Off Center Fed Dipole (OCF) Antenna - Ham Radio Q&A
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- čas přidán 16. 06. 2020
- I build an 80 meter off center fed dipole antenna for this year's ARRL Field Day Event.
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#OCFdipole
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#PortableAntenna - Věda a technologie
WB4BKO Stretching the wire prior to installation works very well. I use a fence post anchor and then uncoil the wire while walking away from the post while keeping the wire very taut. This has worked for me over many years. My 75/40 meter inverted V has been in use for 20 years and the wire has not stretched any in all those years. Can't say that much about the insulation though. It has deteriorated , but is still intact. I find your videos to be very informative. Even though I have been licensed for almost 50 years, I am always open to learning new things and other hams' interpetations of this hobby of ours. 73 Norm Davis
clearest video on explanation and building one I've seen!
Thank you Michael for this great knowledge on centre fed dipole antenna. Love all you videos as they are so focused to the topic with your exceptional speech clarity.
Have a blessed day ahead.
73
Thank You so much for this. I have the BalUn and the wire connected but was afraid to cut it because I didn't want to make a mistake. Now I think I can do it. No antenna analyzer but my Xiegu G-90 has a little meter that I can use to check my antenna out.
Great presentation! I just picked one of those MFJ-913 from a local HamFest as a back-up and I am very happy with it! Prince Arthur, KB4MIT
Always enjoy your videos, I currently use OCF, I have less then desirable lot to work with, mine is currently inverted vee at 30ft, mine does fine job 40,20,17,15,12,10 and 6m, performs much better than G5RV did. Thanks for input on 80m might just have to make one.
Good stuff. Straight to the point, easy to follow information. Subbed.
I have an off center fed half wave dipole long wire antenna. This is my first HF antenna. I've got to get it up higher and get her trimmed to decrease SWR. I first have to get an SWR meter for HF. 73 from K9POW in eastern Tennessee.
Good video told me what I was looking for . thank you.
Really enjoyed the video thanks for sharing
I’ve got some Spotted Cow in the garage refrigerator right now. I love that beer. BTW, thanks for another informative video, Michael. 😉
Spotted Cow? You're my new ham hero, Michael.
Thanks for the time and effort that you put into this very nicely done video, Michael! Much appreciated. 73, KO4AZY
Good job Michael. I just put up a Maxcon OCF-3K80....GREAT antenna, GREAT price (and about the same length at 133 ft). You can't make one for what Maxcon sells it for. Good Eham Reviews too.
Very nice build! Have a couple endfeds for field day but need a tuner though. Take care
Great explanation Michael. I really appreciate your detail. I have also subscribed here. Many thanks, Mark - NSW Australia.
I see you have great taste in beer Michael. I love Spotted Cow! I always pick some up whenever I’m in Wisconsin.
Lots of good information as usual. I think I might make one but do not have as much property. Thank you.
Very helpful. Thanks.
Thanks for the informative video! Looks like this should work well for FD 2020! Keep the videos coming, 73 - N1UI
Great video Mike.
Excellent content, thanks!
Great video.I also use 80m off center fed dipole I use jetstream 4:1 balun with t240-31 core choke below balun 11 turns rg8x coax also use 90 ft wire and 45 ft wire best antenna I have used.dose need tuner on 80m.I don't get 15m swr too high.I can use tuner though.73s.N9WZL.
You should have some good luck with that antenna on FD. I used the exact same setup for a few years until the MFJ-913 suffered a failure (one of the torroid cores cracked). I then made my own 4:1 dual core balun with big 240 size cores and it still serves as my home station antenna with great results. They can be tricky to tune if you decide to adjust it, but I would recommend to shoot for the bottom edge of the 80M band for best resonance, that should give good fits toward the center of 40M and 20M and so on.
Awesome video. Thanks
Have a receiving antenna use W/a 3oo ohm restor to ground at the shorter wire end to ground. The other(centre wire) end set for 40 meters. And doing well. Switching in or out the 300 ohm changes how it works.
Michael, I am just getting ready to make my first OCF dipole, 80m. This video has all the information I will need. My hope was to trim it enough to get SWR below 2.0 on 80, 40, and 20 - just to be able to use it without an external tuner on my ICOM IC-718. After watching this video I can see the challenges are: A. correct original length; B. Minimum height 30 or more; C. Correct trimming; and, D. Configuration - sloper, inverted V, or ??? - as always, thank you. From S.E. Tenn 73 KQ4IXD
great video thank u
nice job. I go to a park to make my portable antenna. just bring all tools . even wound toroid in a park. soldered the cap. it's fun for me. I do not mind spending time in a park. just hate them bad weather days. but so many nice days to make up for that. that how it is in NY for me. with tuning /trimming off set center fed . had to cut 1/3 to 2/3 off ends. was harder to do then a end fed but take time and got it. I did 40 meter one. got 40/20/10/6 meters. lost 15 meters but put my Icom 7300 in E tune and it tuned it on 15. also 17 and 12 meters. even done 30 meter E tune. the outher off set center is 25% to 75% . or 1/4 to 3/4 of half wave total. ended up with a 6:1 for that one to tune. as you move the feed point the impendence will change. 73's
Super job
Nice video!
Well done Michael. You always look so nervous on camera but your content is outstanding.
Great video. Thank You for explained about dipoles and height! I never understood why everyone said to just put it at 30 feet, but now I know that I can get it too high and cause a resistance problem.
I had great results with most bands on my OCF. Mine was a shorter one for my lack of space. I did have issues with RF in the shack. I needed to put on a choke balun and ferrite beads. I'd use the tuner as needed. Thanks for the video.
How do you know that there is rf coming in the shack?
@@jameyevans29 I get feedback through my speakers and distortion on my outgoing signal.
@@sphexes oh ok I guess I am good with mine. Thanks for the reply
I always wonder about the extra wire used for strain relief. Do you have extra wire on for this and make sure your measurements are just for the insulated ends of the wire?
I listened this weekend for y'all on the air. I hoped to catch you and Ria on the air. Nothing heard?? Great video keep them coming!!! K4AYK #2684 100w and a wire
Nice antenna.
Great video on the explanation and discussion on height vs diminishing returns. My goal is to add an OCF dipole at 3.9mhz to supplement my hustler vertical that uses a 75m coil at the top. So, looking at the OCF and came up with 246' total length with the feed point at roughly 82' OR, 120' total length with a feed point at 40'. Wondering if going to 246' would have any significant advantage over 120' at 3.9mhz? K5KUE
T.y. Michael. I love your videos... they are always so to-the-point. For a long term setup at home, where would you go for wire, and do you think that balun would suffice?
For these portable antennas & demonstrations I use 14ga stranded because it is relatively inexpensive. But it will stretch with long term use. For permanent installation I would either choose 12ga solid copper or copper clad steel wire. The MFJ-913 is a quality balun and I'd use it for something permanent. The Wireman of South Carolina is a good source for copper clad steel antenna wire.
Hey Michael! N4BDW here from KY, been emailing you lately about jpole tips. I actually have the OCF up in my back yard coming from my 7300 ands it’s a great antenna. I pick up mostly north to south better, but I hear contacts ranging from the west coast to several in the Spain area. Great video, very well explained out! 73
Does your 7300 built in tuner tune the antenna okay?
@@garymartin7011 Hey Gary! Honestly I’ve never tried it. I just figured it would struggle, with there being several band options, and internal tuners only match to a certain level anyways. I’ve either always used an MFJ-902B manual tuner, or an MFJ-1949.
I bought a Radiowavz DX80 OCF. Put it up 35ft in the flat top config, What a nightmare, Spent all day dickering with it, nothing was resonate, not even 80. Rig xpert said it needed to be longer than it came outta the box. Never again.
Michael, Would you please describe what you did to your feed line below the balun? It looked like a coax choke and a ??? Thank you for the videos!
It's a series of snap on ferrites on the end of the coax that function as a choke. Technically I didn't need then as the current balun also helps keep common mode interference off the feed line‚ but that's the cable I had with me that morning.
Great video Michael. What antenna tuner were you using? Thanks.
Rig expert AA600
what is the extra loop of wire at the balun ys d for ?
I would love to try a EF or OCF antenna but because of the layout of my yard and my shop I could only run either antenna N to S which would put it out over my shop at about 40' up. Problem is my shop has a tin roof and I've been told that wire antennas don't like being around or over metal.
Put up the antenna wherever you can. You might be surprised as to how well it works. A poor antenna is better than no antenna.
Thank you for the video!
I do have a question... I see a lot of people saying that you need a 4:1 current balun for this and a warning not to use a voltage balun for an OCF Dipole, but nobody seems to have a clear explanation as to why or what happens if a voltage balun is used. Is this something you would be able to explain?
Briefly‚ a voltage balun delivers voltages equally but in opposite phases along the radiator. A current balun delivers current equally in opposite phases along the radiator. A voltage balun may be a good choice for dipole antennas where the radiators are equal lengths because if they aren't symmetric‚ then common mode currents may occur. A current balun is good for filtering out common mode currents so it works well with asymmetrical antennas like the OCF dipole. You can use a voltage balun with an OCF dipole‚ but you will then also need ferrite chokes on your feed line to limit common mode interference. Using a current balun eliminates the need for the choke.
Hi, KB9VBR, a centre fed dipole needs NOT a voltage BalUn but a current BalUn; ie, an 1:1 current BalUn or CMC (common mode current) choke at the feed point.
Even if the two 1/4 lambda limbs happen to be equal in size there may be a tendency for a CMC to flow along the outer surface of the outer conductor of the coaxial cable; because it acts like a third conductor of the transmission line.
In the case of an OCF antenna assuming that the feed impedance to be around 200 ohms (at the normal heights an average ham can manage) a 4:1 BalUn is needed. As you mentioned if a voltage BalUn is used it should be succeeded by a CMC Choke.
De VU2RZA
What was the orientation of your antenna in relation to the map? Just curious. Thanks for the video.
The antenna was pretty much North-South with the longer element pointing north.
There are now tons of info from ham CZcamsrs on this platform. It seems to me that the bureaucrats in dc(aka. FatCats) should be recognizing the advancement provided by the creators more than they are. We have a little hamfest coming up in February down in mouseville I think they should be slipped a note mentioning that there is a movement they are unaware of
Thanks for all your videos!
What was the length of coax you used to feed that antenna? How much coax did you use or does it matter at all?
I typically use RG-8X for HF portable, either a 25 or 50 foot run. Whatever it takes to get from the antenna to the radio. Some say you should optimize cable lengths so that your cable length is a 1/2 wave multiple of your operating frequency. That's fine if you are using a monoband antenna, but makes no sense for multiband antennas as when you change bands, you cable will no longer be optimal. I think you're better off to pick a length that's non-resonant to all your operating frequencies.
Would you recommend making an antenna like this for 20/40 meter, or just making two center fed dipoles for 20 and 40 meter respectively?
Making an Off Center fed dipole for 40 meters will also give you 20 and 10 meters respectively (and 15 with a tuner). Two separate center fed dipoles may be a bit more efficient, but would require more space and a second run of coax to feed it.
Do the end of each leg need to be the same angle from the feed point?
Not really‚ I don't think it's going to matter if the two segments are at different angles
I have tried numerous, and I mean numerous formulas for an Off Center Fed Dipole. This is the first formaula with 133 feet as its total. Most are 134 1/2 to 137 feet, and it does make quite a difference. Using this formula, 80,40,20,17,12,10,6 all have workable SWR, meaning under 2:5.1 SWR. 75 meters I recommend a tuner. If you use LOW power as in under 100 watts you can squeak in 30 and 15 meters using a tuner as the SWR is 5:1.1 or higher. High power on these bands have been reported to cause damage to the 4:1 balun. As for the video, you should remake the video, and study for your presentation. So far this is the best formula for an OCFD, despite 15 and 30 meters being missing. Good luck, have fun, and Good DX. AB9PM
As I recall, in making the antenna, I did use EzNEC to model the OCF dipole, that's how I came up with 133 feet as a good number. But, as you mentioned, this video is more than 3 years old and it's production is lacking a bit compared to my newer stuff. I do have it slated for an update; probably this spring when it gets warmer again.
Just get 49:1 transformer, feed same wire at the end and you get better results. No tuner needed, easy to deploy.
Freedom to hang horizontal, vertical inverted vee or L.
EFHW is better
Not necessarily better, but different.
For a 20m dipole fed with coax. What kind of balun do i need? Thank you.
A center fed dipole will have an impedance of about 70 ohms. You can direct feed it with coax but a 1:1 balun will help keep common mode currents off the feed line.
What type of coax did you use for the lead-in? When you measure the length of each leg, is the measurement from balun eye-let to insulator?
I used 50 feet of RG-8X in that video. As for the measurements, I used the figures derived from the standard dipole calculation (468/F in Mhz) and shifted the feedpoint so one leg side is 67% and the other is 33%. The dipole calculator assumes bare wire, but I used insulated wire, so you should factor in reducing the length by about 4% for velocity factor. I usually don't as that extra 4% of length gives me a bit of working room to attach the legs to the balun and end insulators. Better to be too long and trim to resonance than to be short and have to make up the difference.
@@KB9VBRAntennas For a permanent installation, would you recommend solid wire? Would 14-AWG be large enough?
What did you use to get the antenna up?
I use a Weaver throw weight. It's a 12 oz shot filled bag that arborists use to put lines up in trees: amzn.to/2CigRek
What could I do to be able to reach my brother in Alabama on my 1996 mobile TRC-485 set up in my home as a base station, here in Indiana? I'm trying to get back on the CB wagon, like I did back in the day! I need an idea either on the antenna setup or a power boosting method without blowing my mobile unit! Thank you for any ideas!
A solid, reliable connection between Indiana and Alabama is going to be wildly unpredictable on the 11 meter band due to the signal propagation. We are near the bottom of the solar cycle so throwing power or unique antennas won't necessarily fix the issue.
You got 1.6 on 40 meters and 2.0 on 20. Based on on those numbers, would it be safe to assume 30 meters would be 1.8? I'm hoping to build one of these for 80, 40, 30, 20.
Not exactly. I'm not able to attach a chart, but if you look at a broad frequency sweep of an Off Center Fed dipole, you'll see a series of peaks and valleys. The valleys are the low SWR spots that roughly correspond with the amateur HF bands and the peaks are the higher SWR spots outside the amateur bands. On bands that are a frequency multiple, like 80, 40, and 20, you'll see good SWR spots; and on odd frequencies, like 30m or 12m ,you'll see higher SWR. I do not remember sweeping the 30m band on my OCF, but I recall when I modeled it using EZnec, that the SWR was about 4:1. It's not ideal, but workable on 30m with a tuner.
Do you trim at the outer ends and how much at a time?
You can trim the outer ends until you get your desired amount of resonance or tune for the frequencies you are looking for. Trimming would be proportional on each side, for example: if you remove an inch on the long end, you'd take off a 1/3 inch off the other.
I'm thinking about building one for the 10 and 11 meter band because the landlord doesn't want anything attached to the house or roof so I was thinking about a dipole I have a really tall pine tree in my yard do you think this would work ok on a cobra 142 gtl on 11 meter.
A simple dipole for the 11 meter band will be approximately 17 feet long from end to end. If you use a relatively thin wire, it should be relatively hard to see from the ground.
KK7EQB --- SE Idaho I'm still a rookie at this, going on about 2 years. I'm planning an OC dipole for my back yard. I'm limited to about 10-15 ft of height due to trees and power lines and a length of about 40-50 ft. I have a 4:1 balun but from what I''ve read, maybe I should just use a 1:1 balun because of the height of the antenna. I have used a CF dipole for the last year but so far I can only receive but no one is hearing me on HF. It seems to work fine for 2 meters and 70cm locally. Any suggestions?
Balun what is the difference between current and voltage
Good luck on field day
Briefly‚ a voltage balun delivers voltages equally but in opposite phases along the radiator. A current balun delivers current equally in opposite phases along the radiator. A voltage balun may be a good choice for dipole antennas where the radiators are equal lengths because if they aren't symmetric‚ then common mode currents may occur. A current balun is good for filtering out common mode currents so it works well with asymmetrical antennas like the OCF dipole.
Cool video to get 88 feet what math formula did you use how did you get 44 feet as well cool video
How is this preferable to an 80-10 m end fed?
I'm not sure if it's preferable‚ just different. Couple advantages is that the OCF doesn't require a counterpoise for operation and the impedances aren't as high at the feedpoint. That is‚ you can use a 4:1 balun with an OCF while an end-fed may require a 9:1 or higher balun.
I am interested in purchasing some electric fence insulators similar to the ones you have. As you said you went to the local feed store to get them. I have looked on Amazon as well as the other ham related Internet retail outlets and only the "doggone" version are available. Would you like to recommend an Internet source for the electric fence insulators?
These are the insulators that I use: www.fleetfarm.com/detail/zareba-white-high-strain-corner-post-insulator-10-pk/0000000281955?Ntt=fence%20insulator
I don't know if you have a Fleet Farm in your area, (they seem to be an upper midwest thing), but Tractor Supply Company should have something similar.
@@KB9VBRAntennas Thank you Michael. You are correct, however we do have a Tractor Supply Company in the area. 73...Rob (wd4ift)
Hey mike, what kind of wire you are using ( number or model ) please. 73’s
I use 14 gauge THHN stranded wire for the antenna elements. It's commonly available at a home improvement store. But if you are thinking of a permanent installation, and are concerned about stretching, you can switch to 14ga solid or even copper clad steel. The stranded is just a lot easier to work with.
@@KB9VBRAntennas thanx man 👍🏼
How do you “ connect “ the insulators?
The end insulators? You can use a variety of methods, from tying knots for temporary use to a double barrel crimp ferrule for permanent installation.
If I want 7mhz as main band, is coax centre to short or long leg , please? m6baq, thnx
I don't believe it makes a difference. In all the OCF transformers that I've seen, no one has indicated that you attach the long end of the wire on one side or the other.
Thanks!@@KB9VBRAntennas
Or run a big doublet with ladder and do away with lossy coax.
How about 60 meters?
It is channelized into 5 channels at a 2.8 kilohertz bandwidth with a maximum radiated power of 100 watts relative to a dipole
Spotted cow?
Brewed in New Glarus Wisconsin‚ Spotted Cow is an amber ale with a profile similar to New Belgium's Fat Tire. It has a bit of a cult following as it is only distributed within the state. Residents of Chicago and the Twin Cities have been known to 'bootleg' it across state line.
KB9VBR Antennas I tend to bootleg it to Iowa too. I’m heading to Toppling Goliath in Deborah next month, but I’ll be driving up the Wisconsin side of the river to pick up some more SC on the way.
I've heard of that stuff. We're camping in the Mississippi valley later this summer‚ I might have to make a side trip to the brewery . . .
Proprietory baluns look great but they are notoriously Inaccurate to the point of often being useless.
What's your point? Are you saying the MFJ balun is no good? I doubt there is anything 'proprietary' about it.
Man update the wire stripper.. lol DE AA2YG
Yeah‚ I seemed to grab the garbage stripper for that project
B
Slow down, you have so much to say and trying to get it all out,, Myself being a newbie it was kind of hard following you. I know you really want to get good information out there, please just slow down
My videos can be dense with information as I edit out the repetition. Feel free to pause and rewind if you miss something.
THAT DOES NOT WORK .
TO BELIEVE THAT A PL CONNECTOR CAN HOLD THE WEIGHT OF THE COAXIAL CABLE IS RIDICULOUS
Terrible readings for SWR! This antenna is not tuned right and should be cut to get down below 1.5 to 1. Any antenna will work usually but taking some time to tune it properly can really make a difference. Why this guy made this video I don't know but it is not a good example for new hams. Terry
I think you missed the larger point of the video. Yes, you can get the SWR to under 1.5:1, but when you do your antenna is committed to that location as the SWR will change when you move it. As I said in the video, the most likely reason for the slightly high SWR was the height of the balun as it was below the 30 foot height that is recommended for off center fed dipoles.