NOTE: DO NOT CUT YOUR ANTENNA WIRE FROM THE END OF THE WIRE. Measure from the auto transformer to the desired length. This is because you may not have exactly 75ft of wire. So if you cut from 75ft to 65 feet, you cut 10 feet. However, since the kit is approximately 75 feet, you may cut short. Makes sense? Cool. email me with questions or concerns. Other mentions regarding the video: LENGTH. I am aware that the calculation for the half wave is L=492VF/F or (492x.97)/F. If F = 7mhz ... L=(492x.97)/7.000 or L= 68.17714285714286FT for the EFHW. Although I recognize this is the correct way of learning. This will be something fun to go test in the future. I have wire with a known velocity factor and we can see how close the numbers are as my EFHW is more towards 64.5-65 feet. I will test this because I am very intrigued with what I have done vs the math that is mathematically accurate. KB6NU has a writeup over here: www.kb6nu.com/dipoles-shorter-half-wavelength/
The resistive effect of inductors and capacitors is called reactance. They react to the magnetic or electric fields, and this recatnace is frequency dependant. Inductive reactace is positive on the smith chart, capacitive is negative on the smith chart, hence inductive reactace = 2 * pi * Frequency(Hz) * Inductance (Henry) and capacitive reactance is 10^6 / ( (2 * pi) * Frequency(Hz) * Capacitence (micro Farads)) -- this is 10^6 because of the conversion to microfarads. Regardless you can see this in your nano vna by finding the resonant point on your antenna and tunning slightly above and below it, the reactance+/-johms will flip polarity between inductive and capacitive depending on if you're tuning higher than the resonant point (capacitive) or lower (inductive). You can "tune" any antenna to react at near a 50 ohm load with the right amount of added reactance. This is precisely how an antenna tuner works, but it's far more efficient to do it at the antenna ;)
Well done Sean. K6ARK is 100% correct. His answer is succinct. It is the ground below the radiator that adds capacitance between each end of the EFHW and that effect pulls the resonant frequency away from what the wire is cut for. The PROBLEM is that height above the ground changes for each band, and therefore so does the amount of capacitance between each end as influenced from the ground below. We can NOT use a tuner here because it would likely saturate the UNUN core, so making the wire "resonant" on all bands is the only way to go. 73 & keep up the great work.
I’ve got compensation coils on all my EFHW builds to bring in the higher bands…but I just use plastic pipe or conduit and drill it out. That 3D print is awesome….by far the neatest way to do it. 👍
Hi Sean and thanks for the video! I´m using a coil with 4 loops at a diameter of 5 cm (1,97 inches) about 2 m (6,5 feet) away from the 1:49 transformer and it works perfekt at all of the 4 bands. 73, Bernhard
Thanks for the video. My EFHW was put up to be a fast and easy temporary antenna when I first moved into my current home. It has worked so well that it has become a permanent and primary antenna. I'm in no hurry to take it down or replace it. Just a thought...I haven't experimented very much to be able to prove this...but I think if you make the antenna around 135 feet so that it is a half wave for 80 meters then it may bring the resonant points more in line with the higher frequencies. Also, I have cut the wire exactly half way and inserted a capacitor. That seems to help drop the resonant points right close to all the bands 80 - 10 meters.
Thanks for the nice down to earth presentation. I used an inductance and a short piece of wire at the end of my 40m efhw to get into the 80m band. I am lately experimenting with coil/capacitor traps on the efhw. Using a homemade, printed circuit board to mount caps on. Pcb again fits inside a piece of 20mm pvc conduit with the coil wound on the outside.
Thank you for using a VNA display to graphically display the changes to the antenna response to the coil. While the results can be numerically expressed, the graphic display is helpful.
Excellent. I like that there simple that can make a difference. Just got your antenna kit this week. I'll look to build as soon as I can find an hour or so to get it done. 73, KN4VA
@@HAMRADIODUDE I have seen a similar solution but with the capacitor on the other side, 6-7 ft from the end of EFHW, so if you cut too short. You could say it was on purpose. :D
@@HAMRADIODUDE, the only issue is that the coil extends the antenna, and the capacitor shortens, so you will need a longer attachment. The positive is that the bandwidth should be wider. I wonder if this is the way to cover 80m, not just the piece of the band.
Right now I am building an 80m-10m EFHW using the fairite 2643251002 core popularized by Colin-MM0OPX. After rough tuning at a QRP event without an inductor I added a 9-turn inductor on a piece of 1/2in PVC. I removed one turn and adjusted again. The transformer is close spaced and tapped for 49:1, 56:1, and 64:1 with a 120pf capacitor across turn 0 and turn 2. The problem I am seeing with both 8 and 9 turns is on 40m and 20m I need to electrically lengthen the antenna to get the lowest SWR into those bands. At 15m and 10m I need to shorten the antenna to raise the minimum SWR dip into those bands. On 40m and 20m I need more inductance. On 15m and 10m I need less inductance. I am considering using a larger diameter PVC former for the inductor. Most of the commercial units use 3/4in PVC or larger up to 2in O.D. For a portable antenna on a wider like I am building smaller diameter is better. Ideally I am trying to optimize for 3.94mHz which makes the job more difficult when also tuning for higher bands. 3.94mHz is of primary interest because of regional National Phone Traffic System nets and ARES nets that would be useful after a hurricane. Also, I am considering switching to a 150pf capacitor. I understand this increases the resonant frequency of the antenna and can improve efficiency on 10m. I don't know how whether the increased capacitance provides a uniform increase in frequency or more towards the higher frequencies. I know adding inductance has greater effect as frequency increases. I suspect that making the inductor larger diameter may increase the inductance per turn, but with fewer turns there will be less relative inductance between 80m and 10m. I may have to be satisfied with having 3.94mHz within the 2:1 SWR and near SWR minimum. Do you have any insights to offer?
I have had some success with an 80m EFHW that was also able to resonate in the higher bands. Technically, I would call it a linked EFHW. I started with the wire and coil described in this video. Then essentially made a second wire with a coil. Then I linked the two wires together by the ends opposite the coils. Put it up in an inverter V and it did not resonate in the portion of 80 that I was interested in so I actually had to add some wire to the end with second coil and that got me to the region of 80 I was targeting. But the dips higher up were just above the bands they should be in. So I added more turns to the second coil (it original had 11) I think I ended up adding 6, but YMMV and that brought the SWR dips back up into the higher bands
I slightly modified my comment above to better describe what I did. I do want to redo this with some more wire that I should arrive in a few days. I will try and take better notes on how I do it.
@@HAMRADIODUDE Probably 64 ft + six inches give or take. Anything longer dropped 40 and 20 resonance too low. It's the TennTennas xformer which works great otherwise. I just noticed the Myantennas EFHW-4010 uses a 63 ft radiator + a coil. Tho using a 56:1 xformer (!!)
Hey Sean, great video! My recent problem is with an inverted L random at 84' with a 50' coax using shield for counter. All was good until the LDG 9:1 started giving me intermittent issues with an open circuit. Fast forward to today and it's been a week of grief trying to utilize another 9:1 a guy made for me last year. I've been trying to build my own Unun but parts are scarce like Adam's toroid for the 100w kit. Nothing will tune now and Im physically exhausted from changing out feedline and etc... The strange issue now is that unscrewing the UHF connector from the radio with just the center pin left connected restores the signal. Back to square one and start over I guess. Id like to add you coil but Im using 14 THHN wire. I need to start with a new 9:1 kit and check everthing I suppose. Thanks for the good video. Any suggestions welcomed.
Did you add extra wire to the antenna to cover the lemgth used in the loop - or did you make the physical lenght slightly shorter after winding a bit on the coil. BTW, the excellent Chameleon LEFS 8010 have about 6 turns on the coil, length of the 40-10 meter part is 63 feet + 67 feet for the 80 m extension
Great question. To answer your question, after tuning for 40 and adding the coil, I did not have to add wire the coil shortens the antenna in that aspect. I did have to add wire initially because I originally cut too short for 40 (mistake on my post part)
Hey Dude, its been a minute. Marconi and Tesla used trapped end feds. As many 7 traps in a single sloper. EFHW is just one section of the OG Trap Antenna. Using the EFHW, make an inverted V, or inverted L. The magic numbers are, 12 and 1/12
Would the intuition that an inductor will behave as an open circuit from some frequency onwards help? I think after your implicit reference to the inverse relationship between length and frequency, that intuitive analogy might help.
I have this efhw 80-10m antenna in average 5 m above the ground with a 110uH coil to make it shorter at 80m. No counterpoise. SWR in average is 1,5-3 and with an atu I get it down to 1,0. What is really strange is when I add the counterpoise. Seems to mess up 17m... atu will not match it. When I remove the counterpoise atu is able to match 17m again.
Hey there, sorry to have a late response. If you purchased this EFHW from me, please contact me through etsy so as to get better service, in a quicker fashion. Etsy allows me to interact with customers, look up customer information, and provide support.. Otherwise, what wire are you using, what length counterpoise and antenna wire and where does it show resonate on 40, 20, 15, or 10 (or as close to it as possible) with and without the Counterpoise? Cheers.
I have always been told the capacitor is for the upper bands on the EFHW with 49:1 UNUN I wonder if anyone has tried an adjustable cap to see if it will tune in the upper bands.
Hello, there. Did you purchase a kit from me? If so, shoot me an email. In short, you start rapping about six feet from the actual auto transformer or the toroid. . If not, which toroid, are you using for your efhw
Thanks! Today I am going to jump into 80m. I think the coil will be key to making this work with 80 as well. the 7mhz may be the key factor here (shoot for that to start).
