Відео

Here's a stupid question: how do mere mortals make a folded dipole?

Justin... Very interesting, especially the comment on the latest NEC being able to handle multiple bends. So can this better model Linear Loaded, Multiple Foldbacks on a Dipole on Lower HF Frequencies.?

Good advice, thank you. Yep, the wrong choke balun inductance or placement can actually even make things far worse. I use silver teflon coax wound #43 & #31 material toroid cores right at the feed point all over my own antenna farm mostly made of coax fed wire antennas.

Good to see Justin making YT videos.

Interesting stuff, I was never aware that the matching made the antenna unbalanced in that it affects the radiation pattern. I am experimenting using the small ladder line feeder, I think its 250 ohms, but the j pole calculator and my results don't seem to add up. A s all change in direction- I wondered if you have come across the Lambderhalbe antenna that is a J pole made out of coax and a half wave wire. I have one of these on the lower cb frequencies. It sat in a drawer for years until I realised that it had comparisons with the J pole. Top precise videos, I really like that.

Really informative videos Justin. I'd be interested in your opinion on the operation of the balun (1:1 choke ) type that is used for common mode current removal from the feed line I've seen it where a feed coax has toriods fitted close to the 50 ohm dipole feed point then 1/4 wave down the coax is a connector and it outer casing is grounded to the boom via a bracket at this point connection to the rest of the feed line. I can see from some explanations of how this works but i don't see yet how it does the transformation from balanced to unbalanced happen?

I recall a J-Pole was the very first antenna I used for 2m SWL before I had a license. It was on a piece of wood just outside my bedroom window, plugged into a Diawa SR-9 receiver. That was back in the early 1980s, when I would listen to the GB3WR repeater.

Cool

Good to see new recent videos from you, Justin, nice work, I follow your work for many years and built a lot of VHf LFAs, always worked very very well. Maybe you could help me with a question, I want to build a 4 element wire yagi for the 40 meter band. Do you think it could be possible to adapt an LFA design to use it with wire cable? I have been trying to model some antennas based on your designs but in my final results bandwidth is very narrow compared with adapted OWL/OWA designs. Could you give me some advice? Should I build a LFA or should I go with another designs for this big Uda Yagi? Thanks,.really enjoy

I've always considered them to be an end fed halfwave antenns with a rigid "ladder line" (I quote because no insulating rungs are needed) matching section shorted at the base, open at the top, and an impedance transforming feed point is designed to match to a coax cable. There is probably no reason the halfwave radiator has to be in line with the ladder line, and no reason it can't be folded midway to form an inverted L just as one can with any efhw antenna. The polarity of the radiated wave is then up to the installer. The ladder line matching section is used instead of an unun transformer that does the same impedance matching in a contemporary EFHW.

Hi Justin. I've heard from some people that a "Slim Jim" is not as good a a J pole. What are your thoughts on the Slim Jim and potential improvements? Perhaps in a next video? Regarding the remaining ripple in AC cancellations if the feed-line or radiating elements had more capacitive function in their design, weather it be to smooth out ripple or to match impedance could this be a bonus when it comes to cancelling ripple? More capacitive function in general whenever possible if your trying to smooth ripple? You set me off when you mentioned Sigma IV. I Had two beautiful originals and my father threw them out! So are you saying a J-Pole is always going to be a 1/2 wave and it can't be scaled up to 5/8 or 7/8th wave? The problem with all this antenna simulation is that there are almost always surrounding objects and masts, coax etc.

I like your adjustment method! I wasn't aware adding the down lead pulled radiation down, nice! I see a J Pole working as you described. A few points to aid understanding. If I short the bottom end, the top end will have a very high impedance (transmission line transformer). That is needed because you need a high impedance (high voltage, low current) to end feed a 1/2 wavelength. Assuming the 1/2 wave impedance is 2000 ohms, an impedance of 316 ohms is suggested (SQRT(50 X 2000)). That is achieved when the center to center spacing of the transmission line is 7 times the wire diameter. How critical 1/4 wavelength transmission line the 316 ohms impedance is, I don't know. Some time with the model will predict how sensitive that parameter is. I would think rotating the matching network 90 degrees and adding another 1/2 wave to the unused transmission line end would narrow the radiation pattern, improving gain.

Very interesting. Having built many over the years nice to understand better the theory of operation. Thanks Justin and look forward to seeing the build of the antenna.

That balun solution being tuned (cut) to some specific frequency, doesn’t shorten the bandwidth of the antenna? Regards

One of my experiences is that self-vulcanizing rubber tape acts as a conductor for high frequencies. Most notable when it comes to VHF and up in frequency and it can definitely kill the output of an UHF antenna. How about a current balun - can that be used to avoid having a choke balun?

I did like the diddlie om Pom Pom of the big trombone antenna.

Hi, thanks for videos, i learn a lot LA7PSA. I see that his (KB9VBR) antennas do not stop at hairpin and he uses pipe as a mount. Will this do the same as your suggestion? And what du you think of his explanation on slim jim for same purpose? ua-cam.com/video/Uwbu76mvs2Y/v-deo.html

Thanks Justin Suggestion for the follow up video for this great explanation: How do you go about designing the J-Pole antenna from scratch and tuning it. Lest's take a 70cm antenna; Software model design and optimisation; Choose of material and diameter of elements; Build, tune and compare against model. What techniques would you use to tune an antenna of multiple elements like the J-pole? What analyses / test equipment would you use?

Keying on the least important bits, I'll keep my towels short and always have tea.

Excellent again, Justin; many thanks. Great to see someone who really knows what he is talking about when it comes to antennas....and busting the myths swirling around on UA-cam etc! 😄

Outstanding video. Very deep. I have watched many j-pole videos and they do not cover what you did. You have excellent communication skills. I make J-poles for 100mhz. LPFM we are limited to 30w max by the government here. we only use 15w on our solar repeaters. SO antenna efficiency is very important. On that down radiator, what would the approx length be at 100 mhz? Please do more on the J-pole. I am using 2 element and 3 element in my design. I use a folded phasing line because as you said, the coils are very difficult. I have spent hundreds of hours on these but I don't have the tools you do. Just an SWR meter and a testing range. Thank you again from the Philippines.

Don't make things complicated if they are noth. It's nothing more than a half wave dipole. And eznec don't handels the 1/4 wave transformer correct.. The 1/4 wave tranformer is noth a part off the radiater ;)

Thanks, justin for all your guidance. It has been long awaited. Things that you say confirm my beliefs and experience. You say about the testing of common mode after you’ve built the ugly balun. Sometimes this or probably most times will not show itself to be evident so the test is a bit like keeping your fingers crossed. How do you get over that? I always put an ugly ballon on but I have since land they are too far away from The driving element but placed comfortably for the coax to run and ideally I would use messy & paloney 7.

Justin, assuming that the right correction factor is applied to the elements, is there any advantage/disadvantage in using a fiberglass boom instead of a metallic boom in a through-boom design?

As highlighted at the end of the video, make sure the coax's braid is NOT touching the stub braid otherwise everything is shorted, and you will never get any resonance. This happened at S9Z, and we lost one moon pass before fixing it.

Thanks for the vid mate!

just subbed

Thanks for the presentation. I found a lot of reliably tested information at sites like Palomar Engineers, Balun Designs, DX Engineering, etc. These folks have the finished units, the DIY components AND (and this is key) the test data to back up their designs.

Thanks for this Justin, you give all the information that is needed and none that isn’t, in a clear and straightforward way, well done! I look forward with great interest to your future videos.

All useful stuff to know and understand, do you have any thoughts on the 1/4 wave half loop trick as once presented by Mark Tonna? as described by G4CQM on his website.

Great video looking forward to the j pole 73

Thanks, Justin, for a great video! I have a question about older designs like the MA5B (a compact 2-element Yagi on 10m, 15m, and 20m, with a shared element acting as a rotatable dipole on 12m and 17m). On this antenna, two short tails, approximately 40 cm each, are zip-tied to the boom, connecting both the Yagi elements and the dipole to a shared matching network (on the cold side). The balun is housed in a plastic box directly attached to the boom, just millimetres away from it. Could this close proximity to the boom impact performance or introduce issues? Would it be beneficial to move the balun further away and add ferrite beads to those tails?

Thanks for this video Justin. This got interesting to me at about 16.30 because I'd always wondered where to place my ferrite rings, at the feed point, or six inches or a foot below. I have mine a foot below and this explains why my dipoles are much shorter than I expected. The technical radio books don't explain and just say use a choke. At the feed point does make sense. I also find there is still r.f. on the coax which I imagine is r.f. picked up after the choke so I put another ferrite ring a couple of feet from the tx..There's a lot of r.f. in my attic to be picked up on the other four dipoles and down the other coax, five dipoles for 20m to 10m fed with two coax cables. I think we need ferrite sheathed coax included in the braid. Maybe a number of clip on ferrite beads spaced down the coax would work. G4GHB.

Execellent video...... The number of times I've seen an Ugly Balun cable tied side on to the boom... I just shake my head. A couple of things..... What if the boom is something non metallic? Can it then be cable tied side on? What about if it's still metallic.... can you mount the Ugly so the TXer side (the side going to the shack) is closest to the boom? This would have the aerial side away from the boom. Not ideal as then coax needs to come back to the connection point. But the majority of the Ugly is not near the metal boom. I've always wound my Ugly Baluns on the likes of 110mm OD PVC pipe. 16 turns of RG213 gets a bit large and heavy. If used on the ground with a vertical I cut the pipe so there is about 200mm left after the winds stop. So it can be fixed to a wooden stake for support or surronded by house bricks to hold it. Used in the air I normally cut the pipe just a little longer and and fix with an angle bracke to the boom. There is about 50 - 70mm between the top wind of the ugly and the boom. If it's an aerial like an Inverted V it just gets a bit of rope set up to hang it. 73's from VK2

Thanks for this video, I hadn't considered the points you raise and was glad of the information. I have some antenna fed mods to do!

Excellent, very informative. Looking forward to the j pole video👍 73 Kevan 2E0WMG

Great explanation, made absolute sense when you showed it like this.. Thank you Ricky G0LZX

Brilliant explanation Justin and the last couple of videos has opened my eyes with regards feeding my yagi correctly!! How do I work out how many turns required for my 4el monoband yagi? Thanks for your time.73s

Great explanation of why a correct choke/Balun is needed for a beam.I now know why I’ve been a little disappointed with my 11m yagi performance!! Looking forward to the next 1 regards placement of the Balun.73s Chris

All good Justin, what's the whine in the background?

And an "Excellent" from me to Justin. Good job mate. I will recommend this in the baluns and antenna groups. 73 Rick, DJ0IP

Justin, could you cover bead-baluns at some point? I've been using self made ones now for many years. Mostly by guessing. It would be nice to get your perspective on these, and how best to arrange them ref. the boom. I imagine similarly (UNDER the boom, at an arc away from it, and then the coax back to the boom. But I'd love to hear your thoughts in a similar forum as this.

Thank you for the explanation on how to do chokes correctly. You said to ask questions, this is not quite related to particular video. But maybe you know what tricks are used in antennas like OB17-4 / GXP 17-4 / AD-3334 to make 40 and 15m bands play along reasonably well. I know its similar to your 2m/70cm video, but here they make them work fairly well judging by F/B and gain. From what I notice they seem to use different tricks: - some use dual cables, different Zo for the 40m band - all of them use traps on 40m (I start to suspect its not only due to size?) - 20-15-10m are fed directly, open sleeve is not used (?) what am I missing here?

And another one! Woah. Good work mate.