[TowerTalk] 160M OCF Dipole Length
w4zw at comcast.net
Sat Feb 25 10:34:36 EST 2006
I decided to try a OCF (Off Centerfed Dipole) dipole for the 160M contest
this weekend rather than trying to put up the extended double bazooka I
normally use. The bazooka worked well but was a single band antenna and I
would replace it after any 160M contest with either a Carolina Windom or a
80M delta loop. Anyway, after calculating the dimensions, I put up this OCF
dipole using insulated #14 wire I got from the Wireman at the Orlando
Hamcation. The center is at about 70' fed with coax and a 4:1 balun, with
the short leg of 86' running to a 50' push-up Rohn mast that I secured in
big Black Olive tree to the East. The other end runs West to the top of my
50' flagpole for about 110' and then I sloped it down for the remaining 85'
and tied it to the wooden walkway to the beach.
Now my question is this. After making this thing longer than I thought I
would need (271') so I could cut the ends to match, I discovered that it was
resonant above the band! Actually about 2.1 MHz. Even with the insulated
wire! I then added 25' that I considered to be an excessive additional
amount to the long end, only to find that it only dropped it to about 1.950
With insulated wire, and one end pretty close to ground (6') I though it
would resonate fairly low so I could start cutting. I have another 50' Rohn
push-up mast that I had already installed on the beach walkway but with
these dimensions, it will be way short of where I need it to be located. I
have my catamaran tied down on the beach another 70' away, and may try
tying one end of the OCF to the top of the mast which is about 35' high.
It seemed to tune OK using the built-in tuner of my FT-1000MP, and I could
work the loud stations but a lot of the weaker guys just CQed in my face.
(But of course, LP on 160Min a contest is a stretch.)
Any suggestions or thoughts as to why this OCF is so long? Could it be too
long such that I'm well into the next phase?
Today is a beautiful day here in SW Florida and I should find the time to
play with this later today.
Jon Hamlet, W4ZW
Casey Key Island, Florida
"A little piece of paradise in the Gulf of Mexico"
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