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[AC1LC]

Currently using an MFJ2010 6-40m OCF dipole (total length approx 60 feet, short leg 20 feet, long leg 40 feet)for my Yaesu FT450D (internal tuner).  I want to be able to use SSB on 80m too.  I've been thinking about getting a Granite State Cobra Junior 10-80 dipole but I read both good and bad about them.  So, that got me thinking.  Can I just extend the short leg of my OCF dipole so that the now short leg will become the long leg for 80m (approximately 120 feet total length with a 40 foot short leg and now 80 foot long leg)?  Now the other problem is the space that I have available.  If I extend the short leg to make it 80 feet long, the antenna is currently suspended about 50 feet AGL, will it function properly with the 80 foot section as an inverted L?  I gave half a thought of going with a vertical 10-80m antenna but I'm trying to avoid adding radials as the XYL will be running them over with the lawnmower.

[K4QE]

The legs need to be ~90ft/45ft to make it an 80-10m OCFD.

I suggest consulting this URL:

https://www.w8ji.com/windom_off_center_fed.htm

[KI8DJ]

Your 40 meter ocfd should be about 66 feet. 23 feet one side and 43 feet the other so yes extend the short side to 92 feet or so. Actually make it a bit longer for tuning if necessary. Straying a foot or so off on one side or the other will not affect it much. Overall length is important though.  I assume you are using a 4 to1 balun.

[AC1LC]

The legs need to be ~90ft/45ft to make it an 80-10m OCFD.

I suggest consulting this URL:

https://www.w8ji.com/windom_off_center_fed.htm

Thanks, lots of good info there.  I just approximated the 40 ft/80 ft lengths.  I would do some serious number crunching before I started modifying the antenna. 

[AC1LC]

Your 40 meter ocfd should be about 66 feet. 23 feet one side and 43 feet the other so yes extend the short side to 92 feet or so. Actually make it a bit longer for tuning if necessary. Straying a foot or so off on one side or the other will not affect it much. Overall length is important though.  I assume you are using a 4 to1 balun.

Thanks.  Yes, there is a 4 to 1 balun built into the antenna feedpoint.

[K0CWO]

Here is some more reading material:

https://www.dj0ip.de/off-center-fed-dipole/

73, k0cwo

[WA3SKN]

 OK, any OCF is not a dipole, no matter what they claim.
The question is "can you fit an antenna in the area that will work for the band in question?"... and yes you can!  You will not be able to match with the internal tuner.  Get a auto/manual wide range tuner and turn off the internal tuner in the radio.  Try to use open wire or ladder line and not use coax.  Make a loop or dipole not cut to any frequency and with the ladder line and tuner you will be able to match it to almost any band.  Hopefully it will radiate in the desired direction(s).

-Mike.

[AC1LC]

Thanks for the replies.  I'm figuring on extending the existing antenna for a couple of reasons.  1 - I'm cheap. 2 - I like to experiment with antennas. 

But I'm not sure the best way to add the extra length for 80m.  Do I just attach additional wire to the short leg of the existing OCF antenna to get the extra approximately 90' total or do I attach an additional 90' wire and run it out from the feedpoint connected to the short leg at the feedpoint?  My concern is that I'm going to get higher impedance introduced from the short leg and new 90' leg being parallel to each other.  But on the other hand, fan dipoles are set up basically like that and they work.  Or, by extending the existing short leg is that going to degrade the 10/20/40m capabilities of the antenna?  I guess as another option I could attach a new 90' wire at the feedpoint and run it as a sloper or half an inverted V to keep it away from the short leg.  The antenna is currently suspended about 50' up between trees in the backyard but the yard is only 150' wide, so going with the sloper/half inverted V would let me squeeze the extra length in to the existing space available.

Thoughts?

[W1VT]

http://www.arrl.org/pubindex/search/page:4/Merged.call_sign:ve2cv/Merged.pubs:QST;QEX;Ham%20Radio;NCJ;OTA/model:Merged

Double Windom published in QST
AUG 1990 - QST (PG. 28)
Off-Center-Fed Dipole Revisited, The: A Broadband, Multiband Antenna
Author: Belrose, John, VE2CV

http://www.arrl.org/arrl-periodicals-archive-search

http://www.iw5edi.com/ham-radio/2221/double-windom-antenna