OCF

Old Codger's Forum. Also called an off center fed dipole.

I was looking online for dimensions to build one or at least an OCF calculator. The basic premise is that instead of feeding it in the center with 1:1, move the feed point over to where 2/3rds are on the long leg and 1/3rd is on the short leg using a 4:1 balun.
I already have a 4:1 that I bought at a hamfest a few years ago and now ended up making the long leg 66' and the short leg 33'. Boy let me tell you what! All the main ham bands really lit up! Even 80m and the AM BCB. 40m comes in strong. 20m comes in strong. 10 meters even (RX tested on 11 since no one was on 10m) was alive and signals were strong.

I want to pull it up through the trees about another 20 feet and get the feedpoint further up in the ether. It's probably close to 30' off the ground at that feedpoint. The long leg slopes up at about 45º and the last 18' is starting to curl down in the trees pointing NW. The short leg points due south, almost a perfect 90º from the long leg and slopes down from the feedpoint to about 25' at it's lowest. I will drop it again to add more coax when I get more coax but my question is, what length should I adjust the elements to? It seems pretty bright as it is on the RX. I have not TX tested it yet as I'm changing things around in the operating position. Any advice well be well taken and I wish I had explored OCF dipoles years sooner.

Charles! Leave it and see if your external tuner can clean it up some. Try it! It may be fine right where it is.

The one I had up before the storms and tree movement ate it up was 90' one side. 45' the other and it played good for as low as it was. When I put up the vertickle, it wouldn't play nice any more then the weather had its way with it, all on a 1:1 balun. I would like to try a 4:1 sometime with new wire up higher and see how much better it would be.

Congrats man! HF is a kick.

I've been using the original Fritzel FD-4 OcF for 10 years or so, 1500 watt version with 1:6.6 balun and incorporated 1:1 choke.
Added coil and length of wire on the short end to resonate it on 1850 so it is working on 160 as well, coil was 180 microH and length of wire after that about 7 meters, cut to resonate on 1850.
Original FD-4 lengths : Fritzel used the shown dimensions of 13.8-m and 27.7-m in the 1960s.
That way i added a band, you can add more bands by just adding 1/3 and 2/3 lengths for the band(s) you want to add like the fan dipole.
https://www.eham.net/reviews/detail/1055
For more details on the OCF look here: https://pa0fri.home.xs4all.nl/Ant/FD4/fd4eng.htm search the FD-4 and read up.

Do you have access to an antenna analyzer, Charles?

Be interesting to see an impedance/SWR plot across the various HF bands.

Nice job Charles. That is exactly the same exact antenna I'm using. It has been a very good antenna for all the ham bands. I did check it out with my RixExpert and did a bit of tweaking, and was surprised how well it looked on almost all the ham bands. Of course I run it through a tuner so the rig sees something near 50 ohms. Without a tuner, the newer rigs throttle back as the mismatch gets worse. However, the older rigs, just like me, don't give a shit, and would probably load up to a 53 Volkswagen with no problem. I also use a 6BTV vertical, and between the two, I do okay. I'm not a serious DXer by any means. If I happen to connect with some DX, I will work it, but I prefer to spend some time talking with new contacts. I'm really not in to the I'm eddie, ur 599, 73, bye shit.

Maybe when I muck out the radio room, we can hook up for a QSO.

I do not have an antenna analyzer but I'll ask around. I may run into one. That's something I should have bought years ago.

I added 30' of coax at the shack end and got the feedpoint up another 20' and into the branches of the giant black walnut tree. The short leg is no longer at an "L" and the only way to describe it would be to say that if you stood under it and looked up, it would say 5 o'clock.
Boy ah tell ya hwat. It sure does hear stuff. If I take it down for for any reason it will be to use heavier wire.

I will experiment with TX over the weekend. Based on how well 80, 40, 20 and 10 come in, I think the tuner will be happy with it. I haven't ever listened to all those bands, including AM BCB, and heard everything without having to retune or switch antennas in the past. The last set up was 33' of window line attached to the same 4:1 balun with 33' leg on each end of the window line and it would ONLY tune up on 80 and reception on AM BCB wasn't nearly so lively. It was good, but not lively. Then, as you tune up the scale in higher and higher frequencies the sensitivity would drop off.

So, to recap, the long leg faces NW, peaks at about 75' before curling down to terminate at 55'. The short leg is almost SE. Maybe, SSE? One small detail, I had to use a 6" double SO-239 to splice together the coax. That's a 6" section with a lot more shielding and it may affect the performance on certain bands as if I had a ferrite shield on that spot and cause the coax to act as a radiator if I had a tuner good enough to tune 160 on a non resonant antenna. This MFJ-948 will only tune on 160 with an antenna that's reasonably close to being resonant on 160. It won't tune an 80m antenna on 160. I've tried in the past. I'll see what happens over the weekend.

See if you can hear AM 1060 out of Calgary. All comedy all the time. I get it reasonably well at the coast after dark.

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Originally Posted by WZ7U

See if you can hear AM 1060 out of Calgary. All comedy all the time. I get it reasonably well at the coast after dark.

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860

1540 AM ... for the India crowd? CHIN.

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CHIN's lineup consists primarily of Chinese (Cantonese & Mandarin) and Italian programming in the mornings and Tamil programming in the evenings and overnight. They also air Albanian, Bengali, Bosnian, Bulgarian, Croatian, German, Greek, Irish, Jewish, Russian, Somali and Ukrainian programming on Saturdays and Sundays.

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https://en.wikipedia.org/wiki/CHIN_(AM)

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Originally Posted by WZ7U

See if you can hear AM 1060 out of Calgary. All comedy all the time. I get it reasonably well at the coast after dark.

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Attachment 15638
By Rudy2alan 14:03, 8 November 2016 (UTC) - http://www.bellmedia.ca/wp-content/u..._funny1060.png, Public Domain, https://en.wikipedia.org/w/index.php?curid=52223362

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CKMX. I hear something zany in there but it's competing with some other station.

Too close or out of the pattern I bet. Some funny chit there. I keep meaning to look for an SDR that gets it solid so I have something other than Pandora comedy. Will update when I discover that SDR on the web.

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Originally Posted by WZ7U

Too close or out of the pattern I bet. Some funny chit there. I keep meaning to look for an SDR that gets it solid so I have something other than Pandora comedy. Will update when I discover that SDR on the web.

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http://websdr.org/

http://kiwisdr.w1euj.com/

http://k3fef.com:8901/

I too am a fan of the OCF, and feed with balanced all the way in. Less fussy with leg lengths. Glad it's working maybe we can hear each other again. :peace:

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Originally Posted by WØTKX

I too am a fan of the OCF, and feed with balanced all the way in. Less fussy with leg lengths. Glad it's working maybe we can hear each other again. :peace:

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When a sched suits you and when 20 or 40 is open ...

I gotta get it up!!!

My antenna, silly man. Not sure how my ground plane will play to you guys, but the whole point of putting it up was to lower my take off angle. Problem is I have a big hill due east, close up which I bet I'm soaking with rf, little of which I'm sure is getting past in a constructive manner. But we can't pass up the rent and we get to keep our furry kids and chickens too. I would need like a 200' tower to get over that hill, damn.

Oh well, you guys weren't talking to me anyway... :lol:

Thanks for finding those SDR's Charles. I really enjoy funny 1060.

Schedule a time and frequency. I will do my best to be by the radio.

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Originally Posted by KG4CGC

CKMX. I hear something zany in there but it's competing with some other station.

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I'm kinda partial to KUNT FM. A little fuzzy but easy to pick up.

https://www.youtube.com/watch?v=tIsnL6xvywI

She loads with the tuner on 80, 40, 20 and 10. Didn't attempt 160. Tested on some online receivers. Furthest being in Texas. I could hear me.

On any or all bands Charles? Sounds like you have a problem like I. I'm lucky to get Dave or into KS or NE.

Well at 3:30 am the only dnab that was open was 80.
And just now I tested out to the West Coast on 20 meters.

2 years later the OCF has come down due to extreme storms in January and February.
I am going to try something similar to the OCF with the 4:1 balun but on a larger scale. The short leg will be about 80' and closer to the ground. The long leg will be 160' or more and set up like a sloper with it going over the trees and then probably curving back down.
Will do updates when they occur.

While researching wire antennas, I ran across this PDF. I 'm not even halfway through it before I decided I had to share it here.

http://k3rrr.com/wp-content/uploads/...asHamRadio.pdf

Quick, put up low-band stuff before the next thunderstorm.

I remember that link. Currently using #57 but 270' long.

Longer feed-line, and with a tuner.

I tried doing one of those those a few years back but I was using a 4:1 instead of a 1:1 and it didn't really work out except on 80m.
But, I'm about to do an "odd-L" with the 4:1, similar to an OCF.

Put it up there and figure it out. I had to mess with the balanced line length.
Calculated/recommended proved off likely due to the shape:

Attachment 16864

Months later ...
Can you do 10m ocf dipole antenna using a 4:1 balun,
short leg 11 feet.
Long leg 22 feet.
I'm trying to get gain on 10m with a wire antenna. If not that, will it work? Anyone ever wonder about this?
Yes, I know the 80m and 40m versions work fine for 10m.

That would be 33 feet length of wire, or 10 meters, good for 20 meter 1/2 wave, full wave on 10 possible if the right choice is made of torroid even working on 6 meters like my full size 80 meter Fritzel FD-4
Feedpoint will be different as mu 1: 6.7 Fritzel balun though, a bit more to the middle of the antenna.
The further you move to the end the more high resistance you get and need a different balun.

One month and eight days later ...

Just going to replace with same dimensions but with 8ga wire. May do some fancy wire tricks but it will still be 33 and 66 with a 4:1.

Eight gauge? I thought I was in overkill with ten gauge thhn for a 75 meter loop.

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Originally Posted by WZ7U

Eight gauge? I thought I was in overkill with ten gauge thhn for a 75 meter loop.

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I have 8ga wire. Stranded copper. Used some on a 10m vertical, doubled over. Worked good then experimented with aluminum cable company coax about an inch in diameter. After a storm last April a neighbor and I waited weeks for them to pick it up after the new stuff went up. Never did and a good amount is still there, hanging in small trees and shrubbery along a street.
Work about as good as the 8ga copper. I expected a huge difference but can barely tell a difference. The copper might actually be better but if you're in a situation were you only have ONE, to work with ... then do what you do and get out the tools.

[edit] I didn't use the coax as a coax. I used it as elements. Unshielded aluminum, porous plastic interior with a solid 10ga center conductor.

[editx2] I say porous but it's kind of a tight cell bubbly interior, white in color, easy to melt with a torch in case you want to flatten one end.