Off-Center Fed Antennas

Ted Edwards (W3TB) gives a detailed presentation of the properties of a multi-band off-center fed dipole antenna. The antenna described is only 68 feet long, but covers the 40m, 20m, 15m, and 10m amateur radio bands.

Record on 4/8/2023 during the April WCARES meeting.

[kosmamoczek]

I built the 40m, 40.6% version as my first proper antenna. The learning curve was steep, but the results are fantastic for a piece of wire hanging on a balcony - the convenience of freely hopping bands won my heart. This explanation made me finally understand *why* and *how* it works - and the next one will probably be a custom modelled one because one must never stop learning. Big respect for Ted.

[donaldshields]

I have an off centered antenna built by high HY antennas in Pennsylvania and it covers from 80 m to 10 m and I have to touch it up just a very little bit with my inboard antenna. Tuna on my Kenwood 590 and I get very good signal reports It’s mounted about 35 feet in the air and that antenna will handle up to 5000 W and if you look up high-powered antennas, you will see a lot of information on that. Thank you for your show. It was very good K1 Emw in Maine seven threes

[GWVK]

Excellent explanation of the OCFD, my main QTH antenna.

At school, the x-axis went left to right, and the y-axis went up and down. I'm in the UK.

Thank you for the presentation.

[michaelrogers]

Ignore the trolls. Great video. Thanks for posting. You are an excellent speaker. I'm glad I watched!
73, N4MJR

[MirlitronOne]

I'm in the UK. Soon after I started HF about eight years ago, a friend recommended that I try an OCFD aerial fed at one-sixth (17%) along its total length with a 1:4 unun. I made it 21 m long with the feed point at 3.5 m from one end. The result is an aerial that works on 40m, 20m, 15m, 10m AND 6m. It needs help from an AMU for the 40m and 6m bands but works very well on them all and I've had QSOs from all over the world. Strangely, it also matches at the high frequency end of Top Band (160m), not efficiently but adequate for the local club net.
[Incidentally, please don't blame the MMANA-GAL X/Y coordinate thing on the Brits. It's the wrong way round for us, too.]

[fm]

Dear sir, thank you for this video. I have been very interested in OCF antennas, making them in particular. Your presentation was helpful. It is embarrassing that the ham world has its share of negative commenters. Please ignore their sad efforts. Best wishes from S.E.Tennessee, 73 KQ4IXD

[jameskioeb]

Like the talk. I learn so much that I might need to make one of these…

[rickmckee]

It's "Common Mode Current", not common current that flows on the outside of the shield. Then there is differential mode current that flows on the center conductor and the inside of the shield.

[ABVampire]

Anybody? I'm tripping over the terminology "Balun vs Unun" when it comes to OCF's. This video @11:25 shows a Summary reprint of a 1988 QST article on OCF's and the transformer is identified as a "4:1 current balun". I learned to respect without question the tech stuff in QST but is their use of the word "Balun" is a poor choice of words or am I mistaken? I'm in the midst of an OCF install. My wire is up but my 4:1 Balun /CMC choke combo (copied from TRX labs on YouTube) complete. swr's bad when up in the sky. On the bench with 200 ohm it's wonderfully flat 10-40m. Should I rewind the balun section of the TRX Lab's design to be a proper 4:1 Unun?

[timdbl]

At 9min 45 seconds: I think the capacitor is to bring resonance up in frequency a bit on 40m; I've used this technique to good effect on other OCFs. The capacitor is at or near the current anti-node on the lowest frequency. Because of its position and value, it is almost negligible on harmonic frequencies.

[Redbelly]

The OCFD Is the reason I use a 132 ft EFHW. 😅

[saxmusicmail]

Like Ted, I'm a big fan of OCFDs. I'm often asked to help other hams with theirs. And I've abandoned the 1/3-2/3 split long ago. Anyway, I'm always surprised at how many hams not familiar with how an OCFD works that think they can trim 40 meters by adjusting length of the long wire, and adjust 20 meters by adjusting the shorter wire. This is NOT how an OCFD works, you can not adjust bands individually like with a fan dipole.

[garrettmoser]

Are these in Magnetic or True for 45 degrees and 150 degrees?