The Carolina Windom.
A long wire antenna for
portable operation.
If you want a good argument on HF
antennas bring up the Carolina
Windom.
Craig Williams W6CAW
Goals
 An effective multi-band, antenna for portable
and emergency HF operations.
 Can work without an antenna tuner.
 Easy to construct and deploy.
 Can be used for local Near-Vertical Incident
Skywave (NVIS) or long hall
communications depending on frequency.
 Cheap!
But first - What is NVIS?
 Near-Vertical Incident Skywave (NVIS)
propagation is generally considered to be Flayer ionospheric reflection at angles of 7090 degrees. It is skywave propagation
without the usual skip zone. The purpose of
NVIS is to communicate locally and
regionally, out to a few hundred miles, with
moderate power, simple antennas, and no
skip zone. NVIS is typically used on 160,
80/75, 60, and 40-meter bands by Amateur
radio operators using relatively low
horizontal wire dipole antennas.
From: http://www.athensarc.org/nvis.asp
NVIS or ?
75-meter NVIS antenna at 20
feet high.
The -10db ray is at about 38
degrees.
The -20db ray is at about 20
degrees.
From: http://www.athensarc.org/nvis.asp
75-meter antenna at 125 feet
high (half-wave).
No longer NVIS, but now a
"skip" antenna, with most of the
power at about 42 degrees.
NVIS and the F-layer
Above shows two of the three mechanisms that combine to attenuate low-angle
daytime signals: (1) Compare the radiated power, which is about 2db below peak
at 70 degrees, with the 30 degree angle, which is down about 14db. (2) Compare
the distance the rays must travel through the absorptive D-Layer (twice) at
various angles: the 30 degree ray has about twice as much loss as a very high
angle ray. (3) Add the normal attenuation due to path length (not shown). These
three factors, plus a little loss in the troposphere, all combine to attenuate lowangle signals in the daytime. As the sun gets higher, D-layer ionization intensifies,
and the effective range decreases further.
From: http://www.athensarc.org/nvis.asp
What is a
Carolina
Windom?
I found this Radio Works
Windom as I was
putting this
presentation together.
$140.00!
www.radioworks.com/
ccwcover.html.
Now, lets make one for
considerably less.
The 4 to 1 Balun
Toroid is a T106-2, Wireman Part # 903
How to at: www.w5fc.org/files/how-to/QRP%20Expressions_version_1.pdf
Testing the Balun
A 200 Ohm resistor is
connected between the
balanced leads A1 and B2
to simulate the 200 Ohm
feed point of the antenna.
The 50 Ohm test device is
connected to the
unbalanced feed point.
VSWR should be 1.0 across
frequencies of interest.
4 to 1 built for light weight
The throw away putty knife Balun.
The material is easy to work with,
cheap, and should hold up well for
temporary use. I decided to add
terminals for easy of assembly and
future repair. The coax is attached
on the back side with the shield
soldered to the ground windings on
the balun and the coax center to
B2. B2 and A1 go to the wire. The
formula to compute the length of
the wire is the standard
468/frequency with the 4/1 Balun at
62.2% from one end.
The wire is Toughcoat 'Silky' 26
AWG, 19 strand 40% copper-clad
steel from the Wireman # 534
4 to 1 Balun Potted
Balun “potted” with liquid RTV.
Common Mode
On an 80 Meter Carolina
Windom the Current
Balun is placed around
22 feet down the
vertical feed line from
the feed point. Using
this 22 feet of common
mode as a radiating
element the antenna
pattern is filled in as
seen here.
Radiation Pattern
At the design frequency of
80M the OCF antenna will
have a similar pattern to a
center fed antenna.
At higher frequency
harmonics the OCF will
have gain and pronounced
lobes towards it’s long
end. The pattern in Fig. 4
is for a two wavelength
dipole. Keep this in mind
when “pointing” your OCF
antenna
From:
http://www.blacksparrowmedia.com/misc_files/
The%20OCF-dipole3col.pdf
Antenna Current distribution
Current distribution at
center, 90 degree, and
OCF fed, 60 degree,
feed points.
At 80M the center feed
point = 70 Ohms.
Above 80M it varies
between 70 and 3000
Ohms!
The OCF feed point is
around 300 Ohms at
80M through 10M. This
is the key to multi-band
operation with the Off
Center Fed (OCF)
antenna.
From:
http://www.blacksparrowmedia.com/
misc_files/The%20OCFdipole3col.pdf
Antenna Length and Balun Placement?
Overall length of the wire. Use the standard formula
of 468/ frequency in Mhz for the total length. I find
this is usually long which is a good thing. In
portable operation I fold back the ends to get a
better match for the current environment it finds
itself in. ( height, ground Xr, surroundings )
Balun placement. I have been using the figure of
62.2% from one end. On 80M this morning WM6Z
from Imperial says he moves his balun around till
he gets the best VSWR with his analyzer. Why
didn’t I think of that?
The Current Balun
The current balun is made from 7
clamp on torroids from the
Wireman, part # 916. The RG58
feed line is looped through the
torroids 3 times. My current
balun’s are somewhat a guess
from looking at many articles on
the internet.
You know they work when your
tuner tunes properly. When they
don't your tuner does a long
mad hunt and never seems to
settle in as the common mode
current is still on the feed line.
The Mast
33' fiberglass push up
pole from The Mast
Company.
www.tmastco.com
The pole is mounted in
an RV flagpole mount I
got at the Del Mar Fair.
Home Made Mast Mount
A home made version of
the tire mount. The flat
part was laying around
the barn. It could be
duplicated with
anything sturdy enough
not to flex. Attached to
the "tire holder" is a
hardware store pipe
flange. Screwed into
the flange is a piece of
pipe screwed to a
female plastic PVC
connector. Glued to the
PVC connector is a
length of PVC pipe to
drop the push up pole
into. Adjust your PVC
pipe sizes to
accommodate your
push up pole diameter.
Deployed
Measurements
VSWR and more for the finished 80M Carolina Windom
( Adjusted for the General phone upper portion of 75M )
F MHz
VSW Rs
3.8
1.7
71
3.9
1.4
41
7.175
2.4
20
7.3
2.5
20
14.35
2.7
31
Measured with an MFJ-269 antenna analyzer
160 Meter Windom
Measured with an MFJ-269 antenna analyzer
Questions ?
More details on this project, with links to sources, and other projects by W6CAW
can be found at:
www.craigwilliams.com/radio