ground plane, rather than 1/2 wave vertical. It's got sloping
radials.
Same thing I used to run on 40m. I always called it a 1/4 wave ground
plane... MK

In article ,
Roy Lewallen wrote:

We have to get over the notion that calling some part of the antenna
structure "ground" gives it some kind of special properties. It doesn't.

I think it was Bob Pease of National Semiconductor who commented along
the lines of "You may be able to trust your mother. If you're
extremely lucky you may be able to trust your government. You can't
trust your ground."

Or, in the short form, "There is no ground". At least, not as a
single, uniform entity with constant (and special) properties.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

We have to get over the notion that calling some part of the antenna
structure "ground" gives it some kind of special properties. It
doesn't.


Never said it did. But I still consider it a ground plane... :/
Or at least more of a ground plane, than a straight 1/2 wave.
Note the "VHFGP" in eznec, or elnec. It's noted as a "ground plane"
and is almost exactly the same antenna as WWV's versions.
Same 45 degree slope with the radials.
I do agree about the rest though.
BTW, when comparing a model of a "flat radial" GP, and one with
sloped radials, there looks to be an increase of current from the
radials,
but it's not huge. I think you need to get a pretty steep angle going
for the
cancellation effects to really disappear. In comparing the two on 10m,
at
40 ft at the base, the difference in gain between the two is very
small.
About a 1/10 a db or so... Where I show the straight 1/2 wave to be
appx .6 to .7 db better than the 1/4 GP's. Sloped radials, or straight.

Tends to make me think the 45 degree sloped version still acts a bit
more
like a usual flat GP, than the straight 1/2 wave. I think if you get
to 20 degrees
or less, then yes, it starts thinking it's more a straight vertical.
Of course, in the real world you would probably be hard pressed to tell
a
difference between any of them. MK