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HAM RADIO EFHW Mystery Coil. Do you need it and is there a better alternative?
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- เผยแพร่เมื่อ 28 ก.พ. 2022
- That little coil that sits at the end of some commercial designs for the EFHW. What does it do and do you really need it? Maybe you don''t. Peter G3OJV takes a closer look and lets you decide.
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👍Thanks for video. One method I have used to find required capacitance value is a small variable capacitor. Adjust this to get things right on analyser. Once happy, remove it and measure the capacitance. Then make up the capacitance using fixed value high voltage components. I also have some experimental coils that can be tapped at different windings to make crude variable inductors. Similar to capacitor idea, these can be measured when adjusted for optimum readings and permanent fixed inductor made.
Hi Steve, thanks for that. 73 Peter
Clear explanation; one comment, though. The capacitor's impedance depends on its value and the frequency, so it doesn't appear as a short on the high bands. It's located at/near the center because that's a current maximum at fundamental (and odd harmonics, like 10.5 MHz on a wire cut for 3.5 MHz), but a current minimum for the even harmonics (7, 14, 21, and 28 MHz). You'll need a very high voltage capacitor here, because it will be located at/near a voltage peak on those even harmonics.
Peter you are so right ham radio is a fiddling hobby. I am constantly fiddling with my different antennas to see if I can make them work better and that is a real joy to me when I’m successful.
Thanks for the clear explanation. It really helps me understand the design alternatives.
Peter, a choice you did not mention was adding a choke (not trap) at the end of a 40M efhw and adjusting the tail past the choke to the 80M frequency of interest similar to the Shorty 40 design but for 80M. You get a shorter antenna length, can adjust by adding or removing wire turns or adding or shortening tail length, and you do not have to chase down a selection of costly high voltage caps. Your thoughts. I enjoy the channel. Stay safe and 73 from the Great Lakes State of Michigan USA. Doug, K8QDP
Hi there. Great to hear from you. I did not mention it but like the 40-10m version, the coil is not needed. i have done several videos on the 80m choke version. 73 Peter.
I own a My Antenna's EFHW 40-10 antenna. It has the coil and tunes 40-10 meters practically flat across the CW portions of the bands. A little higher on 10 meters.
Nice explanation 👍👏👏
Added 17 and 12 meters to my 4btv with the attached wires. Also put the 30 m resonator on it so my 4 btv works on 7 bands. Well, cant seem to attach the picture
Peter, if the coil is 1.5 uH, would not a clip-on toroid of equal value work as well and be much easier to add-on and adjust? Thanks.
Very interesting Peter. Thanks for the video.
Glad you enjoyed it
Thank You very much
Enjoyed this video and also the others you have. Thank you. Agree with your sentiments on Ukraine and congratulate you for bringing it up. Like the other gentleman I also feel sorry for the ordinary Russians whose lives are squandered. 73's VK5WB
Excellent info. as always Peter, one question, does adding the coil affect the the length of the 80m element?
In other words, do I add enough wire to make the coil, or just use the existing length and wind up being a bit shorter?
Thanks...
Can anyone advise if I need to make my 80m wire longer by the amount of wire used up making the coil?
You can put a trap in a efhw antenna?
Excellent video. The explanation of the harmonics is really not accurate in that they do not multiply out as you stated, For example, a 80 meter might have it's lowest SWR at 3.55 MHz but it's 2nd harmonic may be 2.1 X 3.55 or 7.455 MHz and not 7.1 MHz depending on many factors. It will be a day long project full of decisions when tuning an EFHW. Decisions like "With a 470 pF cap I raised my 80 meter sweet spot to 3.7 MHz but now my 20 meter low SWR is now at 14.30."
I suggest getting it as close as you can by experimenting and use a tuner to ensure reflected power is re-radiated and a high quality coax like RG213 to reduce cabel losses. If you can get all band frequencies below 3:1 a tuner will enable you to radiate better than 90% of your power.
Hyend Co. have an 8 Band 800 Watt with the inductive coil arrangement and the high voltage capable capacitor. With the 40m wire stretched at 12m (Spiderpoles), in my location, it has been a winner for the past 3 years. Maybe we should also spare a thought for the ordinary Russian people who, I suspect, have been fed a different flavour of the truth.
Many thanks. 73 Peter
Great videos Peter.
The Dec 21 CQ mag has an article on the capacitor adjusted EFHW. I built an 80m EFHW cut for 3.550MHz and added a capacitor about 30% of the way from the unun. I put a plug and socket on the capacitor so that I can short it out if I want. The capacitor also has a 1Mohm static bleed resistor across it. The antenna has a SWR of less than 2:1 on all bands except 10m, where it just goes over 2:1 on some portions.
Cheers
Jim
Thanks Jim. Interesting imfo. 73 Peter
Hi Jim. Did you reduce the ratio to 36:1 as per the article or stick with 49:1? 73, John.
@@johntyler4222 stayed with the 36:1 ratio. It worked well and had good SWRs across the bands. 73. Jim
@@jimreed6503 Thanks for that Jim. 73, John.
Stop war!
Educational indeed!
I need to do some testing, but with my MFJ 80-10 End Fed, I'd like to be able to set the 80m portion at 3.939 (ARES stuff), then the center of the General Class phone band down the line...anyone have a recommendation how to do that...
Great video !
Thanks!
I talked to so many operators in Ukraine... It's heartbreaking.
Agree. 73 Peter
Wonderful way to start a videos!
Many thanks.
Tnx for the tribute to the Ukraine Peter...at least you can see all of Peter when he talks, some of these guys use giant no doubt $$$ studio mics that cover half the guys face... is there some sort of cachet to this? A simple lapel mic seems to work just as good. The video, in fact most seem to cover the EFHW configured in a L shape ... hopefully the same will be for a straight line which is really the only practical option I have... now use the 110mh coil at the far end version, now gonna try Peter's 5 turn version at 2 meters fed with LMR 400.
Very good explanation. Thank you. 73 PA5BAS
You appear to be a doppelganger to Jeff Dunham's "Walter".
Anyone else notice that, such as at 4:18?
VVV
Good job on the video. I always learn some new fact about our hobby. We should all pray for the people of Ukraine. Unbelievable horror.
Thanks Frank. 73 Peter
What is the gain of a HWEF antenna? One website claims that it is 7 to 10 dBi.
On the base vand there is zero gain. As you operate on higher bands there is a small gain as lobes increase but more like 2dB!
Where does the coil go again. We need some practical examples of both.
2m in from UnUn as I described in video.
@@watersstanton 2m on the antenna wire? Not the coax. I was sure that the coax feed was a part of the antenna. I've not seen this before. G7VFY
On the antenna wire, 2m from the matching transformer.
It is actualy 6 turns the 2 half turns at each end make a full turn.
Thats the basics of air core coil forming 2 X half turns = 1 full turn.
Interesting video that I already known about but interesting all the same.
If you are referring to the coil in the video it is most certainly 5 turns.
@@watersstanton Yep you are correct I counted the center turns first as 5 for some reason
Thanks Peter m0udb
👍👍......................
Ukraine is on all our minds …peace
Agreed
You don't know, what you talking about Ukraine. You are unconscious.
Thx n4jrs 73
Thanks.
Great explanation of the hwef I built antennas for both my friends and they love the antenna and now I can make them a new one thankyou look forward to the next.Dylan 🫡🏴