After watching another video about the EFHW 40m antenna, (video - Utah Amateur Radio Club, 13 January, 2002 UARC Meeting) someone modified a 40m antenna to "center" the SWRs on each band by adding a 200 pfd silver mica capacitor at a point about 40% down from the 49/1 unun. To make sure the voltage didn't build up in the wire, he added a 33k resistor across the cap to bleed off any excess build-up. So you might consider adding a resistor to that end cap to do the same thing.

A balun is a device that balances the current between the outputs. This is a transformer with only one output therefore it is not a balun. Technically it is a transformer. The term "unun" is acceptable also since it's output and input are both unbalanced.

Thanks Dave. Appreciate the very nice update. 73

Love this antenna! So glad you are doing this series!!!

Thanks!

The antenna lengthened to 80 meters may also give you coverage of the 30, 17, and 12 meter bands. It will have additional resonant points at 10.5, 17.5, and 24.5 MHz (approximately), and those may be close enough to provide an acceptable SWR. I'd like to see tests of that.

Could you start off with a 80 EFHW and add a capacitor, some wire and take it to 160 meters?

There may be a Cap that will move the frequency to cover more of the low end below 3:1 so FT8 can be done with the tuner in the radio without loosing the high end.

@joeb3300

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That's what I am going to try - I need the digital end (THOR22, etc) AND the top of the phone end for NJSP digital and phone EMCOMM nets.

Why not just add less than 66 feet of wire if you want it to work on 75 meters?

My son has a farm. My small city lot is to small for this. Thanks, Dave. N0QFT

Good grief Dave! I hope that solder job at 10:19 was you testing it and not a permanent set up. Looks to me as soon as you tension the antenna, the wires you have on the insulator will pull taut and the cap will be pulled apart. Nobody should duplicate this assembly work as depicted.

I got my 40-10 EFHW to work on 80m with a 100uh extension. It was a piece of 2" PVC with 100? or so winds and then a few feet added to that. I'd have to check the exact values but it wasn't very hard and didn't add more than 6 feet.

@n4lq

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The addition of the coil near the far end works to an extent but your SWR isn't very good on 80m due to the lower impedance it creates. Also the full length 80m version easily covers 30, 17 and 12m which the loaded version does not. I've found that a poorly installed full half wave version works better than a nicely installed short version.

Dave, thanks for the video. You mention at 10:11 that the capacitor leads are very thin, and you are concerned about their current-handling capability. Instead of using one 470pF cap, you could have put three 150pF caps (or five 100pF caps) in parallel. That would give you close to 470pF but with roughly 3x - 5x the current-handling ability. [IMO the current isn't going to be that high.] I'm hoping to try this when I have an EFHW antenna set up for 13 May's AFD Crossband exercise. KB2JSB

@n4lq

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The current is going to be "that high". The capacitor is located at the highest current portion of the antenna on 80 meters. A typical capacitor of 3kv or higher usually works fine but I used a doorknob capacitor since I run legal limit at times. Don't skimp.

What mix toroid is used in this kit?? and how many stacked together? Thanks Dave for another great video

I'm using an 84' EFRW with a 9:1 UnUn. From 15. MHz to 54 MHz it peaks at 2.4 SWR just below and above the full 80/75 M band, about 2.2 in the middle. It's below 2 through 160 M and above the 2.4 peak at 4.4 MHz all the way to 54. I'm getting these numbers from a screenshot of a NanoVNA Saver sweep, so some of the numbers aren't exact. My external tuner has no problem anywhere, and I think the internal tuner could probably handle all of it but I haven't tried. Did I just get very lucky with the placement, counterpoise, and loops through a toroid just before the lightning arrestor?

@n4lq

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This is a sure indication of a very lossy antenna system.