The QRPer Board

Hi Folks, please excuse my ignorance on this but several weeks ago Tom did a review/activation on the KM4CFT EFHW/EFRW antenna kit where he was able to activate most of the bands from 40-10 using this antenna kit with a 30M and 40M link. He was able to to use the 30M wire to activate 17M. I currently have one of the KM4CFT kits but I had a Tenn Tenna Mini 49/1 not being used so I decided to use that to duplicate the process with it. I have completed the 30M link and it tunes beautifully at 1.04: but does not like 17M at all. I will continue with a 40M link but am puzzled as to why to 17M does not work --- resonant fqcy was well above 17M
Any thoughts as to why I am having this problem?? Many thanks!!
Mike Serio
KG4MTN

KG4MTN wrote: ↑Fri Jan 12, 2024 12:54 am Hi Folks, please excuse my ignorance on this but several weeks ago Tom did a review/activation on the KM4CFT EFHW/EFRW antenna kit where he was able to activate most of the bands from 40-10 using this antenna kit with a 30M and 40M link. He was able to to use the 30M wire to activate 17M. I currently have one of the KM4CFT kits but I had a Tenn Tenna Mini 49/1 not being used so I decided to use that to duplicate the process with it. I have completed the 30M link and it tunes beautifully at 1.04: but does not like 17M at all. I will continue with a 40M link but am puzzled as to why to 17M does not work --- resonant fqcy was well above 17M
Any thoughts as to why I am having this problem?? Many thanks!!
Mike Serio
KG4MTN

Hi Mike,

From my understanding and experience, EFHWs are resonant antennas, and they work well on the base band and its harmonic multiples. So a 40m EFHW works acceptably for 40m (7 MHz), 20m (2x7 MHz = 14 MHz), 15m (3x7 MHz = 21 MHz), and 10m (4x7MHz = 28 MHz). 30m (10 MHz) is not a multiple of 7 MHz, so a link is used to shorten the radiating wire to a resonant point. 17m (18 MHz) is neither a harmonic multiple of 7 MHz nor of 10 MHz, so I have always used a second link in my linked EFHWs to get 30m and 17m.

One nice thing about using an EFHW on resonant bands is that a tuner is not needed. With that said, I have also successfully used non-linked 40m EFHWs with a wide-range tuner to work on every band from 80m to 10m.

Best 73 de Brian - K3ES

Thanks Brian, I thought I would have to use another link in the chain to make it work well. Building an EFHW specifically for my TR-35, wanted to be tunerless.
72 and stay warm!!
Mike KG4MTN

Mike.
I built up a 40/30/20m trapped efhw using the sotabeams pico traps available from DX Engr. also have a linked 20/17 m efhw . garden variety 32 ft telescoping mast is used for support ;both work great with tr35 for pota ops.
72s de randy

The real question is, "what is the rest of your system?" What kind of radio are you using, and do you have/plan to have an antenna tuner?

Like Brian said, a 17m and 30m are going to play well together on an EFHW unless it's built for 80m (multiples of 3.5 MHz). If you want just a 40/30/17 antenna, a trap EFHW is a good option. If you want a simple 40/30/20/17/15/10m EFHW, I go with a 40m EFHW (about 66 feet) and plan on using links for 30m and 17m.

I have built several EFHWs, including a couple with traps to meet the requirements of my radios. I've found that an EFRW is a great "no worry" antenna if you have a tuner. I use a 35.5 foot antenna with a 17 foot counterpoise for everything from 10 to 40m with my FT817 and (tr)uSDX.

73,
Mike, KL7MJ