Ham Radio Antennas - Rebuilding the L network QRP antenna tuner

[@peterfenwick2540]

Hi Kevin, just a note to send my appreciation. Being the complete "everything has to be perfect" kinda nerd when it comes to amateur radio and after spending so much time with RF coil online calculators I realised I needed to follow your lead and just relax and make a simple damn coil and not worry about all the formulas. I had your videos in mind when I cobbled together coil number 3 and it works like an absolute charm. I am very pleased with myself with thanks to you! :-)

[@KF8OD1]

Great to see others promoting the L network tuner! I have used it with a ladder line dipole for years. They work great, broadbanded.

[@CharlesHuse]

Remembering a kit I had when I was a kid, a coil, a variable capacitor, and antenna, an earphone, and a couple of diodes. This tuner you are making is a couple of components short of a crystal set.

[@radioguy19510]

I like that you don't complement things with a lot of theory. Making radio equipment isn't that hard and your videos show how easy it is to build things with stuff that you have laying around. Now you've got me thinking about making one of these. KF0XO

[@lowellyates7404]

Once the coils are spaced evenly, a dab of hot glue would stabilize the wires even more. Enjoyed the video.

[@morris3881]

This video is three years old. But that's not what matters. Thanks! A very useful training video for all radio Amateurs!

[@wilbertbregar2297]

I enjoyed your L- match videos. I have been using a home brew L-Match tuner for about 3 or 4 years at 100 watts with BC capacitors. I call it my "Serial Box" made of wood with cereal box cardboard glued on to give it a finish.

[@lauriejones3198]

Well done. I watched the original build just before this one. What an excellent resource project. Many thanks.

[@cuban9splat]

This project is a big success! Nice clean wiring inside and the printing labels work great. Avery makes several different sizes of stick-on labels that are very handy to use for projects like this. After you stick them on just a little clear spray paint seals them right up. Very nice job, Kevin! 73 DE K7RMJ Frank

[@taki8592]

Kevin thanks about the tuner desciption I have been using it for years now. Very effective till 100watts. It is my primary tuner although I have z match mfj. 73 de Z33ST

[@acestudioscouk-Ace-G0ACE]

I liked seeing how the Mk1 evolved into the finished and highly useful Mk2 version. Will now watch the crazy matching video.

[@closeoutsaleusa5322]

I have built and continue to use an L Network like this at the feed point of a 17 meter Homebrew vertical antenna to keep the feed point at 50 ohms. It works great.

[@imahamjim]

One of my favorite videos kevin. Get well and hurry back. Jim

[@danl2825]

Great DIY project. Can't wait to see how it works in the field.

[@KuriosPC]

I just saw your first build, and I was going to suggest to build a portable version. And then I saw your description and saw that you made this video. Awesome.

[@loughkb]

I've used it in a few other videos since. It's working out to be a nice and useful little tuner.

[@BarefootBeekeeper]

The "suck it and see" approach has always been my favourite.

[@Fishermanfred1]

That was a wonderful idea on that coil Kevin. I would have never thought to do this. I'm going to try to find some or these plastic dividers. I hope they will be at a hardware store like Lowe's or home Depot in the electrical Dept. Thanks ,Fred.

[@jrfoleyjr]

I looked at Menards and Home Depot... no luck. Can anyone source those divider/grommets?

[@hectorpascal]

The math really doesn't matter if you've seen enough examples, and know roughly what to do! The coil construction in particular is very like some professional gear, but using common materials. Kudos Kevin! (I note you used thicker coil wire to compensate for the loss of Q with a smaller diameter former!)

[@alexxxx9709]

A smart reminder: Switch the in and output to tune a antenna witch is shorter then a quarter wave length if it does not tune fine.

[@Ratchet2]

Look for Panduit GE85-C grommet edging strip for the inductor wiring.

[@jkbish1]

That is the stuff. I checked it out on ebay and bought some. GE85-c is the stuff. I was going to use some rubber tube for the separation, but Kevin used the "right stuff." Thanks for the information.

[@jimawhitaker]

I like this video, I can watch you build this and get it out of my system before I have to struggle with it. Thanks for allowing me to live vicariously through you ;-) 73

[@deanhutsell3144]

Nice Job Kevin! I built an L-match similar to that with a home-made air wound enameled wire coil. I didn't use any math either and it seems to work okay for me. 73's Dean AC9JQ

[@vk6jn-vu3vwb32]

Fantastic ! No fear, no worries; just trial and error approach. And it works beautifully ! I wish I could try this, but don't have any more high quality metal gangs with me now.

[@DucatiMTS1200]

Great job Kevin - great to see practical genius at work.

[@prepared4anything]

Love this video. I am going to have a go at building one of these. Thanks for taking the time to make and post this video. On a side note when setting out your graphics for the decals it would be quicker and more accurate to just scan the front and back panels into inkscape using your scanner.

[@loughkb]

I used to use that method when duplicating extruded parts for 3D printing. My neighbor had these little plastic clips that held parts in place on his window blinds. He'd broken two. So I took a good one and laid it on a flatbed scanner to get a profile. Scaled it in inkscape and then traced it to get a simple vector representation of it. Took that file into Blender and extruded it, exported as an STL file which the slicer on the printer software had no problem with. I made him 10 spares in about a half an hour.

[@zsradioham]

Perfect. I need to build myself one fro my EFHW. Tnx for demonstrating the nice homebrew tuner.

[@rivit90]

does the capacitor need to be isolated/floated ? brilliant informative video cheers

[@loughkb]

One side of it goes to ground anyway, so that side can go to the metal chassis along with the ground side of the SO239s.

[@rivit90]

Thank you 😊

[@brucefredrick4200]

Nice and easy, but doesn’t the tuner coil radiate as an antenne? Any thoughts on what percent of radiation is lost or redirected? Is it enough to worry about. Seems that being able to tune to 1.0 would compensate for losses. Really nice setup, especially with the switches.

[@paulschmolke188]

Nice project. Came out looking good.

[@joserivera9636]

Buen trabajo 👍 Una consulta cuántos watts maximo soporta o se puede trabajar?

[@loughkb]

It's a low power tuner. It's in the title, QRP antenna tuner

[@thuff3207]

Thank you for posting this video. Yes I would like to see the calculations but I understand how and why this works.

[@JKarle]

Nice build, I learned a few things for similar a future projects. 73 Jason VE1AJK

[@pd1jdw630]

Ha down to the math. I love the “ lets build and see what happens “ approach.

[@bobsullivan5714]

BZZZZZZZZZZZZZT...............poof

[@mikepeirson1150]

Thanks for video Kevin just helps in my learning of SWL. I built the earlier model and it works great. Is there any advantage or disadvantage using magnet wire or thicker wire. Same question is there any advantage to using magnet wire close wound.

[@loughkb]

In a transmitting application, thicker wire and wider spacing are needed under higher power conditions. For receiving, anything can be used.

[@mikepeirson1150]

@@loughkb Thanks for reply Kevin, I am just a listener so that has answered my questions for me.

[@paulphoad]

Unfortunately, the metal enclusure forms a shorted turn secondary"turn" which absorbs power. If you can somehow "break" the loop by having insulators or gaffa tape between lid and body, would heip.

[@loughkb]

Just about every commercial antenna tuner that I have ever seen is in a metal enclosure.

[@paulphoad]

@@loughkb yes, you're correct. Also IF transformers etc have a can...I was overthinking. 😄

[@Alan2E0KVRKing]

Nice tidy job there!

[@eugenepohjola258]

Howdy. Nice of you to sacrifice your time to really walk through interesting issues. I don't agree with my colleague about one thing with antenna tuners. He claims that one may get a badly unresonant antenna tuned. Yes. But it will radiate just a small percentage of the input. My thinking is that any antenna tuned to resonance with a tuner will radiate almost all of the input. I admit that some power will be dissipated as heat in the coil. Also I admit that the radiation pattern will be irregular and that much could just shoot straight up. What might be your opinion ? Regards.

[@loughkb]

Antenna tuners are best applied to extending the usable range of a resonant antenna. The less of a mismatch, the less power lost.

[@fabiomeneghim4149]

Wonderful project. Congrats from Py2top.

[@kf4dcy501]

I like the binding post. but I would also back them up to use a twin lead feedline with an added balun or long wire use. like that in a dentron supertuner.

[@kf4dcy501]

I suspect it will happily handle 100 watts to posible a 300 watt transmitter.

[@kf4dcy501]

with a good antenna analizer / network analyzer, you could pick a center band frequincy and tap the inductor for that frequincy with caps centered half way.

[@kf4dcy501]

I might would add shielding, using aluminum duct tape on the plastic side panels.

[@loughkb]

I doubt it. The plate spacing on that cap is really tight. RMS RF voltage on an HF 100 watt signal is going to be up around 600 to 800 Volts. It would arc for sure.

[@kf4dcy501]

I will admit it's a sweet box. I never contemplated ink jet printing labels. but I like screen printed adhisive films better.

[@michaelaschuler7326]

Great job :) , i have one question, how ist the name from the comb rail from the coil? I can't find this to buy.

[@loughkb]

Search down through the comments in this video or the previous one. Several people found them and posted links.

[@SpinStar1956]

Did you ever make the field test video of this tuner; do you still use it currently? Would you change anything? I was considering building this and wondered if you still liked it in this video's form. Tnx & 73...

[@larspregge6420]

Does it need to be a air coile, or can it be an torroidcoil? Last one should be smaller, or not?

[@morsecode4666]

Nice video well demondtrated . I my self use the the capacitors as the tapping point

[@JCCB11360]

This tuner works for 10, 11 and 12 mts. Thanks.

[@martymctry20]

Hi Kevin! I have an end fed wire antenna 26.5 m with unun/choke and about 20 m coax cable 50 ohms. The 9:1 unun should adapt the impedance so despite this would the l-network help further if it's placed between transceiver and (long) coax cable? I'm just restarting my hobby after 37 years and working on my technical skills to get the hang of it after this long period of time... Thanks for your great work - already helped me a lot! 55, 73, DF7ED

[@loughkb]

Yes, it should work fine for tuning the end fed. If you build it, just make sure your wire runs are as short and neat as possible to reduce stray capacitance. Also, if the variable cap has close plate spacing, be careful on power.

[@martymctry20]

Thanks! Finding a properly spaced cap is quite difficult so I decided to test an old radio adjustable. With my 20 W rig it should work as you said in the video otherwise I have to search for a bigger and more expensive one... Keep up the awesome work ! DF7ED

[@jkbish1]

I could not find a resonably priced case for the project. Then I noticed I had stored (for some reason) an empty Kirkland European Cookie Tin in the garage . It is 11inch x 8 inch x 4 inch. A ham could buy a new box at Costco and do whatever with the cookies. Still cheaper than buying a new box.

[@theodoresears4679]

Great video. Thank you for being good ham.

[@jkbish1]

it would really help if I knew the "name" for the "grommet material". I will keep looking but sure would like to know how to name it.

[@loughkb]

Scan down through the comments. I think there were three or four that commented with links to where to buy it.

[@jkbish1]

I scanned down as per your comment. I ordered the GE85-C strip and an air variable capacitor from Ebay. I bought the pvc (and some screws) today at the store. I sure am glad I saw video. I will work on my pvc tube until the stuff comes from Ebay. Thank you Kevin !

[@jrfoleyjr]

It is the Panduit GE85-C strip. It is carried by Mouser [part no. 644-GE85-C] and Digikey [part no. 298-13452-ND] in small quantities. At Newark Supply and on Amazon you might have to hike up your shorts to buy because they want too much for this project.

[@elrazky]

Nice video thank you for sharing it, I would like to get the name of those spacer sticks... where do you think I could buy them from or at least what are they called?

[@loughkb]

Read down through the comments. There was a couple that found sources for that material.

[@elrazky]

@@loughkb got it. Thank you.

[@ElektroLUDIKITS]

Nice video and nice use of Open Source software !

[@loughkb]

Thanks. I'm all open source here, all my machines run linux.

[@MoTown44240]

Nice tuner video. Want to find out what that plastic strip is called I would like to order some. 73, Terry - KB8AMZ

[@loughkb]

The strips were given to me by another ham. He didn't know where he got them. I *think* they're some kind of industrial grommet material that you could line a hole in a metal panel with.

[@MoTown44240]

Yes Kevin, I know that from your comment to Richard Day. I read all the comments on your channel before making my own comment. I wasn't really expecting what the bit is called or where I might find it. I would like to know, for future projects, what it is called and where I might find it. I guess that I was thinking via print. Like thinking aloud. Not directing the comment to any specific person. I am not sure how I will go about searching for this product but I will try. If I find the answer I will let you know through a comment on this video page. 73, Terry

[@MrTimowens]

www.mouser.com/Search/m_Search.aspx?Keyword=grommet+strip

[@RobertTKlaus]

www.amazon.com/Yongcun-Slotted-Grommet-Movable-Bushing/dp/B01JKEJD86

[@jkbish1]

"Panduit GE85-C grommet edging strip", it is available on Ebay. I just ordered some. This is a key part of the project. You get 5 pieces for $7.91 including tax. They should pay Kevin a fee !

[@jerryuhte1568]

Kevin, good job, nice work too ! Keep it up om, 73, Jerry K9UT

[@SjaakBuunk]

Does it also work with a magnetic loop antenna for qrp use?

[@loughkb]

You would not want to use a separate antenna tuner with a magnetic loop. You want to tune the magnetic loop to the operating frequency. If you try to use a magnetic loop even just a few kilohertz outside of its resonant frequency, it will be extremely inefficient. It's a very high Q antenna.

[@janetwinslow2039]

Is the antenna at the L/C junction or the other end? I couldn't quite see.

[@loughkb]

In this case, at the L/C junction. One function of an L network tuner, is that it matches a low impedance at the inductor-only end to a higher impedance at the L/C end. If your antenna is presenting an impedance lower than 50 ohms, you can switch it around the other way to obtain a match.

[@denizyildiz8904]

Hi Kevin..it is me Deniz from Turkey again..I ve just finished my anttenna tuner..and your project and videos helped me too much..first, thanks for this again..I wanna ask something else about tuner..is the variable only necessary for transmitting for swr? I will only use it for listening sw..do I have to use a variable or it is not important for listening only? I see you use the variable for swr anf of course for transmitting..thanks so much

[@loughkb]

Yes, it's still important. The tuner is matching the complex impedance of the antenna to the expected 50 ohms at the radio. Even when receiving only, this matching will allow for more efficient transfer of RF from the antenna to the radio and improve things. Just tune by ear, listening for the noise floor and signals to peak.

[@denizyildiz8904]

@@loughkb thanks Kevin..one more question please😊 The variable I found in an old radio 50-360 pf..And I used this in my tuner..is it enough or do I need a larger one, for ex 500 pf?

[@loughkb]

@@denizyildiz8904 I'd think that should be enough. It really depends on the antenna. If it's too far out in impedance, you'll need more capacitance and inductance to match it.

[@ryanjones9305]

Really cool project!

[@branhamj368]

That was very interesting. How much power could that tuner handle? Thank you for sharing.

[@loughkb]

With the close spacing on the capacitor plates, 10 to 20 watts max. Maybe more, but you'd risk arcing across the plates.

[@theodoresears4679]

Do the L network tuner match the antenna to the receiver on the transceiver.

[@denizyildiz8904]

Hi..I saw a different project ..one side of the coil was empty..not to direct antenna..but in your project one side is connected to radio and the other is to antenna..whic one is best ?

[@loughkb]

I've only ever seen the L network design that I used. It's standard and has been used for decades.

[@denizyildiz8904]

swling.com/blog/tag/swl-antenna-tuner/

[@denizyildiz8904]

@@loughkb in this page one side of the tapped coil is empty(no connect anywhere)..but in your project this side is connected to the radio..but in the page only the main pin of comutator is connected to the radio but not the end of the coil.

[@denizyildiz8904]

@@loughkb www.hard-core-dx.com/nordicdx/antenna/lab/tuner.html

[@denizyildiz8904]

@@loughkb so which is true?

[@AliciaGonzalez-cn3ln]

Why you got more SWR in 40m compared with the big coil you used in the old project?

[@loughkb]

Differant antenna.

[@jrfoleyjr]

What was the number of the mfj swr bridge you use?

[@guillermosempron5776]

You forgot to put an interruptor to switch the capacitor from the inputo to the output to transmatch a low or high impendance antenna.

[@denizyildiz8904]

Please can u share a sheme or a photo for the connections? Thanks

[@loughkb]

It's shown in the previous video. I think I linked it in the description.

[@denizyildiz8904]

Thanks..I Have just seen

[@richardt6813]

What size wire did you use on the coil???

[@loughkb]

My application is mostly QRP, so I just used some doorbell wire I had sitting around, maybe 16 gauge, I don't quite remember.

[@richardt6813]

@@loughkb Thankx! Working on mine right now.

[@kf4dcy501]

could you or would you make a vid on a vhf and or a uhf transmatch.

[@shanescustomwelding]

So how many turns on the coil on 1in PVC I think mine has 18 turns but something's not right it won't tune I think the problem may be the small capacitor I have but. I was just wondering on the turns. Thanks

[@loughkb]

It depends on how far off the load impedance is. Also frequency. So a shorter antenna and a lower frequency might need more inductance. Use an antenna that's closer to a resonant length or add more turns.

[@shanescustomwelding]

@@loughkb ok thank you ill keep that in mind

[@shanescustomwelding]

@@loughkb could resistors soldered in series with taps added be used in place of the inductance coil and if so which has better performance? also if resistors can be used which ones should be used. i know im asking alot thank you for passing on the knowledge i appreciate it

[@loughkb]

I can't think of any reason why you'd want to put resistors in there. It would just eat power, kill efficiency, and probably burn them up.

[@shanescustomwelding]

@@loughkb ok thanks

[@gerryorlandostagehand3705]

That was a awesome project! Nicely done. Can't wait to build it. Gerry KN4KOT

[@jeromegrzelak8236]

Lable the position of the inductor for better referance also the cap good build i bet u can get 100 bucks all day 73 kg6mn

[@fredriko.zachrisson9711]

Can you tune without a SWR meter? What would the results be?

[@tiempoder]

Yes. The FT-817 FT-818 and others transceivers have internal swr meters. You can read the swr adjustment directly on the screen.

[@WingoCabrera]

Wonderful work!!!!!!!

[@HK6E]

Hi Kevin, what would be the maximum power that can handle this tuner?

[@loughkb]

Hello Pablo. The limiting part is the capacitor. It came out of an old AM broadcast receiver. The plates are very close. I wouldn't want to try more than 20 watts with this capacitor, and that might arc over, I'm not sure. The wire, coil, and switch could handle 100 watts easy, so with a cap that has better plate spacing, you could go higher.

[@DavidGillooly]

I have seen other builds with this type of cap and they seem to be OK at 5 Watts CW.

[@steveoshaughnessy3736]

It looks like they're called Caterpillar Grommets.

[@jrfoleyjr]

Steve, Found it! It is the Panduit GE85-C Strip. It is carried by Mouser [part no. 644-GE85-C] and Digikey [part no. 298-13452-ND] in small quantities. At Newark Supply and on Amazon you might have to hike up your shorts to buy because they want too much [$50-100 for quantity] for this project. 73 de w8nsi Jim

[@lawrenceazzopardi7386]

I thought that L network is field friendly ! :)

[@tribhuwanaa.s2684]

Nice Tutorial Video...is this for all band (HF, Vhf, and Uhf)?.....T.Bhuwana YD0AAB ,...73

[@loughkb]

HF.

[@tribhuwanaa.s2684]

@@loughkb Thx U..., do you have Vhf ATU schematic..?

[@loughkb]

@@tribhuwanaa.s2684 Nope. I can't remember ever seeing one. Why would you need one? Antennas are pretty broad banded up there. Something like a disccone provides a decent impedance match over hundreds of megahertz.

[@tribhuwanaa.s2684]

@@loughkb Thats good....thx u 4 your adv...(Yes..use discon antena...👍)

[@tribhuwanaa.s2684]

@@loughkb 73

[@OkieRCguy]

how did you wire in your bypass switch?

[@loughkb]

Just a switch that shorts the center of the input connector to the center of the out put connector. Each center can go to the middle pins of a DPDT switch. Short one sides pins, send the other sides to the in and out of the tuner circuit.

[@OkieRCguy]

@@loughkb Thanks. I got everything else, but for some reason, the switch just confused me. I guess I'm getting senile!

[@sputnik4216]

Does it generate or augment harmonics?

[@loughkb]

If anything, it would reduce them by providing a better match at the operating frequency.

[@danielerdman7543]

Very good job ! Dan N7CVG

[@richardnday]

Your furnace should not cycle on for such a short time. You are wasting a great deal of money. I did watch both videos, and liked them very much. I'd like to know where to get the plastic you used for the inductor.

[@loughkb]

That was just a piece of 1 inch PVC. The finger strips I think were gromet material for lining holes in metal chassis. Those were given to me by another ham, I don't know where he got them. You probably heard the fan doing a short run post-cycle. The fan is temperature controlled by a thermal switch in the heat exchanger. Most times, after a furnace cycle, there's just a little heat build up that trips the switch for another 30 second fan run to push that remaining heat into the house.

[@ccwynn6657]

Need to show DPDT isolation (bypass tuner) part of circuit. Ganging contacts on the switch to help with liability will defeat capability of isolation.

[@humaxf1]

Nice project. 👍

[@jcmcclain57]

I really like your channel. I just got back into the hobby and your project posts are great encouragement. KC9OWR

[@buffplums]

Nice work

[@daviddavidson1372]

the best name i found for the plastic part is grommet strip.below is a pic and video.aleast we have a name.also seen it called grommet trim.also search youtube for more videos about grommet strips.. www.hiq.co.nz/products/category/GROMST-grommet-strip

[@MoTown44240]

David, thats it exactly. Thanks for offering this information. Now order some for the junk box. Anything to tidy the winding of wire by hand with equal spacing is a great aid.

[@JamesP6084]

Great Job Kevin. 73's VK6NJP

[@Travis141123]

Now I know what to do with all those heavy cardboard cores I've been hoarding away...

[@jeromewysocki8809]

scott king , and I thought I was the only one who hoarded these things for eventual use as inductors 😁.

[@robertwolf4043]

Awesome!

[@ab1dq593]

Nice work, thanks for sharing & 73 de AB1DQ.

[@jrfoleyjr]

For standoffs, I am using some plastic computer mother board standoffs.

[@АндрейК-п9д]

It's a good homemade!

[@KA4UPW]

Hahaha TenTec made one almost exactly the same.. even in the same box.. id send you a photo.. if youd like.. BTW your's is nicer

[@DeeegerD]

Very nice but you should have done the math ;)

[@peterpauldonoghue7024]

kzbin.info/www/bejne/e4mnaqV3hLKSpZY

[@mr1enrollment]

The every man approach is why engineers have no respect for Ham radio.

[@TheMrKrause]

First

[@kd8opi]

Just missed it!.

[@josephstellini6911]

a very good job

[@pablomiranda1884]

Great video! CE3RLW!

[@on4mgy_radioamateur]

Great video, nice build ! 73 de ON4MGY Nic