HF Antenna Micro-Traps - DIY Build Project
Вставка
- Опубліковано 28 сер 2020
- This is the one you've been waiting for - the traps to go with the micro End Fed Halfwave (EFHW) antenna build. Here's how to make them.
These traps will work with my Ultimate Ultralight EFHW ( • Ultimate UL Portable R... ) or just about any QRP end-fed halfwave antenna, and you could even build pairs to use with a dipole.
LINKS:
- LC Resonance Calculator: www.omnicalculator.com/physic...
- Toroid Winding Calculator: www.66pacific.com/calculators/...
You'll certainly need some MATERIALS:
- T37-2 Toroids (my usual): amzn.to/3hFsYlj
- T50-2 Toroids (a little more efficient and maybe easier to build): amzn.to/2QCkGio
- 28 ga Magnet Wire: amzn.to/3b9Isf4
- 39pF 100v Ceramic Capacitor (0603 case recommended): www.digikey.com/product-detai...
NOTE: 100v is marginal for 5w. Consider a 500v or 1kv for better durability and/or higher power.
- 500v: www.digikey.com/product-detai...
- 62pF 100v Ceramic Capacitor (0603 case recommended): www.digikey.com/product-detai...
NOTE: Again, 500v model is needed for 10 or 15w. www.digikey.com/product-detai...
Also, consider a few other capacitors in the 22pF - 100pF range, depending on the traps you'd like to build.
- Perforated Prototype Board: amzn.to/35lcvzn
- 5/8" Heat Shrink Tubing: amzn.to/3lwwGjt
- 1/4" Heat Shrink Tubing: amzn.to/2G9bGzk
And you'll need some TOOLS:
- Dremel (or similar)high-speed rotary tool: amzn.to/3gFEkEL
NOTE: I have had my Dremel tool for about 25 years now and it hasn't missed a beat. Based on my personal experience, I would recommend going with the name brand tool.
- Diamond Cutting Wheels: amzn.to/2QBRHve
NOTE: I really like these because you can't cut yourself with them, but they cut the perf board and BNC connector brass just fine.
- Soldering Iron (any will do) with a fine tip: amzn.to/2GaENlN
NOTE: I've been using this one for about a year with no issues. The heat gun is AWESOME for hot air/solder paste construction. The iron works well for traditional soldering.
- Electronics Tweezer Set: amzn.to/2ENy00w
Please share your builds with me when you're done, and tell us about how it works out for you in the comments below.
Thanks!
de K6ARK - Фільми й анімація
I gotta admit that when I saw you doing the SWR on an unconnected toroid / capacitor , I said to myself , "What Magick is This?" , then went to the bench to replicate it! Excellent learning moment - thank you.
I know, right?!? This is pure art.
I finally built a trapped EFHW for 17/20/30/40, my favorite SOTA bands. Thanks for the great video!
Now that you have shown how to calculate how many wraps and the process....I have to build me some traps....another thing on my list to do...great. I blame you for all the things I don't get done. :)
I just sent this to a friend. "Either I'm smarter or this guy is good at explaining". Twenty minutes ago I had no idea how traps were designed or how you'd test them. Tightening/loosening the coils is a great trick. That must increase/decrease capacitance just a hair?
I'm definitely going to add traps to my repertoire. Thanks for the great instruction!
That was one of the best ham radio UA-cam videos I've seen in a long time. Very creative way to make a trap. I've made traps for many year but never gave any thought to making them the way you just showed. and......you taught everybody how to and how easy it is to make the traps.
Thanks for sharing, Barry G. Kery, KU3X/QRP
I learned more in 27 minutes than in 20 years of being an amateur, about traps, watching your video. It all makes sense now. I'm going to run out and build myself an end fed antenna. I need a nice antenna analyzer first.
Agreed, I learned the material to pass the test but now it makes sense!
Oh god it finally makes sense... and testing trap resonance with the analyser is brilliant. I thought you were going to DIP meter it - but it achieves the same thing!
Adam.... don't ever stop with the build sessions. Awesome!
Excellent, I love watching your mini, micro, pico projects!
You could teach a lot of people on UA-cam how to make a instructional video, very clear and concise I’m totally new to this subject and have learned more from this and the previous video than I have plowing through several hours/days of other people’s videos, thank you.
I have been so waiting for this video!
Incredible amount of information without flooding. Thank you.
Good timing. This is exactly what I have been doing the past few days.
I always learn so much from your videos. Thank you!
You make it look so simple. Looking forward to trying to build one! Thanks
Both the theory and practice are beautifully explained here. Now I feel confident that I will get a good result and will try some. Thanks very much Adam.
Hi Adam,
Excellent video. Found it interesting how you used the RigExpert to check resonance. Stay safe. 73 WJ3U
Well, one more project for the list. Thanks Adam. Good explanation of how traps work. I'm gonna need some more magnification to add to my bifocals. Great video.
I love your work. Its the perfect combination of science and art.
Thank you. A neat way to tune the traps.
Congratulations on the video. Very well explained topic.
Awesome build video Adam , I just may have to try this!
Thank you for this. I'm studying for my general class test, and this helps to drive into my memory what a trap is. Cheers.
this is just clear as it can be. He makes it seem simple!
Thanks for an educational video. I have a 3D printer and seeing these little traps, it gives me ideas for making my own.
I might try to build a 100 watt version but still keep portability in mind.
Really helpful videos on half wave antenna matching and traps - thank you so much for making them!
Mortimer Rhind-Tutt | UK /G4BSK / QRP Enthusiast
Well done Adam 👍
Thank you for all the information absolutely brilliant.
Very clever , well done! Awesome videos!
Been waiting for awhile to finish the efhw. I can see a Digikey order in my future as well.
I have to admit I´m becoming a fan of your cool small projects. :) Greetings from Chile. 73s
Well put together fella.
You should look into buying a Panavise. It makes holding those fiddly little parts stable while soldering and won't damage the parts.
Another brilliant design. Thanks! KD2SML. 7-3
Hi Adam - many thanks for the video - very interesting to see how you tune the traps, and also impressive to see how small you get them. One question about the toroid you selected - why did you go for material type 2? From my limited understanding, this material type has a frequency range from 240kHz to 10MHz, so it would seem they are not ideal for 20m traps (but ok for 40m). Is my understanding correct, or have I missed something? I would really appreciate a book reference where I can learn more about the principles behind antenna design (including designing transformers and traps). There seem to be many “recipe” books showing different antennas can be built , along with accompanying parts lists, but without detailed explanation about the designs - this isn’t what I am looking for! Could you recommend anything? Many thanks again!
Edit: I have found more information, so I will answer my own question in case others come. It seems that the type 2 material has a frequency range to 30MHz, not 10MHz as I wrote above. Both type 2 and type 6 material would be suitable, but the type 2 material has a higher permeability than type 6, so you can achieve the same inductance value with less turns. Clearly when making these microscopic traps, that is an advantage! Hopefully this helps someone!
Top Job Fella. very good visuals and explanation. Barnie M7PBX.
Great video!!
Your videos are the best. Building these is probably a bridge too far for my eyes at this point but who knows...
Nicely Done! Especially enjoyed the trap testing with the antenna analyzer. Made it 3/4 through the video thinking he will need need pairs of traps per band (thinking center fed trapped dipole not end fed. Oops!). Headed to the garage to fine the epoxy and the magnet wire. keep them coming. de KB7ZUT
How’d I miss this? Treasure!
Thanks for this video, very well done. The trap are zn excellent idea. They do get stuck on tred branches, but using a telescopic pole, these are awesome.
Thanks again. 👍👍👍
73
Julian oh8stn
Wow, excellent video!
Some questions come to mind.
1.
When selecting capacitor and inductor components, how can we make a calculation to determine the maximum power?
What factors determine the power handling capability?
Is there a voltage or current rating for the capacitor?
Is there a voltage or current or inductive value or coil type or coil size that determines the power handling capability? What is the limiting properties of the coil? Does it come down to heat? How can we calculate?
Additionally, selecting different wire sizes like 28 AWG seems like it might have some effect on the maximum power handling capability.
2.
As we add more traps, inductive loading seems to shorten the overall antenna.
What calculations and factors can go into maximizing the bandwidth?
If we use really small inductor values and larger capacitor values, will we have more bandwidth in the final product?
How can we mathematically determine based on the capacitance and inductance values that we choose how long the final antenna will be? How long each segment will be? How much bandwidth will be lost as we add each trap?
I am interested in making a higher-powered version of this multi-band trap EFHW antenna and I'm struggling with trying to determine what the overall antenna length will be, what each segment will be after adding a trap and how to maximize the antenna to keep as much bandwidth as possible as well as keep resonance and reduce losses. It seems like there must be some relationship that we can mathematically determine and use to satisfy requirements or failing that, maybe your experience shows some rules of thumb that can help guide in the right direction?
For example, using smaller inductance values and larger capacitance values
Versus
Using larger inductance values and smaller capacitance values.
What do these choices affect on the overall design?
3.
Sometimes in videos like yours we hear people talk about antenna efficiency.
Can you please describe what efficiency means to you?
How can we measure efficiency and do a comparison between various antennas?
I am very cognizant of having a resonant antenna, but I don't know what specifically makes an efficient antenna.
Thank you very much, I am of course subscribed with notifications turned on and 73.
W3GUY
Awesome. Thank you
I do not wish to make a pest of myself but I do not know anyone I trust more for a clear understandable answer than you. My question is that after epoxying a 10 meter trap I find it is resonant at 9,100 when I had thought that it was resonant at 10.0. Since I can not adjust the coil I was wondering if I could just adjust the capacitance to bring the trap into resonance or if this would have some other adverse unintended consequence? Finally I have watched your videos at least 10 times and have not found anyone on youtube that does a better job and explaining things. best wishes Tom
Thanks Tom, no problem at all. I love this stuff, and I get to learn through all of your experimenting too.
I have not found that the epoxy itself makes a difference BUT any movement of the windings on the toroid certainly will. Be extra cautious in handling the trap until the windings are fixed into place.
Adjusting the capacitance is certainly an option. A small trimmer capacitor in parallel with a fixed capacitor could be a good way to make a tunable trap. Just make sure it can handle the voltage. It's a bit harder with fixed capacitors as they come in... well, fixed values.
Use a LC resonance calculator to backwards calculate your trap inductance based on the resonant frequency and known capacitance, then recalculate the capacitance you'd need with that inductance to get the right resonant frequency. Maybe you'll get lucky with a capacitor value that you have available.
Great video
After building two of these now I can say I am amazed how sensitive the tuning is. The slightest widening or tightening can make the SWR dip drastically off the chart. For me, I started by soldering one of the tails permanently to the capacitor then adjust the windings delicately to where I wanted. Then I soldered the other side permanently and retuned because if would out of tune after the soldering. After, ever so slightly widening or tightening to tune it exactly, I would keep testing to be sure it does not move. Once I am confident it will stay in tune I leave where it is (on the tuning wire still attached to the analyzer) not moving it and then drizzle the epoxy over the outer side of the toroid so wires lock in place. Later I come back with a bit more epoxy as a final coat.
Yes! Be careful with the epoxy too. I found out later that some epoxies have a significant impact on tuning which can be incredibly frustrating. Electronics grade silicone may be a better solution.
@@K6ARK That is bad news about the epoxying ruining the tuning. My 10 meter trap dropped to 10.06 Mhz but I called it good enough. I did not know such Electronics grade silicone was a thing I'll give it a try if in can find it. Even if the tuning goes off the rails a bit can't that be slightly compensated for in any way? Aren't we are still tuning the final wire length later so that the SWR dips in the portion of desired operating band?
The one question I did not hear you explain about traps is what makes them limited in power. Or how do you build it so more power could be used?
Outstanding explanation of how to build the trap!!
Looking forward to more great videos!
Good question, the capacitor is the primary power limiting factor. At some point, however, the current flowing through the wire on the non-resonant bands will become a problem for the thin wire and the small toroid. Larger toroids aren't particularly efficient on weight, so most use an air-wound coil as the inductor for larger traps for higher power. If you search around for info on trap building, I'm sure you'll find options like that for 100W and up. Other than the type of inductor and voltage of the capacitor, the concept is the same.
de Z33ST,
Great explanation as always.
Awesome video. I really like that you use the perf board for strain relief. I made my traps with the ws0ta PC boards and there is no strain relief except for the heat shrink over the ends. My next build will use the perf board. My experience in using the non-tinned perf board is that it helps to clean the Cu with steel wool or sandpaper for easier soldering. Also tune the antenna with the mast you will be using on the summit. The height of the wire will change resonance somewhat but the mast material will definitely change the resonant point for 40 meters. i.e. carbon fiber versus non conductive. Not by too much but still has an effect. de AI6XG
Great tip on cleaning the board first! I suspect a wipe with isopropyl alcohol would help as well. Will keep that in mind for the next go-round.
@@K6ARK Would there be any benefit to using double sided through hole tinned perf board with the SMD cap on one side and the toroid soldered on the other? Thanks
You could, but it makes it bigger. I like the strip of board in the middle of the toroid.
Excellent ❤
This is very helpful. I am curious about the capacitor voltage rating though. The trap represents the end of the antenna for the band, so it would also be at voltage max. Even at QRP, this could overwhelm 50V caps. I'm designing mine with 100pf and 150pf 1kv+ caps and t-67 cores, since that's what I have. The winds are reasonable (18-25 range) at that pf. The inductances are low (.6 to 1.6 for 10 and 14 mHz), and I am unsure if that's a problem.
Excellent video. Thank you for taking the time to produce and share it.
I have one question: at 13m:38s you used your AA-35 to test SWR. Could a NanoVNA act as a drop in replacement to do the same thing? Thanks again,
-rob
Very interesting video - thanks.
Can you use a nanoNVA in the same way as the Rig Expert for tuning the toriods i.e. looping the test cable through the centre of the toriod ?
Really impressive. How did you figure this out? Saved this video in my antennas playlist because I’m going to reference it a ton. Thank you for showing how you do it. I need to hang one of these outside a snow cave!
Just through learning about antennas and antenna design, looking at others' builds (like the SOTABeams traps), and then modifying to my own strategy. I fail a lot, and each time is a lesson. Note that some epoxy throws off resonance. Hot glue is likely a better potting compound. Even the heat shrink can have an impact. Resonance generally comes down in frequency, so tuning slightly high is probably best.
@@K6ARK Noted. Thanks for that. Anyway, your antenna projects are super cool.
Hi Adam, greetings from UK!
Great ideas you come up.
I have this project in mind to use some of your kits and ideas to build a backup antenna (trapped) for 20m and 40m that I could attach to a hiking pole (say at a max height of 1.6m) to be used if mast breaks or main antenna breaks or weather prevents mast deployment for example.
Of the three configurations your matching unit kit allows, which would you recommend likely to perform better?
I have a manual ATU that I could use with a random wire or to touch up a dipole or end fed halfway.
Great to have your thoughts on this.
Thanks.
Multi-Band single length Antenna! 👍
I feel like I learned a lot. Thanks! ~K6TJO
This is so cooooool.
BRILLIANT
The dust from your cutting and sanding of the PC board is bad for your lungs, take it out side next time. You have some really good and fun ideas and I enjoy your videos.
Thanks Nels! FWIW, I typically use a dust mask when cutting/shaping PBCs for that reason.
@@K6ARK oh, good, and thanks for the great antennas and videos
I really admire your micro builds. Your work is well done and the fit and finish is impressive for hand-built equipment.
If I want to run my KX3 at 15w, what toroid should I use? Will the T37-2 units be a little too small?
Those online calculators are pretty cool, but what if I want to use my hand calculator? Do you know where the calculations are documented? I might even write a program for my HP-41CX.
73 de AG7TX
Toroid inductance can be calculated by knowing the electromagnetic permeability, u (mu) and toroid dimensions. Typically, this is pre-calculated for a given toroid and reported as A sub L - the inductance per turn.
The LC resonance equation is on the calculator page - just scroll down.
I would anecdotally recommend a T50-2 size toroid for the 15w trap.
A trick you could try to widen your bandwidth back out on 40m is use the copper braid of some thin coax like rg-316 or rg-317 or even solder wick braid as your radiating element. The thicker the element diameter the wider your bandwidth is, why antennas like the Bazooka came into existence because cheap coax braid is easy to source.
The bazooka design includes elements that are more than just a larger radiator, and just adding a slightly larger radiator doesn't actually add much bandwidth. It comes down to the radiator diameter as a fraction of the wavelength. At that small of a fractional wavelength, even using a coax shield, you gain very little (negligible) bandwidth. Also, you add a great deal of weight and bulk which is what I'm trying to avoid in portable antennas. These trapped EFHWs can fit in a shirt pocket.
@@K6ARK the 21st Ed ARRL Antenna Book stated a Bazooka made out of something like rg58 (wanna say for 80m?) had ~14% greater bandwidth than a plain dipole. Still, even without the dielectric and conductor, 15 feet or so of braid for the 40m element probably isn't going to stuff in a pocket...
@@macgyver5108 right, but look at the Bazooka design. There is more to it than just using the coax shield as the conductor. I don't believe the OD alone contributes that much to the added bandwidth.
A note on capacitor voltage...
The 100v capacitor I used is marginally adequate for 5w. If you plan to run 10 or 15w, consider a 500v or 1kv capacitor to prevent over-voltage and breakdown of the capacitor. With the slightly larger capacitors, consider a T44 or T50 size toroid to ensure there's enough space for the capacitor to fit inside.
If you're going to be running 10-15-20-25 watts would you also need to upgrade the size for the matching unit's torroid to handle the higher wattage?
@@BB-mq3nn yes, absolutely. The FT50-43 is good for 5w for sure, possibly 10w. I have run 25-30w using a FT82-43 before it started to have issues. I run 100w using two stacked FT140-43. One would probably be sufficient.
Sounds like a good Quick Tips episode topic.
Adam - What package size are those SMDs? As in are they 1206, 0804, 0603, etc. Thanks.
I generally prefer the smallest I can find with the characteristics I want - typically 0603 or 0805.
Really enjoyable clear teaching! Learned a lot!
Subscribed!
73,
John - KK7JBZ
Brilliant!! ...wGOAT
@@wild-radio7373 what is hip?
🤜🏻👍🤛🏻
Hello Adam, I just found you by accident and I was captivated by how small those traps are. I was wondering, could it be possible to make a 160-10m long wire antenna using as many traps as needed for operating on all bands for permanent installation using maybe some larger ferrite and wires ?
Great tutorial 73 André VE2WNF
It would be nice if you showed the final result on your antenna analyzer. ;)
Thanks for the wonderful trap video. I am novice in the hobby and have stupid question. Can I use air core coil instead of toroid coil which has the same uH value?
Grate Video! I have a couple of Questions have you tested these at 100 Watts and what is the result.
have you considered using 2 traps spaced close together with small offset frequencies to widen the BW of some of the wider bands creating 2 or 3 resonant spots on a single band? thanks
so good
Hello! Great video! I can’t find the shoppinglist though?
I just ordered the parts. A trap dipole will be awesome with my KX-2. One question before I dive down the you tube rabbit hole. Can I use my NANO VNA to do a similar resonance check?
Thanks Adam, and greetings from across the pond. I’ve learned a lot, liked and subscribed. 73 de Steve, G0XAR
Very cool. Could I build these while substituting caps that are actually big enough for me to see 👀 🤔?
It's certainly possible, but you know me - miniaturize EVERYTHING. 🧐
could you use a multiple capacitors to get the right capacitance, if so are there any limitations?
Nice video.
73
Great ! Tnx !!
I FOUND IT!! haha♡ watching now :)
🤜🏻👍🤛🏻♡♡♡
I subbed So Fast!! Haha :)
🤜🏻👍🤛🏻♡♡♡
where in the band are you aiming to tune to? the middle? upper? lower?
If you were tuning your trap for the SSB portion of the band, would you still adjust it as low as your showing in the video? Does the amount change for other bands? Thanks for the videos and for all you do to help others.
The trap impedance is high enough even at the SSB frequencies to be effective there as well. 👍
That is awesome I have learned a lot today. If I want to scale this up to say 800 watts how big does the toroid and capacitor need to be? Thinking this may be good for the qth also. Thanks Jeff ke4fwe
800 watts with a 20 m torroid is problematic.... way too much voltage and amps on the torroid on the feed end, down right dangerous.
@@randyvanvliet226 good to know
Jeff, for traps on a QRO antenna, you are likely better off with an air-wound coil or a coax trap. More traditional trap construction methods will serve you much better. This is definitely a technique intended for QRP.
Question. I’ve tried building a couple of these but my SWR is sometimes close 1.5 to 2.0 when testing where the circuit resonates. Does a higher swr necessarily mean poorer performance? I find myself trying to spread coils to reach the ideal resonance; then removing a turn; then needing to compress the coils. All of this significantly affects the swr reading of the trap on my rig expert. Has anyone else had this issue?
Great video! Question, I have a MFJ-1889t. Could I build a trapped counter poise to use with it?
Trapped? No, but tunable? Yes... ua-cam.com/video/9yARhBgi020/v-deo.html
Excellent! Brilliant! What is the maximum Wattage these traps can operate at?
Thanks,
George - Alberta Canada
I would not exceed QRP power levels with them.
Alright Adam, what runway and airport is your QTH under? I hear a lot of takeoffs going on on this Saturday AM build.... LOL!, but only because my situation is similar, under KVNY 16 Right. Very impressed with how you trust, but verify everything in your antenna builds, for complete optimization of the whole antenna on all bands. What size torroids do you recommend if you want to build an antenna like this for a 15w capable, KX3 or KX2 version? The 50 T2's ?
Ha! I'm just South of KRNM in Ramona, CA, and anyone doing touch-and-gos or on an Eastbound departure fly right over. It's also our local CalFire base with 3 air attack aircraft.
For the KX3 and 15w, you may need to step up the matching unit toroid as well. An FT82-43 would handle full power better than the FT50-43. Similar suggestion for the -61 mix in the random wire option.
What bands do you want to use? If you want them all, the 9:1 with random wire is probably a better bet. But if you just want specific bands, the EFHW will be slightly more efficient. A 40m EFHW should tune easily (if you have to tune at all) on 40, 20, 15, and 10m even without a trap. Add a trap or link for 30 if you want. The T50-2 is probably a wiser option.
Haven't tried yet, but the KX2/KX3 might even load up the 40m wire on 80m.
Hi Adam, would you use larger gauge magnet wire with the ft 82-43 toroidal, say 20 gauge?
@@w6mrd900 I have used 24 ga for a 100w matching unit with no issues. 20 ga may be too big for an 82 size toroid depending on the number of turns you need. Smaller wire increases resistive losses, but with the currents involved here, they should be unnoticeable with even 24 or 28 ga wire.
Excellent instructional video Adam. Thinking about your 100v s.m. capacitors, I assumed they should be good for 25 watts, which is 44dBm or 100v pp into 50 ohms. (Maybe add a safety factor so as to not make thise little guys sweat, and not hit them with more than 10 watts.)
For a 100w capable antenna, 50dBm or 200v pp into 50 ohms, you'd want 250 or 500v rated capacitors?
Or am I forgetting the impact of the impedance change between the antenna socket at 50r and the feed point impedance of the rig end of the half wave wire, around 2.5kohms?
In other words, what's the RF voltage swing across the traps (this has to be known at all frequencies of operation), and how should we use that to size the capacitor voltage rating for various power levels?
I am a mechanical engineer so take my "wisdom" with a grain of salt, but I believe the voltage is higher at the ends of the EFHW (voltage max/current min) and therefore you need a higher voltage cap to prevent arcing across the dielectric.
For efficiency and power handling on a 100w antenna, I'd probably go with more traditional air-wound coils rather than toroids. I suspect these little toroids would become saturated at > QRP power levels.
@@K6ARK Thanks Adam. A good option for portable QRP, but maybe use the linked dipole with the 100w rig. Once you go to air wound inductors they get big and bulky, OK for a fixed installation that can be heavier duty.
Yes, I still use the linked dipole as my standard for 100w portable ops.
Before I go crazy and build a trap for every band up to 40m, dare I go 80m? I should ask, how many traps are too many? Currently I've built one for 10m, 15m, 20m, and 30m. I understand that the antenna will be less efficient with the more traps that I add, but I'm thinking of also doing 12m, and 17m. Any advice, or just send it? I am using 24AWG magnet wire and T44-2's with some nice 500V rated mica caps.
Adam, thanks so much for all you have done for the QRP, DIY folks. Your videos are detailed and very well done. I do have a question, in ordering parts for the micro-traps I used your link to perforated prototype board and ended up with a perforated bare phenolic board, nothing to solder to. Do you have another link to the correct pcb? Again nicely done. Tom KE0JVS
Shoot! Sorry about that. I do indeed use boards with copper for soldering. I selected the wrong link for the list. Here's what I would suggest ordering: amzn.to/35lcvzn. I updated the list in the description as well. Again, sorry about that, and thanks for the comments!
@@K6ARK Thanks, you are Mr. Johnny on the spot. 73 Tom
Ha! Just tryin' to share the love of tinkering and ham radio. Hope you have fun with the build!
How can I calculate what tyrods and capacitors, magnet wire I would need for traps to use with 100 watts? Is it even possible?
Great stuff! What would you recommend for 70cm and 2meter handheld yagi antennas, 10watts?
Interesting question. I have never designed traps for VHF and UHF. Tell me more about what you're trying to build.
An end fed half wave antenna should be capable of multi-band operation without the traps. Certainly a 40/20 meter antenna should work without traps, though it would be optimum for the CW part of 40, and phone part of 20. With a simple antenna tuner you can cover all of both bands.
I cut pc board with a jeweler's saw.
Correct. The traps or a link add 30m. Note that the antenna may be resonant slightly above the 20m band as a result of the antenna being closer to the ground in wavelengths on 40m, making it resonant on a slightly lower frequency. As you noted, this can be resolved with an ATU. Alternatively, a strategically located coil can add inductance that brings both bands into perfect resonance.
@@K6ARK Years ago I made a multi-band trap dipole for 80,40, and 30 meters. I used air wound coils and ceramic door-knob caps (5kv!). The caps came out of an old ART13 WWII transmitter, I measured their values using a Time Domain Reflectometer when I was working at Digital Equipment Corp. I adjusted the trap frequencies with a Grid Dip meter (home brew) by adjusting the turns, fine tuning by spreading out the last turn on each end of the coil. Then I tuned the outer ends of the dipole for each band for lowest SWR. The antenna was raised and lowered several times to add the additional parts for each band in turn, first 30, then 40, then 80. Took all day! (BTW it was a tower mounted inverted V).
excellent tutorial. Question: is it possible to check the resonance of traps without an antenna analyzer?
The other (actually better) option is to use a Vector Network Analyzer such as a NanoVNA. I guess theoretically you could achieve the same with a signal generator and oscilloscope, but that would be a much more costly solution. Without some kind of measuring device, you will not be able to tune your traps.
@@K6ARK Adam, with a signal generator and o'scope, how do you determine resonance? Thanks in advance. Jerry
why are some traps wound around pvc pipe and others like yours are wound around ferrite cores? I don't understand the differences or why one would choose one method over the other. I love your videos and thank you for sharing your knowledge and skill. 73's Tom, W1TWS
Tom, air-wound coils work fine as inductors too. They require more turns to get a given inductance and are more susceptible to interference to/from other nearby circuit components (not so much of a factor in an antenna, of course). I choose toroidal inductors for my traps because of the nice small size. You can certainly accomplish the same thing with an inductor wound on a cylindrical form.
Should a 20 meter trap be resonant at the low end of 20 meters (14.0) or should it be resonant at the high end of 20 meters (14.350) , thank you Tom, W1TWS
Tom, I don't know for sure, but I understand that the traps incur a bit more loss if they are right on the frequency of use. I have heard recommendations to tune them slightly below the desired frequency, but I have seen or heard a legitimate explanation as to why that's better than slightly above. One final note is that these micro traps are relatively narrow-banded. If you plan to operate CW and SSB with the same antenna, it might be best to tune it to the seldom-used 14.100-14.150 range. That would put it just above the CW portion of the band and just below the SSB portion.
Excellent build instructions! One question though: Since an EFHW is resonant on harmonics of whatever frequency it is cut for, should it not be possible to do away with the 20m trap and just have one for 30m?
No, unfortunately the 30 m trap throws off the resonance on 20 m because it provides more inductance and loading on 40 m then it does on 20.
You can, however, use a link for 30 m and then just use the full 40 m half wave for both 40 and 20 m
@@K6ARK perfect. Those traps are too cool not to build so I'll go with your original plans 👍
Adam, what's the thinnest wire, I have tried 26awg and works perfect, now I am going to try , Surfstrand Copper Trolling wire, 30lbs, .028 in (0.71 mm) dia. 600ft is $30
Robbie, I actually use some 30 ga stuff for some of my ultralight antennas. It's very fragile so you have to be very careful with jt, but I have a trapped 20/30/40m antenna I have been using with the MTR3B for over a year. Still holding up! It's single-stranded so if it links, it'll probably break. But at $9 USD for 1000 feet...it's not going to break the bank. amzn.to/2FLCjdL
My 12-year-old daughter is a General, and I got her a 705. I'd like to see if there is a chart somewhere with wire sizes, and torrid sizing with losses etc. I know she will be using JS8Call as well as CW and SSB, she is learning CW now, and my 15 yr daughter is running 15wpm. I was planning on 20w to give a little head room. Does anyone know of a chart or have recommendations? Kids will do all the work on the build.
Your analyzer sweeps very quickly compared to my AA-230 Zoom. Do you know if that is the nature of those analyzers or did you adjust a setting to get it to weep faster?
Hmmm, I didn't adjust anything. I'm not sure if there's a setting or if it's just a difference among models. Mine is the AA-35 Zoom.
Hi Adam,
You mentioned having a matching unit for each band of the EFHW. Are you using those small bullet connectors you showed in the linked dipole video to swap out each matching unit when changing bands? Stay safe. 73 WJ3U
No, I typically just tune the matching unit to the middle of the set of bands I want to operate on - so, for example, I'll tune it for 30m for a 20/30/40m antenna. You'll experience slightly higher swr on 20 and 40m but it's plenty good enough on all the bands. It's more a matter of optimizing the matching unit for the primary bands of interest than it is a requirement. Finding the right capacitor may be a greater factor if operating on the higher bands or with a multiple-half-wavelength long antenna (i.e. 15m on a 40m halfwave ).
@@K6ARK Thanks Adam.
Is it important to use a SMT cap? what kind of thru-hole cap could I use instead?
Great! Question: Obviously when using these EFHW antennas, the other side of the antenna needs to exist... what do you use as a counterpoise? I've seen some people claim an EFHW doesn't need one, which seems like nonsense to me. What's been your experience, Adam?
Because the feed point of an EFHW is high impedance and low current, much less of a ground/counterpoise is necessary. I have found that the radio itself and it's capacitive coupling to the ground and to you seems to be sufficient. These EFHW antennas perform very well, and I am regularly able to work DX with them on 5w CW at QRP power levels. I see noticeable difference in performance between the EFHW and a dipole at similar height.
@@K6ARK Thanks Adam. What works in the field is what matters, and the capacitive coupling idea you mentioned makes a great deal of sense to me. In addition to the no-counterpoise approach, I may play around with the Steve Yates AA5TB 0.05 to 0.10 wavelength counterpoise recommendation, too, since ground mineralization (and possibly therefore capacitive coupling with the ground?) in OH is far different than in the desert of the West (I know from working QRP out there is early 2020). I of course will also try your no-counterpoise approach just to see if I can discern any real difference in signal output using the RBN or possibly a field strength meter. Thanks again for your input, and for the great work on these videos! 73 de KD8ZM
Great job on the traps, thanks!
AA7OY