KM4ACK End Fed Half Wave Antenna Build And Review

[@HamRadioCrashCourse]

The power limits on the antenna is 50 watts ssb and 20 watts cw/digital.

[@andrewhamop6665]

Thanks, was just about to ask that. As soon as you showed the price I was like "shut up and take my money" might just have to add this antenna to the holiday shopping list! Thanks for the build guide, 73 de W8IJC! Oh and of course you could safely run higher power with some higher gauge wire on the un-un and radiating element.

[@donaldsmith3048]

That sucks. What do I need to do to get it to work 100 watts? I am thinking big transformer core and wire. I want something that I can run full power with my IC7300 without having a problem!

[@KU9L]

I usually mess up something in building a kit, while it was painful watching you assemble the kit without instructions I have watched 4 other videos successfully building this kit so I know I will be successful! Cheers es 73, Dave - KU9L

[@HamRadioCrashCourse]

It’s a dead simple design. Even with my mess ups, it worked fine. Would recommend.

[@Bob814u]

Easiest antenna build I have ever done. I got the package open and was looking at all the parts. I started watching the video while winding the toroid. Before the video was over it was time to solder everything together. Soldering done, hot glue applied, and out to analyze it. I ran it up the DX Commander expedition pole and down to a electric line post. Hooked up the analyzer, walked over and wrapped a couple of wraps around the plastic of the 'pole' and it was done. My only thought was "That's it?"

[@sethproaps8899]

I wanted one bu the store was out, so I sourced the parts, I have no idea how he sell em, he is selling just above having a loss, a true humanitarian

[@noname-qf8jg]

Looks like a pretty good low power portable antenna. Translucent cable ties are for indoor use only because they decompose under the sun's UV. Some of the other videos show black cable ties. If you only use it on Field Day then it probably doesn't matter.

[@stridermt2k]

Thanks in advance for making this. I know it will encourage others to build antennas. It really is a lot of fun! A preemptive like because I've seen enough of your videos to know where you are coming from. I run a 49:1 end fed and really love the thing. It's NVIS at just 12 or so feet above the ground, but it gets out. 5 states away from WAS. 1.3:1 on 40, closer to 2:1 on 20. It took a little tuning but once I got it dialed it in I have had no problems with it. This looks like a fun and useful build! 73 de N2NLQ

[@EyeKnowRaff]

6:02 the wire: Twist me harder, daddy Me: 🤦‍♂️Dammit, the wire has a kink.

[@J0HN3]

Recently used one of these for a POTA activation. It worked well.

[@thomasmaughan4798]

I imagine forty people have discussed or questioned the non-existence of a "counterpoise". There is always a counterpoise or it is not going anywhere. Since the design is an *autotransformer* there's a common ground point; namely the shield of the coax. That's your counterpoise. So is your body if you are holding the radio or microphone.

[@SteveBerwick]

Hi Thomas, I've been using this EFHW with a lot of success running QRP. In fact I'd argue it is my best antenna for my ic705. However, I am also interested in the counterpoise aspect. I have grounded my radio before, with zero noticeable effect on Noise or Signal Strength. How would you recommend running a counterpoise with this type of antenna?

[@thomasmaughan4798]

@@SteveBerwick The transformer or toroid device used at the end of a halfwave antenna usually has a grounding lug or wingnut, that's where you attach either a counterpoise, or earth ground, or both. There must always be a completed circuit. Theory of operation: The radio sends its signal to a toroid ferrite transformer primary winding. This excites a magnetic field in the toroid. As far as the radio is concerned, it's done. The secondary winding of the toroid is connected to the antenna but of course only one end of the secondary winding goes to the antenna. The other side of the secondary is grounded. If you have not provided an earth ground or a counterpoise, it will use the outer braid of the coax as a counterpoise. If you block that with a choke, then there's no source of electrons to push into the antenna and it will fail. As to the length of the counterpoise; I have several rival opinions what is likely to work best. Quarter wave counterpoise will give it low impedance, and on the ground side that is probably what is wanted. The coax should be choked near the antenna.

[@KB0OTY]

Jason's been doing some good work.

[@bereadyeveryday6764]

I hope he gets more of these kits in stock. Really want to build one of these for 10m

[@Bombguy83]

Looks like you were watching COPS before you did the intro. Thanks for the build vid!

[@Pigeon__Man]

Just ordered mine. Was looking at the Emcomm III, but for the amount of use it would get it was a bit out of my price range. This looks perfect for my use case.

[@RobDTom]

EFHW antennas are very efficient. I’ve made contacts all around the world with mine using only 100 watts

[@K1STG-Fred]

I bought one of these antennas based on this video. I can't wait to build it.

[@mark2727]

Save yourself some headache's and test the toroid winding before attaching the antenna wire. With the toroid wound per instructions with the capacitor properly soldered in place, attach a resistor from ground to the antenna connection (200 - 450 ohm). Use a uhf male to male adapter (BNC or PL259) connected directly onto the antenna analyzer & the antenna feed point. Sweep the band frequencies of interest for lowest SWR & document the results. Your Impedance |Z| should be as close to 50 ohms as possible, & R-resistance readings at 50 or less. Adjust winding as needed, or if the band sweep shows 1.2:1 swr then connect the antenna and rescan the bands of interest. Tune the antenna for best SWR in the band of interest. 73's de kd5smf

[@thomasmaughan4798]

For a 49:1 toroid you probably ought to use a 2200 to 2500 ohm resistor to match a 50 ohm source. For a 9 to 1 toroid is where that 450 ohms resistor comes into play.

[@timk7749]

I have this antenna and love it. If you've never built one before I believe KM4ACK provides a link to his step by step build video. 73 de KF7VUT.

[@StuartM0TTQAmateurRadio]

I've made a few different 49:1 transformers and generally to get the minimum SWR in the right place on the higher bands, I've needed to have the SWR minimum slightly below 40m. As you found, the SWR bandwidth on 40m is still perfectly reasonable.

[@TEGEscalator]

Greetings from Belgium 73 👍

[@paulhastings3109]

He is out of stock for now but I was able to get my name on his list. Pick-up a 991a for portable and emergency. Do have a g 90. Just wanted to get outside. Being in Florida is the best time of year. Is a beach a park have plenty KQ4CD Paul

[@dougdunlap5889]

what is wattage ratting?

[@donaldsmith3048]

That is for a half wave antenna, what band? With the wing nut it would make it easier to change the wire for different bands. Just a thought, maybe I am wrong. I am wrong a lot!

[@brentjohnson6654]

I believe it is half wave for 40m. So it is multiband for 40, 20, 15, 10 because of harmonics. Pretty good.

[@thomasmaughan4798]

@@brentjohnson6654 "So it is multiband for 40, 20, 15, 10 because of harmonics" You are going to have some creative LOBES on the higher frequencies. You could probably calculate radiation patterns using EZ-NEC. But yes, more consistent results with wires cut to the proper length for each band.

[@chopperboi89]

What's your opinion on 9:1 vs 49:1? Is there an appreciable difference?

[@HamRadioCrashCourse]

49:1 is for a half wave end fed antenna. I always go half wave end fed over a 9:1 “random wire” antenna.

[@chopperboi89]

@@HamRadioCrashCourse Danke schön. I've not found any conclusive information comparing the two. P.S., Found you from your work with Modern Rogue. 73 DE N2VNP

[@thomasmaughan4798]

The ratio is irrelevant to antenna performance but is dictated by where exactly you feed the antenna. At exactly half wave, the ends are high impedance. It would be infinite except radiation from the antenna reduces the end impedance. So that's where 49 to 1 transformer comes into play. 9 to 1 is to be used where your antenna feed point is NOT at the end. But suppose it is anyway. What then? Well, it still isn't, and the residual current is going to travel down the coax. But it does that anyway. Where's the circuit? The primary of this transformer is 2 turns, center conductor then 2 turns then outer conductor. That's the drive. But the secondary is 14 turns or so, one side of that goes to the antenna, the other side is soldered to the same end as the primary, and thus the coax shield or outer conductor. When you induce a current in the high impedance of the transformer, lets say you push electrons into the antenna for half a cycle, where did they come from? The coax, and possibly your body holding the radio or microphone, and the battery cables and any other current path that shares the common side of the autotransformer. Not only that, but it's high voltage! That's why you see this design only on QRP atennas. Who cares about the 20 watts of RF on your body? That's insignificant. Since the feedline coax is part of the antenna, its length and where you lay it becomes important. You can avoid some of that uncertainty with a "counterpoise" (radial) at the transformer ground point AND an RF choke (ferrite on the Coax or a "ugly balun" choke of some turns of coax; how many depends on the band you are using) to keep the RF current from running all the way back to the radio and into YOU the operator.

[@usernamemykel]

Between this KM4ACK, and the K6ARK, which has given you better performance? Thank you. 73 N4ANO

[@DonzLockz]

Nice, it would be great for pota. Nice and light and compact.

[@goku1205]

How many meters of wire does that antenna have?

[@CravenMoorhead_23]

I believe it's 67 feet long, so: 20.422 meters. Lance KJ7QDI

[@donaldsmith3048]

Doesn't it come with distructions? Can we put bigger wire so it can handle 100 watts?

[@HamRadioCrashCourse]

Yes and yes. Instructions are on the KM4ACK wesbite linked in the description.

[@thomasmaughan4798]

You also need a bigger toroid to avoid saturating the core. That's the main difference with the higher powered transformers.

[@seankidwell8447]

What is that device in the top right of the screen?

[@alebret3]

if i'm guessing correctly, that device is a nano VNA

[@lonewolfhamradio]

What is the length of the antenna wire ?

[@chesty1369]

67ft

[@kschildt1]

I use a long wire and a tuner. Works better than the end fed junk. No balun loss since there isn't one.

[@HamRadioCrashCourse]

I'd argue you're losing the same amount to heat with using a tuner.

[@kschildt1]

@@HamRadioCrashCourse When using the correct tuner, I use a L-network, the loss is negligible on all frequencies from 3MHz to 30MHz.

[@patring620]

@@kschildt1 Thanks for your opinion, Kenneth. It sure sounds like you have the perfect antenna set up, and the perfect tuner, too. I'm just surprised every ham radio operator in the world isn't using the same antenna set up as you!

[@thomasmaughan4798]

@@HamRadioCrashCourse "I'd argue you're losing the same amount to heat with using a tuner." You would argue but you know better ;-) It is the ferrite toroid that loses energy to heat. Air wound coils and capacitors in a typical tuner don't have ferrite and thus negligible losses. However, if the tuner uses ferrite cores (and many miniature tuners DO) then it would be about the same. The tuner has the obvious advantage of tuning antenna wires that are not exactly the right length OR whose wires, even if perfect length, are de-tuned because of nearby metal.

[@thomasmaughan4798]

@@patring620 "I'm just surprised every ham radio operator in the world isn't using the same antenna set up as you!" Most of them are. The "EFHW" is a fad; good for the somewnat usual circumstance of hilltopping, SOTA, things like that where you go somewhere, throw a wire in a tree and by the very nature of things you and your radio are at one end of the antenna. That is NOT an optimum scenario but sometimes that's what it is, and when it is, then a properly cut EFHW antenna and properly grounded UNUN works well enough. Note that no mention is made on this video of grounding the UNUN. Transformers ALWAYS have an instantaneous "in" and "out" for electrons; but we seem to ignore it in these cheap little designs; but it is THERE. The "counterpoise" or source for the actual antenna current is the outer shield of the feedline coax, and its source is YOU holding the microphone. Unless somewhere in this you thought to have an actual ground.

[@oncomics1128]

DX Commander made you happy, too? I like this one, I would put a second cap on there the deal with the rare but real double-pop. Good work, KM4ACK! Josh, did you settle on glue gun or tape considering the temp dips overnight?

[@oncomics1128]

Might also add a lightning cap and ground wire. I am a real chicken, I know.

[@45auto]

I realize that this an older video but be advised that when I tried the link to buy this antenna kit I received a 404 Page Not Found message.

[@CravenMoorhead_23]

It's fine today, but they're out of stock.

[@jaspatters1]

power rating?

[@HamRadioCrashCourse]

50w ssb 20w cw/digital.

[@lancewillard]

I have this antenna and it works phenomenally well. I set it up in a hybrid slope/inverted L configuration (approximately 30 feet high in the air, at a 75° angle, using a tree branch) with my Yaesu FT-818. From Central Texas, I have worked Missouri (613 mi), Georgia (794 mi) and Wyoming (848 mi) on the 40 meter band; Chicago (966 mi) on the 20 meter band; and West Virginia (1,290 mi) on the 15 meter band, ON FIVE WATTS. The antenna works QRP phone on multiple bands very, very well.

[@DP-np5mm]

Quick probably stupid rookie question...how are you able to reach these distances on these bands whereas GMRS (UHF) will only reach line of sight within so many miles. Is this just due to the different size of the inherent radio waves or is some other repeater or "link" being used?

[@andrewhamop6665]

@@DP-np5mm VHF and UHF are typically line of sight, where VHF can go slightly be on the horizon. HF however, uses the ionosphere as a giant mirror and can bounce signals hundreds or thousands of miles in the right conditions.

[@HarveySidney-r7o]

Hernandez Michael Gonzalez Brian Wilson David

[@RicSpivey]

Seeing you mess up fuzzy measurements is almost as entertaining as learning all the things! Love the channel

[@HamRadioCrashCourse]

Hah, thanks! Best to keep it easy with some of these antennas. No need to get too serious when we're just going to get it into tune in the field anyways :D

[@RicSpivey]

@@HamRadioCrashCourse it's totally in how you dealt with it, makes ALL your stuff chill and really easy to watch

[@HamRadioCrashCourse]

Thanks I appreciate that!

[@joeb3300]

It looks like you made THREE loops on the first attempt. But instructions would be helpful.

[@thomasmaughan4798]

Three loops is fine just remember the turns ratio is what matters. At low bands (80, 160) three turns on the primary is recommended.

[@wild-radio7373]

🤜🏻👍🤛🏻♡♡♡

[@antcri730]

$40 is a bit pricey for this.

[@patring620]

Of course it is! Why, everyone can order exactly one capacitor, exactly three feet of magnet wire, two ring terminals, a single toroid, a cool winder, heat shrink, a BNC or SO-239, some stretchy paracord stuff, stainless washers and wingnuts, and 70' of 20g wire. Even with shipping, I am sure it is a few dollars cheaper. Building one is always more expensive than building a 100.

[@jamesgeorge1709]

kind of a sloppy build, maybe you should have read the instructions.

[@HamRadioCrashCourse]

That was kind of the point how little could I go in with and it still work.