Okay, as I noted before, my first antenna wasn’t a dipole. But I’ve worked with lots of new hams, and a dipole is cheap, quick, and easy to construct. But, you say, dipoles are only single-band. Yep, and I recommend the 40m band.
Why 40? For several reasons:
- The antenna isn’t really all that long, just 66 feet
- The band is often open in the evening
- Unlike 80m, which is full of nets, 40m is more open and you can call CQ and hope to get an answer
- If you want to play with digital modes (such as radio-teletype or PSK-31), there’s a fair amount of activity
- If you want to try out your Morse code, there’s a spot on the band where people use slow code.
So, what does a 40m dipole consist of? Well, 66 feet of wire, split in the middle. You can use pretty much anything for wire as long as it’s a good conductor. I don’t recommend house-wiring type wire because that’s soft-drawn copper and will stretch, but if that’s what you’ve got, by all means use it. Radio Shack sells bare stranded copper wire made specially for antennas, but it’s a bit pricey. You can use either insulated or not—it doesn’t matter.
An insulator goes at each end and in the middle—electric fence insulators work fine and are dirt cheap. To each insulator you’ll tie rope to hold up your antenna.
The RF feed point of a dipole is in the middle, so there’s 33 feet of wire on each side. Yes, this is a balanced antenna, and coax is unbalanced, but I still recommend you solder the coax directly to the antenna. The shield goes to one wire and the center conductor to the other. This is a tried and true method and it works. You’ll want to cover this well with electrical tape and also make sure that the coax doesn’t hang by the soldered connections, but rather by something physically tied to the center insulator.
There are two ways to mount the antenna. The first is to get each end up as high in the air as you can so that the antenna is a straight line (it’ll droop a bit in the middle). This is the standard configuration. The second is to get the center of the antenna up as high as you can and pull the ends out as far as you can get them. This creates an inverted V configuration. Either works.
Safety comes first in either case. Make sure the antenna is high enough in the air no one will run into it. Further, if you use bare wire (which is fine, by the way), the ends of the antenna is where the high voltage is, so keep these up and out of reach! And do not go even close to electric utility lines—getting to close creates noise anyway. Sadly, hams have been killed ignoring this guidance.
How long should the coax be? The standard answer is “as long as it needs to be to reach the transceiver!” And you can take that literally. There are no restrictions. And on 40 meters (7.1 to 7.3 MHz), coax line losses are so low that they aren’t worth bothering with. What kind of coax? I happen to be particular to RG-8X, but RG-58 works too. The stuff you get at Radio Shack kind of skimps on the braid coverage, but will work.
Put a drip loop where the antenna enters your house. Slamming a window on the coax is not a good idea as coax really doesn’t like to be squeezed. I bring my coax through a vent into the crawl space, then I pull back the carpet and drill a hole near my desk. I push the coax up through this. Pushing the carpet back keeps cold air from coming up through the hole. Make sure you have enough slack that you’ll be able to move your transceiver around easily.
Now is the time to solder the connector, usually a PL-259, to the end of the coax so you can connect this to your transceiver. Don’t scrimp on the connector—get the silver ones like these at Ham Radio Outlet—order several as you’ll end up using them! And make sure to order the reducer—RG-8X and RG-58 take different reducers. You’ll want to make that connection where you can reach it easily, as you’ll want to disconnect the coax when thunderstorms are near. In fact, during the summer, I leave my antennas disconnected unless I’m actually operating, and I don’t operate during thunderstorms! Yes, I’ve had lightning hit an antenna and yes I had to repair some damage.
And that’s all there is to it! This is a great first antenna! Your next step, after getting some air time, will be to insert some traps in that dipole so you can use it on 20-meters. Oh…you can use the 40-meter dipole on 15-meters without modification.
Do you need an antenna tuner? Nope. The antenna is close enough. If you happen to have a tuner, then by all means use it. In another post I’ll talk about trimming up that antenna so it has a low SWR, but with a simple 66-foot antenna, you’ll be close.
I did a video on this based on your question. You can see it at https://youtu.be/aUe5v0hOT48.
It is wise to add a 1:1 balun at the feed point? Or is that not necessary? I’ve read that without it, the feedline will become part of the antenna.
The building of the antenna is fine but as with nearly all the video I have watched the final connection from the coupler wires to the actual dipole antenna wires is never covered. We see the coupler and the insulators maybe even the tethering ropes but not how to make that final connection from the center point coupler to the dipole antenna coax. Do you know where I can find information as to how to make this (these) connections?
Gordon P. KO4OCO
You can fold it back even though it’s insulated.
I made use of your page and a 3D printed center support and insulators to build my first antenna. Put it up yesterday and made several POTA contacts. This is my first antenna and it’s working great for me.
Pic of the antenna in this link.
I’m making one of these dipole antennas and have a quick question. I’m using 16 gauge speaker wire, 3d printed insulators and the connector. When I go to tune it, will I need to stript back the insulation on the ends of the wire when I fold it back on itself? Does the concuctor have to be touching at the ends? I’m not sure if folding back the sire with the insulator on it will mean that the folded back portion is an extension of the element or not.
I wish to put up a 40 meter center fed dipole, but after considering space used by the end insulators and balun, I can only come up with 63 feet of wire due to space limitations. Would that be a serious drawback? I do use a tuner.
Lots of people do put in an SO-239 at the midpoint. I do that too. But if you want you can attach the cable directly.
Can you please let me know what i connect the 40meter wire diapole too when i cut it in half. Is it the so239? your video had a bad angle while i was watching it. its the one where you had to solder all the extra wires you had laying around the shack. also can i attatch other to the same so230?
Thank you for your help
I am assuming you mean two bands: one for each band. Yes, it should work.
kc0ogg here, name is Rick.
I was wondering if one inverted V could be used in conjunction with another inverted V?
Almost like stacking. One running north and south, the other running east and west using the same center fed coax either direct connect or thru a balun or wired separately( 2 baluns and 2 feed lines) and fed thru a duplexer? Center point would be ran off of a single mast for both V’s. Or am I looking at interference from them being to close to one another?
For new beginners on making antennas also should know: When measuring the legs of a simple dipole is to measure from the holes of the center insulator where the wire goes through and where the wire goes through on the end insulator. For example: I have built MANY antennas with the Alpha Delta C center insulator and when I make the antennas I calculate from 7.200 phone portion. From the mounting hole to mounting holes is where I measure from and I don’t include the length of the center insulator. The wire don’t see that portion and only sees the wire length. 65 feet total yes, each leg 32 feet 6 inches yes. Also the antenna does not see the wire wrapped 4 or 5 times to make a strain relief and to be soldered to the spade lugs. I have helped many new hams get confused on this. This comment was for any technicians who have asked about this to me in the past. All my antennas are measured this way and are ALL resonant with a flat SWR across most portion of the phone part. (7.125 1.1, 7.200 1.0, 7.295 1.2 SWR)
Those dimensions sound good to me. 65 feet is a good height.
Thank you Dave for your hard work and support! Still a tech but general is fast approachin’
The 2m repeaters in my area are dead and I’m looking forward to get on 40 meters. I speak German and some Russian, so talking to the fellers overseas in their native tong sounds exiting. My rig consists of ICOM 7300 and a 1500 W automatic antenna tuner (MJF). My ham club suggested a 102 feet ZEP antenna for me (center fed) with a ladder line 450 ohm. The height in my trees would be at 65-70 feet. There is room for a 140 foot long antenna and also other trees for even longer. But height is very limited above 70 feet. This sounds like a great compromise if I can get it to work. What say you any input you can give me?
Love your channel! 73 Val KN4TQN
Dave, I”m new to ham radio and trying to learn as much as I can while studying for my license. Would this type of grounding would you recommend for this type of antenna?
I suspect the large frequency difference will keep the two antennas from interfering with each other. The only way to know for sure is to try.
I have a free standing EMF mast with a vertical dual band for VHF/UHF at approximately 25′. I just passed my General and am about to install a telescopic mast with a multi-band dipole (10-80m) at 50′. I plan to install the telescopic antenna very near the existing dual band antenna. Question: will the metal mast of the telescopic interfere with the existing dual band. Should I take down the dual band and install it on top of the telescopic antenna? I will be running a Yaesu all band transceiver. I really enjoy your YouTube videos.
Thank you, Allen KG5TRM
I hope this wasn’t mentioned elsewhere, but I have two suggestions. 1) If a newcomer is not handy with soldering, why not get pre-attached connectors and cut one off with a few feet of coax still attached? Then, run the long coax down into the floor. He would have the beginnings of a new project waiting in his parts box, and not have to solder the connector. 2) Why not use a 4:1 balun with a 64%/46% cut and have an off center fed dipole that is good for at least 4 bands or more without a tuner? I will admit that a 20m homebrew dipole was my first antenna. I got Russia and a lot of Europe from the high point at 13′.
Scott, that works too. 73
Great article. One question though. What about not connecting the antenna directly to the coax but via a SO239? Thanks for all of your help. Your articles and videos have been an amazing resource. 73 KN4BVP
Thom, the metal roof will most definitely affect the antenna if the antenna is erected over it. You will have to experiment with it to see how well you can adjust the antenna for lowest SWR. Note that the metal roof will act in many ways like an artificial ground. So the actual height of the antenna will be the height above the roof. The heights you are suggesting would indicate the antenna elevation pattern will be very high. This is good for NVIS work for close-in stations (within a few hundred miles). Again, experimentation will give you more info than any theory can. Good luck! 73, Dave, KEØOG
Very useful article . By the way, I am planning to set up an inverted- V , single band on 40 , CW portion. The question is , I have a metal roof . I want to set up a tripod mount along with tv masts to bring up like 10 ‘to 12’ , the total height above ground would be 30 ‘ at the center feed . Would it be a problem with SWR due to the metal on roof or what else I should be aware of ?
Look forward to hearing from ur suggestion or advise.
Lee, take a look at this page on the ARRL website: http://www.arrl.org/hf-trap-antennas. Also, you can look around on the Internet for various ideas for trapped dipoles. Hope that helps. 73, Dave
What kind of traps to make 40 meter dipole
Work on 20?
Thanks Dave. I will keep looking around for some rig. No hurry.
Hi Walt, nearly every HF rig these days covers all bands from 160m to 10m and sometimes 6m. I don’t recommend used equipment for new hams, but if budget limitations make used equipment your only option, then I recommend that you consult experts in your local ham radio club. Buying used equipment online can be a pig in a poke (you don’t know what you’re getting). Tube type equipment is popular among some hams, and certainly these old rigs can be made to work. But almost always some restoration is required; this is an art in itself. The least expensive new rig out there is the Icom IC-718 for $599.95 at HRO as of this writing. Next is the Alinco DX-SR9T/E, although QST didn’t give it a glowing review. HRO carries it for $679.95. The next most inexpensive rig, the Yaesu FT-450, is available at HRO for $749.95. Note that all three require an external 12vdc power supply.See my video on station setup at this link. Be aware that the rig itself is only part of the expense of putting up a station. You must consider the power source, cabling, antenna, etc.
Wanted: a real cheap rig I can get on 40 meters CW with. Can be an old Tube type. I am on a very tight budget!! I passed my Extra Class exam on first try last year. It was easy! (Navy electronics background helped!). I have been off the HF bands for years. anxious to get back into Morse. Maybe later SSB. Thanks for any help.
PS: I am looking at Craigslist and Ebay too.
Cave in Rock Il
Hi Dale, there is only one size SO-239 that I know of. I usually solder the coax directly to the antenna. An example is in my first Ask Dave video at https://youtu.be/ts2nkCDIS4s. Instead, if you wish, you can bring connecting wires from the insulator down to an SO-239 and solder that. Be sure to add strain relief so the weight of the cable will not be borne entirely by the SO-239.
With this great I found I’m ready to try a 40m dipole. I ordered so239 came today and 10, 12 or 14 ga will not fit into the so239 to soder. Must be junk as coax won’t even go in it to soder so239 is just too smal. What is the proper size so239 do I need for 10 or 12 guage? 73s
km4htd. Dale in Kentucky
Hi Ranjit, The ARRL publishes the Antenna Handbook, though it’s rather expensive. If you search the Internet, you’ll find articles about beam antennas and how to construct them. 73, Dave, KEØOG
I am from Sri Lanka. Thank you very much for the nice technical article with some safety advice too. After obtaining my license some years back, I was operating only on VHF. Here there are no Ham Radio equipment traders. So only now that I started my HF. I really appreciate your article. Have you published any simple HF Beam article we could build at home? If so please send me a copy.
Try the ARRL Handbook or the ARRL Antenna book for construction details. Or, you can get pre-built trapped dipoles from MFJ and others.
Good info. Can you tell me about the traps for 20M or where to learn about them?
Tnx es 73 ND3B
Great intro to antenna building. I have had an expensive multi band vertical in the past but it was a hassle keeping it in repair during snowy winters here in the Idaho mountains. Good old dipoles work fine, are cheap to build, and are maintenance free if the trees they are suspended from don’t fall down (have had that experience).
I enjoyed looking at your multiple motorcycle trail maps. I have ridden many of them on an Ossa Pioneer and Husqvarna when visiting Colorado on vacations from Kansas City. Your article brought back many memories. Idaho is more dusty and the trails rougher, with none of the big peaks over 14,000 like yours. But as they say, there’s no such thing as a bad day on a motorcycle.
Thanks for you input. I had not thought about the noise aspect on leaking of the high voltage lines.
Hard to say – it depends on how well the high voltage wires are maintained. Perpendicular is good. Of course, the further the antenna is from the HV wires the better. If you have absolutely dreadful noise on all bands, contact the utility – the noise is a sign that they’re losing power because of arcing or maintenance issues.
I have high voltage wires about 150 from the 40 meter antenna I plan to put up. It will be at perpendicular to the high voltage wires. Do you think this will be a problem?
Thanks for info Dave. I always close off the ends of any conduit, we have those critters here also and they love to find homes in small places as Fall approaches ,even in carburetors of snow blowers.
No gotchas, but keep rodents out of the pipe. Sometimes they like to chew on coax. Note that a lot of coax is rated for direct burial. Be sure the coax isn’t nicked or water can leak in and ruin the coax.
I am new to Radio Amateur, just got my General Class in April, no transmitter yet, but looking at Yaesu, Kenwood and ICOM to see what I can afford in an all bander. Your article was one of the best that I have found on the internet, short, sweet and right to the point and answered all my questions about a 40 meter dipole without reading a novel!! My antenna will be about 50 feet from the entry to my house and therefore will run underground via sched 40 3″ pipe to allow for future wires. If you know of any “gotchas” with underground running of coax, I am all ears Dave.
Nice article…straight to the point and easy to follow. I got my Technician license in 2002, quit after a couple of years of 2 meter repeaters and not being able to get past the code part. Just got back in, passed my General class test and wanted a good easy antenna to hook-up my Swan 700cx that a good friend of mine gave to me. Look like this is where I will start.