Doug,
Nice write up.
Other Readers,
I'd like to make a comment about the antenna as I know more than
just a little about the things. An off center fed, OCF, dipole is not a
magic antenna as some hams have come to believe. They are just a good
wire antenna that is fed in a way to make them appear to have a 50 Ohm
impedance. They are based on the 1/2 wave dipole which only has a
workable impedance at 1/2 wave. At even multiples of a 1/2 wave, the
antenna exhibits a high impendance which most radios do not like. So,
way back in radio history a smart guy said if I don't feed the dipole in
the center I can find a spot that looks like 300 Ohms and use a
transformer to make it look like 50 Ohms over several bands. When he
invented that antenna, the only odd band was 15 meters. What that meant
was that if you created an 80 meter OCF dipole, you could use it on 40,
20, and 10 meters, without a tuner.
The basic 1/2 wave dipole antenna can be awesome if hung up at some
reasonable height. When fed in the center it is going to have a very
high SWR, which means you need to be careful of transmission line loss
and have some way to deal with the SWR. Open wire feeders handle the
loss issue and a very good tuner does the rest. Or you go to the OCF
dipole and use a 6:1 CURRENT balun or balun and line isolator.
When a dipole is operated at multiples of a 1/2 wave you can
actually develops gain in the plane of the antenna. How much gain and
lobe direction is a function of how many 1/2 waves the antenna is.
Those of you who want a good basic antenna and don't want to spent
a lot and can get it up about 30-35 feet or higher go for the OCF
dipole. I think you'll be happy. I have one up in my yard at about 40'
on one end and about 35 on the other( it has to do with the slope of the
land) and, as Doug, I work out everywhere. There are several sources for
the basic OCF antenna and a source for a variant that I run. However,
building one is a snap. Just go to Home Depot and buy 135' of #12
stranded insolated house wire ( color is unimportant ) have it cut such
that the cut is about a 1/3 of the way off an end. Pick up some
insulators at a hamfest and order either a 4:1 or 6:1 CURRENT balun.
feed the beast with some low loss or reasonable loss cable, and then sit
back and have fun. I would expect DXCC in 30 days, band conditions being
good.
Some final comments. I use #12 insulated, stranded wire just for
the extra strength. I don't want to be puting up a new antenna every
time we have high winds or ice. You could use #14 which most use, but
like I said I don't want to have to re-install my antenna. You will need
an antenna tuner, but that is OK as you will now be able to use the
antenna on all bands 80-10. Lastly, if you don't have 135' feed of
horizontal space you could bend the ends down to fit if it represents a
minor portion of the antenna Or you could build a 40 meter version using
66' of wire and just not work 80 effectively; I can actually get mine to
tune on 80, but it isn't great.
73,
Barry
K3NDM
On 1/11/2014 12:34 PM, Doug Ellmore Sr. wrote:
I saw some discussions on OCFS. I thought I would share my setup.
I worked 160+ countries with a Buckmaster 8 band OCF QRP. K3NDM and N3HU
have observed its operation with my former ICOM 703, K3 and KX3.
I think Buckmaster uses a 6:1 balun. I have my feedpoint at the peak of my
house about 34' fed with 60' LMR400. The feedline drops down the roof 45
deg then perpindicular to the ground. It is connected to a static arrestor
before being fed back up to the 2nd floor shack. The long leg is supported
by a 14' 4x4 support north of my house but far enough away with a rope the
the end is 18-20' above the ground. The short leg is supported by a tree
up ~20' up SSE of the house.
I used the internal tuner to tweak swr, but have also used the kx3 &
SB-200 to get 200 watts with no tuner with no problems.
Check the specs on the Buckmaster, it might help those trying the OCF setup.
A north to south orientation seems to help me work good dx from Maryland.
73,
Doug, NA1DX
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