Make a 20 & 40m linked dipole (and get 15m for free!)
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- čas přidán 25. 11. 2021
- I make up a linked dipole for 40m and 20m. Then, I add small air cored 1.1 microHenry inductors at the links to make it resonate on the 15m band, as a 3/2 wavelength antenna. This is a great solution for homebrew or kit rigs that do not have an inbuilt tuner and need a naturally resonant antenna on all bands.
SOTABeams post on modelling and options for getting a 40m dipole to resonate on 15m:
/ 486347494855297 - Věda a technologie
Neat! I did a similar experiment with using 40m dipole on a 15m band some time ago, but instead of phasing coils I used "butterfly" capacitance hats. The technique is well described in the article "Antenna Here is a Dipole" written by James Hearly, NJ2L, and published in QST for June 1991. It's easy to find. The advantage of using capacitance hats is that the losses are less than in the case of coils. But they should be placed at ~1/3 of the length of a 40m dipole, which wouldn't be convenient for this project.
Hi Alex, thanks again for commenting, you always shine some light on the topics of my videos. I Just added the Facebook URL for the SOTABeams post on making a 40m dipole resonant on 15m. They do suggest 'capacitance hat' wires of a few metres connected at the 20/40 link and left to drop vertically. This apparently brings the resonance down but other factors inhibit a lower SWR. The best option, they advise, is the 1.1uH inductance in the links.
Curt Stacy in another comment suggests connecting both the 20m and 40m dipoles at the centre, giving a fan dipole. This apparently resonates on 40 and 20 as expected, also 15 and 10, presumably by virtue of the dipoles each working at 3/2 lambda on these higher bands. May be a bit of a wire tange on a summit, but worth trying sometime. 73 Paul VK3HN.
@@Paul_VK3HN The reason why I'm commenting is that you are publishing such great technical no-BS videos, Paul. This is rare on CZcams these days :) Thanks for doing this and keep going!
I can confirm that 20/40m fan dipole has SWR < 2 on 15m when fed with a λ/2 balanced line with account for velocity factor on 40m (i.e. half-wave impedance repeater @ 40, full-wave impedance repeater @ 20). According to my notes, it didn't work with a coax, but maybe I just didn't check that it did. It did work with a 20/40m fan vertical ("fork antenna" as we call it in Russia, "carrot antenna" if it has 4+ bands).
Another good option for SOTA can be a ZS6BKW antenna for 40,20,17,12 and 10 meters (FM part of it). The traditional design described in most sources implies a specific height of the mast and dipole (flat) shape of the antenna, but I recalculated it for the inverted-V shape and the height about 10 meters above the ground. The details can be found in my blog. ZS6BKW can also be tuned to 80/30/15 meters using a tuner as G5RV.
Great solution! Wire antennas are great for portable stations - very light weight. My first HF antenna project was a linked dipole for 40,20,17,15 using 3 sets of links. I am pleased with its performance. Thanks for the video and 73 de Brian - K3ES
Thanks for sharing Brian. I used a linked dipole, 40, 30, and 20 for about 5 years, a very reliable and simple antenna. You do have to drop the ends to open/close links but I do not generally band hop a lot, so it doesn't bother me too much. All of my SOTA rigs are homebrew so I do not carry a tuner. Hence native resonance is essential. I've never tried this loading of a 40m diupole to getit onto 15m but it worked as describved. Other commenters have suggested several alternative schemes. And welcome to ham radio, portable operating and hopefully soon, CW, the ideal portable and parks mode!
Paul, Nice video. If you can handle a little more weight on the mast try a 20m dipole soldered to the same points as the 40m. keep them about 6" apart minimum. can go a lot farther apart.
then you have the fan dipole or the maypole depending on where you rotate the elements. this will give you 40, 20, 15, 10. being the fan type dipole it will make it more broadband and you need no jumper or coil. this is a nice way because there is no need to pull it back down.
Curt, thanks, a fan dipole with 20m and 40m elements is a very good option. If you noticed in the video, I made up each wire element with a spade lug at the centre end, which hooks onto the centre-piece (made from old PCB). This arrangement would make it possible to use just the 20m wires, just the 40m wires, or both. I agree that dropping the ends to open/close links to move bands is not ideal, but it has not worried me too much to date. I must try your suggestion next. 73 Paul VK3HN.
@@Paul_VK3HN I didn't notice that Paul that is a good idea to keep it changeable for a mobile antenna. just put up what you need. I will need to try that with my Spiderbeam for fieldwork. Any suggestion on wire type for the weight?
The current configuration I use just for a note is permanent with an 80, 40, and 20 it is truly amazing 2:1 and below on everything but 30 meters. I have a 1:1 balun and 100' of RG8X.
A good result. I was always wondering if the observation tower was still up on Mt. Donna-Buang, and I notice from your video that it still is. Last time I was there was in the 1970's. There was a similar one here in central Gippsland, but it was removed. I've contemplated taking a few clamps and a pole to take advantage of the structure to operate from. I can imagine it's a popular place for Sota.
Its one of the most activated SOTA summits in VK3, because it is just an hours drive from Melbourne, and the road is sealed and excellent driving. As well, the lookout tower and no Comms Facility so it's RF silent. If you have some gear to use portable, even a VHF UHF hand held, and you are in the vicinity, well worth a visit.
@@Paul_VK3HN Thanks Paul. I'm in Morwell, so it's a fair hike for me, but I can see myself visiting there with the wife and the go kit. I recently travelled the road from Launching Place that goes over the top and heads down to Healesville. There is a turn-off on the spur that heads to Donna Buang but that road was closed. I imagine the best way there is via Warburton.
Cheers, John.
1w SSB to ZL …. I got excited too!
That's an achievement!
Brilliant
Thanks!
Hi, great video thank you. I tried this and I have 20 and 40 fine but can't get 15, in the video you say 11 turns on 20mm tube but the picture shows around 6 turns, can you please confirm?
Also, you call it an inductor, but without a toroid, is this not just a resistor? Sorry, can you please clarify this part of the video. Thank you.
Hi, you are correct in noticing the discrepancy, the hand drawn picture shows 11 turns, but the finished inductors show about 8 turns. I think I can recall starting with 11 and finding the actual inductance as measured on my LC meter was too high, so I took 3 turns off. You need around 1.1uH. The actual inductance may vary in an air cored coil due to wire gauge, tightness of the windings, and former material. Just aim for 1.1uH. I should have explained that in the video!
Good luck and good DX on 15. 73 Paul VK3HN.
@@bluebellsunseeker1167 Not all inductors are wound on ferrite, or powdered iron. This one is 'air cored'. Google it for the theory and some cool examples. They are widely used in antennas, power amplifier stages and matching units where RF power flows.
With the measurements being fairly precise, 5m and 5.1m, when you have the cable going through the board, knots, etc. are these taken into consideration? Is the length in total, right up the connector? This looks exactly what I need but as a complete novice would like to make sure, thank you.
Measure the sections from the extremities, ignoring the wire tails that wrap back on itself or thread thru brackets, these should have little effect. At HF, 10 cm is not that significant. I think Callum M0MCX has a short video on this question on DX Commander channel. You might enjoy some of his videos, he explains things very well. Good luck!
@@Paul_VK3HN Thank you Paul, appreciate your reply. I was concerned only because the 2 measurements mentioned were so specific with only 1cm between them.
@@andyzot Its 0.1 metre, 10cm, or 100mm. So the 20m legs are 5m, the 40m tails are 5.1m. You know what they say about making antennas? Measure twice, cut once! Good luck.
Hope all is well. Any new video comming soon?
Hi Praveen, have been busy with other things lately, thanks for checking in!
Great video Paul thanks for sharing de 2e0ree
Glad you enjoyed it.
Yes just as long as the CW end has good SWR …. All that matters! 😜Thanks for this …. Much to my XYL’s horror new antennas are afoot. I like the linking method! 73 de VK2AOE.
Thanks George. I prefer resonant antennas on all the bands I operate on. That's because I use homemade rigs with no inbuilt ATU! But also because I trust them to be efficient. Good luck with your experimenting.