#387

This video shows how to build traps for a 40/30/20m EFHW antenna using a nice kit from N7KOM. We start with the intro into why I am doing this, how to wind the toroids, then how to setup and test the resonant frequency of the trap. Methods for adjusting the toroidal inductor are shown in order to move the resonant frequency to the desired point. An antenna analyzer like a RigExpert is used to test for resonance. I also how how a Dip Meter and Frequency Counter can be used to check the resonant frequency as well. Links for the inspiration (VE6LK video) as well as the trap kit (N7KOM) and my toroid winding tutorial video are all show below the table of contents:
00:00 - Introduction, and reason for doing this
01:17 - The N7KOM trap kit
02:00 - Winding the toroids
03:14 - Soldering the capacitor to the PCB
03:50 - Heat strip toroid wire for testing
04:35 - Tack toroid to capacitor for tuning
04:47 - Setup and theory of tuning the trap
06:24 - Tuning process - trial and error
08:02 - Ready for assembly to PCB
08:26 - Completed PCB for re-tune / check
08:57 - Heat Shrink and re-touch-up tuning
09:33 - Dip Meter for testing resonance
10:33 - Wrap-up
Links:
Vince VE6LK video:
• Discover the secret in...
N7KIM trap kit:
www.etsy.com/listing/15952575...
W2AEW "how to wind a toroid" video:
• #151: How to wind a to...
Part II: Building and tuning the antenna!
• #388: Build, tune and ...

[@JonathanKayne]

Im glad you are planning on making this a multi part series, because I've wanted to play with traps but never did because how i actually add it to my EFHW isn't intuitive. Seeing how you do this will be incredibly helpful!

[@w2aew]

Thank - I hope to find time to build the antenna this weekend.

[@craxd1]

People don't recognize the grid dip meter anymore, it seems, as a great tool. When building tuning networks, I still use one.

[@VE6LK]

Alan, thank you for the [as always] most excellent and patient explanations in your build videos like this one. You captured the build process of these traps really well but without the colourful language that I employed off-camera :) And now I know a bit more about a grid-dip meter too. vy 73 my friend de VE6LK

[@w2aew]

Thanks for the inspiration. I wonder if you could share your final segment lengths from your antenna with me?

[@VE6LK]

@@w2aew oh whoops I forgot that .. standby .. .getting tape measure .. Individual wire lengths: 80 1/4" end ele .. 45" mid ele .. 354 1/2" to feedpoint.

[@dkabell]

Thanks for showing the grid dip freq meter technique. Always learn something from your videos.

[@sasines]

The most interesting piece of equipment in this video was the Heathkit grid dip meter! Ahhh the good old days !!😊

[@allenlutins]

What? Not the nixie tube frequency counter!? This is a fantastic video. I was recently gifted (!) an Elecraft KX3 and plan to start doing some portable activities (want to operate from Balsam Lake Mountain in the Catskills - one of the "15 high peaks" but sadly not formally eligible for SOTA due to some geographic anomaly). I have a portable vertical, but this looks like it may be superior (especially regarding weight).

[@Swamp-Fox]

Nice to see the grid dip meter in use on your bench! 73, Patrick KF4LMZ

[@PapasDino]

Always great to "re-learn" the tricks of the trade of working with toroids! 73 - Dino KLØS

[@tcarney57]

That's a pretty-clever design with the strip of PCB with capacitor running through the toroid.

[@syshero]

This is a really well-timed video. I just bought some wire to build an antenna. Just got my QMX for 80/40/30/20 and I was looking on how to build an 40/30/20 antenna

[@jawaidmughalmhsh7012]

Hello Sir, after a long time you have posted a video. Jawaid. (Pakistan Amateur Radio Society Club operator. AP2ARS)

[@survivalcomms]

Very cool ! I still have an HD1250 in my collection. I'm jealous of your freq counter. Thanks for sharing !

[@dougn7bfs]

If you have a lady in the house she probably has some clear nail polish that can be used as a coil winding fixative in a pinch ;) Thanks again for all your great videos Alan 73 Doug N7BFS

[@MichaelLloyd]

That's a nice looking little trap. I also enjoyed the grid dip meter use part of the video. Your toroid winding method makes it so easy. 73 NE5U

[@wadepatton2433]

The very first time I looked at POTA activations I saw your call. Haven't work you yet, but well may, didn't hear you. I've built a few of the "full scale" EFHW's and have been running one for a few years now as my main HF antenna. Great to learn more about building them, and a smaller scale to boot. Thanks es 73, W1ADE

[@w2aew]

EFHW are very under-rated, I think they're fantastic. I'll keep an ear out for your call!

[@N7KOM]

Well done, Alan! What a fantastic and clear build video. Very cool to see the results in the dip meter and frequency counter too! I'm looking forward to seeing the final antenna! 73 de Tim N7KOM

[@w2aew]

Thank YOU for the nice kit and thorough instructions!

[@MattHeere]

My POTA EFHW is a linked design. Doesn't help the 65 feet of wire problem, but it does get me on every band between 40 and 10 with no tuner. I've used that same wire without the UNUN as a 1/4 wave on 80M, although that typically does require at least a 3:1 internal tuner (and radials of course). I may build one of these though. I built a dedicated 20M QRP version to go with a QCX mini. Now that they have the multiband version of that radio a more compact multiband end fed would be handy.

[@DM-fz3ly]

Thaks Alan for the great example. I was expecting you to try to interpolate the dial on the Heathkit and was surprised to see you read it with the freq counter. In the next video can you include some schematic drawings and explanation as to why you chose the tuning freq for the traps and what effect they will have, etc. Thanks for sharing your knowledge.

[@w2aew]

The dial on the dip meter isn't nearly accurate enough to target the desired frequency. I'm taking the target frequencies from the N7KOM instructions. Schematic is included in them (simple parallel LC circuit).

[@ornithopterindia]

👍Thank you sir.

[@MIKROWAVE1]

Excellent video Alan! You can get a bit more dip by using the original longer leads and coupling between the wires that go to the loose cap. Traps are fun and practical and chunk of 1 inch PVC tubing and some #14 enameled and a few inches of coax as a capacitor will do the same as the torroid and chip cap and allow up to a few hundred Watts. Tuning just below the band is great advice!

[@w2aew]

Can you elaborate why tuning just below the band is the right thing to do? I haven't really heard a definitive answer to this yet...

[@MIKROWAVE1]

@w2aew That question is itself a trap. My personal opinion is that we do not need to do any more than to take W8JI's measured data as guidance.

[@w2aew]

@@MIKROWAVE1 I'll go check that out.

[@pauldenisowski]

Great video and always nice to see the dip meter in action :) 73, KO4LZ

[@wb7ond]

I suspect the trap tuning methodology is the same for the ubiquitous NanoVNA... Seems, I am going to buy another EFHW contraption soon. (:-).... I "splurged" for the previous qrp EFHW you showed, and it works great. Thanks the all the great videos.. 73s.

[@w2aew]

Yes, tuning will be the same with the NanoVNA

[@timg5tm941]

Excellent video.

[@dean5263]

Thanks for the video.

[@karlbesser1696]

A good idea to do it with the BNC banana plug adapter. ✔️

[@w2aew]

Works well enough at HF

[@norbertdapunt1444]

Awesome.

[@tav9755]

Again that was very useful. Never thought of using the antenna analyser that way. I would be curious how you tune the entire antenna.

[@w2aew]

Hopefully I'll be able to make a video when I build/tune the antenna.

[@t1d100]

I am not a HAM, but I watched the video, because you are a great teacher and I knew I would learn something. And, I did ! Thank you. Ideas = Rusty Oleum brand makes a clear spray paint that is safe for plastics. Maybe lightly spray the coil, after you have it adjusted, to tack it in place, so that it will stay put, when you cover it with the heat shrink? I would think that you know all the tricks of shooting a string into a tree, with which to haul up the antenna... Bow and arrow, sling shoot, or even a fishing rod... A bow and arrow may not be permitted in some parks, I would imagine. Cheers!

[@t1d100]

Ooo... DIY an air cannon with PVC to shoot a tennis ball with the string attached... Just don't make it look to much like a WMD...

[@andye2005]

There is a product more generally available in the US called Q-dope. It's basically polystyrene dissolved in a solvent such as Toluene. It has practically zero effect on the tuning. Rather expensive in the UK, so I just found some Toluene online and dissolved some polystyrene in it about 5g poly to 30mL solvent. Got enough solvent to last a lifetime! Andy

[@w2aew]

I use an arborist throw-weight and some light-weight throw line to get a line into a tree.

[@MikeWest_W]

Now I have to learn about grid dip meters.

[@RobB_VK6ES]

It might be enlightening but from a practical point of view a waste of time. I doubt these are even made any more, using the Nano VNA is superior in every way. Think crystal set vs SDR.

[@w2aew]

I did a video on them.....

[@aduedc]

Thanks for showing how to build one. However, I would like to learn the science behind it, so I can design one.

[@w2aew]

A trap is a parallel resonant LC circuit. Check out this video on resonant circuits: kzbin.info/www/bejne/nqLLh2hmbZploKM

[@aduedc]

@@w2aew Thanks I already know about resonant tank circuits. There are other effects such as concentration of fields inside ferrites (which is 1000 times more than free air) and make good receiver antenna, but not good for transmitting because of ferrites hysteresis that leads to power loss. Also, matching the impedance of the antenna to the input of the receiver, because a short dipole (compare to wavelength) have very high impedance and we need to use things like inductor to better match the antenna.

[@W1RMD]

Really cool Alan! Being that I've been a ham for 30+ years and outside of common mode chokes, I've never used toroids. THIS is a great project to practice on! It so happens I went through my junk box and I have about 15 of these T-50-2 toroids this is good news! They look A LOT bigger on camera. I wonder how well a NanoVNA will work to check this circuit? Thanks and 73! - W1RMD

[@w2aew]

A NanoVNA can be used in much the same way as the RigExpert

[@W1RMD]

@@w2aew Thanks!

[@Homer19521]

Glad your RigExpert is still working. My AA230Zoom took a dump. Gigaparts & RE USA could not help fixing it. My appeals to RE Ukraine went unheeded. Disappointing experience. Great vid. 👍

[@w2aew]

Sorry to hear of your troubles with the RigExpert.

[@KK1W]

The only problem I've had with my AA-55z was overzealously pushing a poorly soldered PL259 into the socket (it had a solder blob on it). This caused the center conductor to break away from where it was soldered on the AA-55 circuit board. Worth checking and an easy fix if that's your problem.

[@BobGarrett66]

Excellent video Allen. Thanks for posting it. Can you share some info about your particular EFHW? Was it a kit build or did you put it together yourself? Thanks and I’m looking forward to the follow-up! 73.

[@w2aew]

Check out the video posted today (#388). It shows the antenna build/tune/test. The traps were a kit from N7KOM, the UNUN was from SparkPlugGear, and the wire was a hamfest special...

[@BobGarrett66]

@@w2aewHey Allen. I just watched that video. Excellent job!! The EFHW I was curious about is the one you show at the very opening of this video. I didn’t know if you bought it as a kit or brewed it up yourself. Thanks!!

[@w2aew]

@@BobGarrett66 I picked it up at a hamfest here in NJ a few years ago - made by a few local hams. I made two changes to it - I added a right-angle BNC connector to it, and replaced the wire (after I broke the original).

[@BobGarrett66]

@@w2aew Gotcha. Thanks for the reply.

[@TheH3nrydesign]

👍

[@Dave-AA0IW]

Great video! I am curious, a normal (~67') 40m EFHW will get you on 10, 15, 20 & 40 meters. If the wire is now significantly shorter, and you have a "dedicated" 20m "section", do you lose 10 & 15 meters?

[@w2aew]

Yes, I'll lose natural resonance on 10 and 15m. For me that's an ok tradeoff since I don't use those bands nearly as often.

[@adrian_sp6def]

Few questions: Can I use nanovna? What is efeciency of trapped EF relative to full EF? How tuning frequency was chosen?

[@w2aew]

Yes, a NanoVNA can be used in much the same way. Efficiency on the 20m band will be the same as full EFHW (because there are no traps). Efficiency on 30 and 40m will be a little lower (as is always the case when you have some inductive loading coils). Frequency was chosen to be just below the band so that at lower frequencies, the trap will appear inductive.

[@gretalaube91]

I thought traps were resonated for the frequency you wanted to operate, like the CW portion, not below it. The zepp's got a high Z, so the trap's gotta be high Z, too. Sure, the dang thing's gonna go off as soon as you put them wires on it and breathe on it, so maybe that's why you're aiming a little low, right? 73's DE W3IHM.

[@w2aew]

I was going by the advice in the N7KOM instructions - assuming that things shift once you add the wires to 'em.

[@FXGreggan.]

Wish you'd explain why you want it resonant at 13.9MHz, below the band of choice...

[@w2aew]

I operate primarily CW, so I'd like the trap to provide good action at the low end of the band. Below the resonant frequency, the trap appears primarily inductive, effectively shortening the required wire length of the next wire segment for the next lower band.

[@FXGreggan.]

@@w2aew Cheers, I love how you explain stuff - even my sometimes slow brain understand your explanations.. you should have been a teecher :)

[@doctave]

@@w2aew but then why not 14.0 ?

[@w2aew]

@@doctave To be honest, I'm following the recommendation in the N7KOM build instructions. I need to do a bit more study on why the resonant point is set 100kHz below the band edge, which makes the trap appear capacitive in the band of interest (maybe having something to do with the effect of the wire on the far side of the trap)

[@thedmutz]

@@w2aew In the past I made a trap for a 6M/10M dipole and centered the trap in-band and found that it didn't work that well for me. So seeing your video and realizing that the trap should be set slightly lower in frequency gives me some clarity and a bit of relief! I don't fully understand why still, but somewhat glad to know I just probably did it wrong :)

[@kk6onl]

literally learning cw so I can catch you via pota....

[@w2aew]

Great! Good luck on your journey with CW. I have found it is a continuous process, slowly getting better over time.

[@zsradioham]

Was this experiment for QRP?

[@w2aew]

Yes.

[@jstwinkles]

Who's a good supplier for toroids?

[@w2aew]

One decent supplier to the amateur community is kitsandparts.com: kitsandparts.com/ www.kitsandparts.com/toroids.php kitsandparts.com/WA2EBY_toroidkit.php

[@tamaseduard5145]

73' 88 '

[@John.Doe.2025]

69' 0100'