Building a Short 40m Antenna With Coil and AT-271 Whip.
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- čas přidán 11. 12. 2021
- Things did not work as expected with this great design by VA3TNE on Thingiverse. The coil is used with an AT-271 military antenna whip, 3D printed and tested here with my TRC-372 manpack radio at the Col de Vence North of Nice. Maybe someone more experienced with coils could shed some light on the issue...
STL 3D files: www.thingiverse.com/thing:235...
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Thank you for showing the good and the bad
You should use a hot hair dryer for the heat shrink to do it the right way.
21:09 "Past failures are the _breeding grounds_ for success!" - Me
Hilarious ft8 joke at the end there Gil ... who knew ham standup was a thing. Love your videos !
Happy Printing, Gil. *H I* Thanks for that vid and a happy week! 73, Jan / Germany
Enjoy your videos. I hope you continue to work with the coils. I always learn something
I will!
I enjoy your videos...real people experiencing real problems! It was obviously getting colder. Anyway, I made a coil14" in length and 1.5" in width. I used bare wire and a clip to adjust the tuning. I can get a low SWR down to 80 meters with a counterpoise, but I have to hit the exact spot on the coil.. The coil's ugly but it works. Your video is helpful, and it's encouraging to see that others have encountered the same issues that I have. Keep up the good work.
A clip is the key!
Maybe check that the impedance is correct using a VNA. I see that the designer suggests using 16 gauge galvanised fence wire. American 16 gauge is about 1.3mm diameter and fence wire is iron not copper. I’m not sure how much difference that would make.
It might indeed...
Did you test the filament you printed your coil form out of? not all plastics are compatible with RF.. to check it just print a token item out of the filament and put it in the microwave oven along with about 8 oz (a teacup) of water) and heat the water to boiling (212 F, 100 C) and check the token item for heating from being microwaved. If it did heat, it will affect the impedance of the coil wound on any form made from it. We have been using this method to test any plastic forms (Discarded deodorant dispensers, pill bottles and so on) for decades an inert plastic will NOT heat up in the microwave oven, and the cup of water is needed to act like a dummy load to the oven..
Scott N9TGW
Interesting thanks!
Interesting idea, will try it with different materials!
Brilliant, simple test, thank you.
Outstanding point!!
Interesting nugget of information. Ill log that in my knowledge database for future use. Thanks.
Salut Gil, pour faire de la gaine thermo rétractable de gros diamètre, tu peux utiliser des bouteilles d’eau plastique, ça fonctionne bien 😉
... all the work is done ... now you can look towards mass production 👍surprising results at the end of your radio.
No mass production, LOL!
@@RadioPrepper Absolutely! With this amount of printing time. And coils are very narrow.
But with every new test we get better experience 😉
I'll try an adjustable one...
@@RadioPrepper so I'm already curious! Have good ideas for your planning 😉
Looking for coils on Thingiverse...
Belle radio, félicitations et j'apprécie vraiment votre contribution... XESWL-3017 du Mexique 73
Thanks Gil. Great video.
👍
I used the larger coil with steel wire from eveks ev_edelstahldraht-1.4404-1.2_5
Connect one side to top screw, tho other screw is connected via a wire to a slider.
Works great on 10-40m with a at 271 whip and some radials
Nice video, the best way to learn is through experimentation trail and error, I use to be a professional PRC320 and VRC321 operator, there were days coils were great and other days whips without coils, then tune the best match, sometimes which might be to the first mark on the dial (very bad match), then you the best audio filter; the one in between your ears to establish global comms, keep up the good work 👍
Will do thanks!
3D printing has to be one of the most useful innovations of the last 50 years and can be the answer to everything from making one of bespoke parts to replacing rare and obsolete items.👍 When they become a bit more affordable I'll be shopping for one!😀 In the meantime I made a coil for 40m from some 110mm white plastic waste pipe, some 1.2mm ECW, some bits of aluminium and steel tubing and a few nuts and bolts, all of which I already had lying around so cost me nothing. I use it with a 5.2m telescopic whip, similar to the MFJ items but a Chinese copy for £23. The coils screws into a 600mm long, 25mm dia aluminium stake via an earthed steel mount and in soft moist ground it works great without the need for radials although it has the provision to connect some if required. It tunes well from 40 to 10m.👍😀❤ I like those military handsets and thinking of getting one to modify and use with my TX-500.
Nice. I will be reviewing a new printer in a few days..
Well trial and error as me and a friend always say , great video as always 73s from KI4RBF .👍🏻
Hi Gil, always a good day when I see that you’ve posted a video.
When running any vertical especially quarter wave verticals your radials are as important as the vertical itself. I would recommend a minimum of four. And more would be even be better with the diminishing returns after you get above 16. If you can’t get full length 1/4 radials, many short radials is better than a few long radials. This is because the return currents are higher at the base of the antenna.
As the antenna length drops, the feed point radiation resistance drops making it very challenging to get the RF energy into the antenna system. You can think of it as series circuit with the combination of the radiation resistance, ohmic resistance in the antenna conductors, and the ground resistance combined. Having a good radial system allows the RF energy to be focused on the radiation resistance and not the ground loss. The Ohmic loss in the antenna are usually a smaller factor, but as the radiating element gets smaller and smaller they can come in to play as a concern. The radiation resistance is where the real work is done, so you want it to be the predominant resistance the transmitter sees.
I think your coil will work fine, but you need to fix your radial system first.
73, de KB7ZUT
Thanks, I will make a portable radial system...
@@RadioPrepper Gil, good stuff. I’m traveling this week, but when I get back to my office, I will send you a couple of documents with the details. Not too technical, but full of good info on optimization of verticals and radials. It could be a topic for an upcoming video to share with your viewers. 73, and keep making this awesome content.
Awesome thanks:-)
Good video❗️I thank a lot of the old military Radios were designed with internal antenna tuners that were able to tune to many different antennas for the same frequency to allow for damage to the antenna in bad field operations. If your existing antenna was damaged just patch it retune and go❗️👍 73. KV5P
Indeed, great radios!
When you need to cover such big coils, pet bottles can be a good option.
If the resonance frequency was at 9.3 MHz, the whip is too small and needs to be lenghted for 7 MHz.
Best to use an adjustable coil with a slider (JPC-7) or plug (Buddistick) in order to adjust inductance to bring the antenna into resonance.
Furthermore, a counterpoise (either at least one elevated and tuned radial, or as many as practical untuned ground radials) is really required with this type of antenna (Groundplane) in order to perform well and bring SWR down near 50 Ohms.
As pointed out by you, placing the coil higher above ground increases the efficiency of the antenna system when transmitting.
Great job done with your 3-D printing!
73 de Chris. DL1GKC
Thanks, I'll try an adjustable one..
Hi Gil
Great 3D printing project. Tapping the coil will be more successful as it will make it tuneable, you would be able to primarily tune it using the receiver audio. Also the black plastic may be causing you a problem.
I built a 2m J Pole using black conduit and it was a nightmare to tune as the black conduit was acting on the aerial, the second one using white conduit was perfect first time.
Good luck and have a great 2023
Interesting thanks.
That is probably due to the carbon content used to colour the plastic and also provide some UV protection.
Thank you....very interesting 👍🙂
1:57 A ground banana?🍌😜😅
A good vid Gil, have you checked the resistance in your coil? What is the pico farad rating? How many turns are required? It works well on reception though. All the best, 73
I haven't measured anything yet because I finished it the morning of the test..
I think it is expected to have a very narrow bandwidth with a heavily coil loaded antenna, and that it is quite unstable if you change counterpoise position. You should try and hook up that coil to a end fed wire, maybe it can go to lower frequencies. Maybe you could use a plastic water pipe and print only a few (3-4) "coil former" stripes, flat on one side (for gluing to the pipe) and comblike on the other for guiding the wire. I saw a youtuber do that when making a coil for a tuner, haven't tried it yet myself.
That would be interesting...
U could have tapped the coil like the buddiestick it’s what I do with the cha mil setup using a tapped base coil nice job on the printing now I want a 3d printer Thankyou and look forward to your adventures
Thanks, indeed, I used to own a Buddystick, good antenna.
Cheers n keep warm Gil!! Reminds me when Thomson CSF made Airbus Flight Simulators,.. 73
No idea they did!
With taps, and the 5m whip u can use it as a vertical for 40m. I have recently done this, and btw your coil looks very rugged!!
I'll try thanks.
I operate a QCX-Mini powered by a 6ah LiFePO4 battery with a Wolf River Coils Silver Bullet 1000 with six 32' radials on 40M. I live in Arizona and get 3 or 4 state propagation. I loved that you printed that purpose built 40M coil. I'm not sure that the coil is no good maybe just the application. You should try it on a QRP (or just a simple radio without the ATU) radio with a simple vertical and counterpoise. I think it might work. Great video, stay warm.
73
That's a huge battery for a QCX!
Would be interesting to see your coil and whip combined with a radio without a built-in ATU. I'm just wondering if the coil/counterpoise set up was too much for the radio's ATU to match?
Interesting, I should try..
Gil, I suspect you are correct that the Thomson radio's matching system allows the short whip to radiate more efficiently. The internal matching output will be at the whip feedpoint. So, when you add the coil, it is just adding a non-radiating load at the base of the whip. Not only that, the RF current will be at a maximum at the base of the whip (where the coil is). So, it will be best not to use any coil, so long as you can get a match with the radio's internal matching.
The 6:1 VSWR, I am not sure about. If the analyser was calibrated with a 50 Ohm resistance, it must mean that around the miminimum VSWR, the antenna is just not 50 Ohms resistive. If you plot the impedance across a frequency range, you might find the antenna has a purely resistive resonant frequency that is not 50 Ohms?
Right, who knows.. I will just use the radio's tuner now but might tinker with the coil a bit more...
I enjoy watching your videos as you learn more and more about RF. That's what ham radio is all about, or should be.
Here's a long-winded comment, I'm afraid. Some Elmering if you want it.
Unless you can do all of the calculations for it in advance, (some substantial math,) feeding a tunable circuit (the rig's output,) into another tuned circuit (the coil's inductance and its capacitance) is just gambling. Your radio's internal tuning circuit is already designed to tune a short whip, but the loading coil makes it appear to be a full-sized whip, sort of. And a physically short antenna with a big loading coil will ALWAYS be narrow band. That is why they have those little alligator clip jumpers you mentioned for fine tuning.
Basically, you want to look at the entire output circuitry and null out the reactances, and hopefully leave yourself with the output amp stage seeing the resistance it's designed for, but you have added unexpected reactances due to the coil. If you had a rig without an output tuning stage, simply one preset for 50 Ohms like many commercial rigs, then your whip and loading coil might work fine, perhaps needing a counterpoise wire or 2, or a good ground. But you would still need to be able to fine tune the antenna loading coil since it would only cover a narrow bandwidth, depending on its 'Q', and the better the Q the narrower the bandwidth. It's a tradeoff in efficiency and bandwidth that is best solved by being able to fine tune the loading coil if you want maximum signal.
But here's where I suspect the problem lies:
Did you hook up some counterpoise wires and run the whip on an antenna tester or a NanoVNA? That will allow you to see what's going on with your antenna, and where that LC is actually tuned for. I'm thinking you will find its entire narrow bandwidth to fall below the 40 meter band due to the loading coil capacitance. Plastics are only 'inert' to DC. At RF they become an active part of what's happening. Depending on the type of plastic you used for the loading coil form the coil's self-capacitance could have put its relatively narrow tuning range completely outside the 40 meter band leaving the coil to act like a trap on 40 meters. Note that the resonant frequency is a function of the whip, the loading coil's inductance, AND the loading coil's capacitance. The capacitance of a loading coil is due to the proximity between each of the windings, AND any plastic form (a dielectric material, like plastic, that you wind it on increases that inter-winding capacitance substantially, to a degree based on the type of plastic used. That's why you will see old radio coils made of ceramics. They have very low capacitance. And you will see capacitors made with a wide variety of dielectric plastics because each type is different in its electrical properties, each with advantages and disadvantages.
BTW, don't be fooled by the fact that you could hear some stations on that antenna. A rig's receiver is designed to receive stations over a dynamic range difference of many thousands of times. Your antenna can be utterly miserable and still receive some strong stations. But an antenna that is cutting your transmitter power by thousands of times leaves you with essentially nothing.
Thanks. I was indeed hoping that it would end up being "close enough," wishful thinking... I tried a single 10m counterpoise wire which I rolled up while testing the SWR. I should have done a wider sweep with my analyser.. I'll probably make one with the alligator clip so I can use it on multiple bands...
It is counterintuitive, but this 3D printed adapter will be stronger if printed standing on its brim, rather than on the large flat face. The print is stronger when largest stress is parallel to the layers. Thanks for your very instructive videos.
Indeed thanks!
Hey Gil... Thanks for this video... I have been trying to utilize my AT-271 whip antenna. I will give your solution a try.
73! Tim, DK8MT
Keep in mind it did not work...
I often use a 6m vertical with a center coil and ATU at the bottom and of course a counterpoise. Works well on 80m and should work well on 40m as well depending on the coil inductance.
Dis you measure the coil' s inductance?
Not yet. What are tour coil specs?
@@RadioPrepper My short 6m vertical for 80m had a center coil of abt 60 uH. The coil was close wound with 1mm2 enamelled wire on a 32mm PVC tube, about 90 turns.
On the ground side I tuned the antenna with a small rollerinductor or with a FRI match (z-match) and used a few ground wires as a counterpoise.
I did the same with a 10m long 80m vertical. There the centre coil was 20 uH. For the 40m meter band the coil vallue is much less of course. I never tried that. Nice project doe next summer
Great info thanks!
Could you stack speaker voice coils to get the antanner the right length?
Might be worth a try, but finding the right value might be hard without regular taps to measure..
The whip you have is good, now just add a 14 Turn copper wire on toroid (your choice of power ) tap coax and whip into it for resonance, it will easily do 40m
@@brad1367 no Brad, wind 14 turns 1.2mm copper wire on your toroid leave an eye to solder on every turn, one end is braid the other is feedpoint (antenna), tap the inner coax at a point where it reflexs 1:1 +_
the braid connection can be moved closer(meaning 12 turns total or 11 or 10 etc...) or 7 turns as the freq of operation will change the amount of inductance we need, on a 108" whip 14 turns work like a charm on 7mhz.
i use a crocodile clip on the feed coax and tap into the toroid connections, for the different bands, when done ... i use a small bandswitch for quick change... When you use 2 mobile antennas (identical) in a dipole configuration, (portable, turnable dipole) you can use the same feed method via the 14 turn toroid, it makes for a small dirty tuner and feedpoint match. Hope you understand.
that such a mystery ! if you work it out please let us know 73s
Hello Gil
I have a 1970’s era Portuguese HF mil radio that uses those foldable antennas and they are quite nice for portable use (even with other radios). To an extent that when you mentioned “this one is a copy” you had my attention. Who is making those? I think the one i have is made in france (back in the day)
Edit: it is right there on the sticker attached to the bottom of it.. i found it! Looks great but priceyish and to me on the wrong side of the pond.. pitty
Cheers
CT7AXA
There are Chinese copies on EBay or AliExpress.
Do using a coil gets nice SWR but power loss on the coil when compared to a whip length for the 40 meters?
A coil should be better than a tuner. Coil in the middle is best..
@@RadioPrepper Thanks.
Just realised this post is two years old, I was going to suggest removing the red heat shrink altogether and re testing! What was your conclusion two years on please? M0KTY
Well. I used the wire for something else..
Sault Gil!
Did you test the antenna with your friend holding it? They will have reined it possibly.
Hi, no.
Your coil looks similar to the Buddipole 40 meter coil but without the shorting lead. It is designed to be used with a 5.5 ft adjustable whip plus 2 each 11 inch aluminum accessory antenna connecting arms. Max length above the coil is about 2.25 meters. Designed to operate 40-6 meters. I think that you may have a good coil that only needs some modification (a shorting lead to raise/lower the inductance) plus a reduced antenna length (your whip or other adjustable whip). Good video! 73 de AE5ZX
Thanks, I will work on it...
@@RadioPrepper I forgot one other attribute about the Buddipole 40 meter coil. Configured as a Buddistick (a coil loaded vertical antenna), you can insert the coil above the two 11 inch aluminum arms and then connect the 5.5 ft whip to it, so it would not technically operate as a bottom loaded coil (not the best location as you have so indicated), but sort of like a center loaded coil, but not really in the center. Is there some way you can measure the inductance of your homebrewed coil to see if it is suitable for 40 meters and above operation?
A fiendvof m8ne can, soon... I used to own a Buddystick...
@@RadioPrepper I still have my Buddystick. I am not all that impressed with it, especially on 40 meters. I am an end fed and random wire antenna fan for portable operations. Of course I know that your favorite antenna for portable operations is a real EFHW.
Indeed, but mine worked fine down to 30m... 40, not so much..
Hi . Just a question. Are you having problems with coax cable. I've have had problems due to cables being made of steel . Yes copper coated steel wire. Test with a magnet. I thought RG spec cables were copper or they used to be 20 years ago. Inner core breaking etc. Cheers from old George
Hi, I am not using any coax cable for this antenna. The coil plugs in directly into the radio..
@@RadioPrepper Have you tried a magnet on any of your coax cables to see if they are steel wires. ? Cheers from George
No, I'll try...
Here's a TIP for the heatshrink tube, Boil your kettle or a saucepan and steam the heat shrink
tubing for a much neater job.
Great tip thanks!
@@RadioPrepper Gil, recommend getting a heat gun. They are modestly priced and work exceptionally well. Do NOT settle for a hair dryer as they are too weak. I am surprised you did not opt for a shorting clip device - a la the Wolf River Coils antenna system - as that will makes the matching more flexible.
Regards, William, k6whp
Yes, I will get one, and will print a longer coil with a clip..
maybe the coil will help if it is in centre of your vertical part of the antenna.
It definitely would..
Hi friend, 73/51 of PY2SNN !
Thank you for your vídeos!
Very interesting !!! We love our glue !!! hi hi
It there a coil built in the radio ???
Yes.
I think you need to make the coil adjustable before you heat shrink it.
Next one ;-)
Attention, la température max sur ton imprimante est 240°C. Le PLA+ s'imprime à 220 environ. 270, c'est beaucoup trop chaud !
J'ai corrigé avant d'imprimer!
OK 👌 73s QRO
Just an idea, probably the material of the coil is making some interference with the antenna..just a thought
Thanks, it has been suggested...
Gil. Use a hair drier on the heat shrink not a flame.
I will get a SMT hot air station...
great video thanks 73 from kb2uew
Bonjour Gilles je voudrais savoir la longueur exacte total avec les bras de l’antenne s’il te plaît je te remercie d’avance
Bonjour, 2m85 si je me souviens bien..
Merci bonne journée
73 de CN8GFH
Check the plastic. First test put it in a microwave oven and see if it gets warm..... usually coils are air core.
Will do, thanks!
Hi. I am here because I am trying to figure out how my 40 year old mag mount CB ariel works. I've fixed it ... but still don't under stand how it works. I asked my Dad who knows everything about radio and didn't understand what he said. I am no idiot, except in his shadow ha ha. So my antennae has a similar coil, much smaller and is located in the actual base, nice, only the 6ft whip protrudes easily unscrews. Shouldn't your coil have a tap off it to tune the SWR? Like your toroidal experiments. I think they are called buddy taps in the US, they can be permanent or movable on the coil so the ariel can be tuned? My Dad tried to explain to me that the coil works as a transformer? If this helps great, if it doesn't I won't be offended ha ha because I don't really understand RF myself. I just measured what Dad told me (he is 90) and soldered and instantly got 1.1 - 1.3 SWR back on my very old mag mount. The coil is wound around a nylon former, I think the coating on the copper is cracking due to age and touching the nylon, I know that nylon absorbs moisture and expands and contracts and gets conductive, which is probably the cause after 40 years outside in the rain. The only thing I can find that describes this is here : czcams.com/video/EzaLdfcPOyI/video.html
Great videos, love your DIY!
Hi, yes, I will build another one with a tap.. Your 1:1.3 SWR is very good. If you have any question I will answer to the best of my knowledge..
süperrrrr..türkiyeden 73 ta7tac qrz
Sometime we spend a lot of time on something that ends up in the f--k it bucket. 🖐🏻73's🎙🎧 KD9OAM 📻
Yep, I'll investigate that one a bit more though..
Un peu court ton antenne pour trafiquer sur la bande des 40 mètres. La propagation est très bonne en fin d'après midi en ce mois d'août sur 20 mètres pour contacter la French Riviera. Je me trouve entre 14.122 fréquence d'appel et le 14.130 MHZ avec mon FT 817 et mon antenne NVIS. 73 cher om Gilles de Gérard F5MOX qrp à Paris
Je serais peut être en fréquence ce eeek-end :-)
Dump the HAT kg6mn
Great job!!! 73!!! de 4Z5KR