Linked End Fed Halfwave Antenna

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KN3A
Posts: 29
Joined: Mon Jun 06, 2022 11:42 am

Linked End Fed Halfwave Antenna

Post by KN3A »

The other day I watched a video of a YouTuber making a linked EFHW. I decided to make one myself using his method in the video. I am not good when it comes to soldering, so I thought this would be a good time to practice. So I used my spark plug and created a linked EFHW for 20, 30 and 40 meters. Then I tried it out (I had the 20 meter section closest to the spark plug). Did a SWR check and all was good.

Once I was finished I started thinking to myself, how is this really going to help me with having a linked EFHW? I know there's definitely advantages with dipoles, but not sure what real purpose my linked EFHW does.

Comments?

Scott
KN3A
Brian - K3ES
Posts: 93
Joined: Fri May 27, 2022 12:55 pm
Location: NW Pennsylvania

Re: Linked End Fed Halfwave Antenna

Post by Brian - K3ES »

Hi Scott,

I build and use linked EFHWs for QRP POTA activations. I also started my QRP antenna building with a linked dipole. All of my base antennas to date have been based on 40m (so nominally 66 ft long). I prefer the EFHW design to the dipole for 3 basic reasons. First, the EFHW gives me multiple resonant bands without links, just based on harmonics (i.e. 20m, 15m, and 10m resonate on a 40m wire, because 40m/2 is an integer multiple of 20m/2, 15m/2, and 10m/2). Second, the EFHW is generally simpler to deploy than a center-fed dipole (I use an inverted V configuration with the apex at a convenient point along the length of the wire, or even as a sloper). Third, the EFHW can be run with a much shorter feedline by placing the operating position near the feedpoint (a dipole requires the feedline to be at least as long as the feedpoint is high).

I use links in my EFHWs to allow me to make the antenna resonant on bands that are not harmonically related to 40m (e.g., 30m, 17m, & 12m). By opening a link, the antenna can be used on another band without needing to resort to a tuner. By the way, only one link change is needed for the EFHW, in contrast to a centered dipole where a link must be broken in each of the two legs.

For my TR-35, I built a linked EFHW that gives me a single antenna that can be made resonant on each of the transceivers available bands (40m, 30m, 20m, and 17m, using 2 links). For my TX-500, I built a linked EFHW that gives me a resonant antenna for 40m, 30m, 20m, 17m, 15m, 12m, and 10m, using 3 links.

I hope this is useful to you.

Best 73 de Brian - K3ES
SkipRD
Posts: 60
Joined: Fri May 27, 2022 12:58 pm

Re: Linked End Fed Halfwave Antenna

Post by SkipRD »

I also have a linked EFHW, although I'm basically a slacker and went for the minimalist version, mostly because my Venus SW-3B only has three bands (20-30-40m). So, I have a 40m (66') EFHW, with one link at 49' 3" for 30m. That gives me all I need for now, and even with that I rarely pull the link and get on 30m. In fact, when operating solo I've always gotten to the end of my operating window on just 40 and 20 without going to 30. I've only pulled the link and used 30 once when there was another station with me and it was on 20. Even still, having 30m is a nice option in case there's a contest or something and I need a WARC band to find some clear air.

When I get (if ever) my KX2, I may add another link or two, or just go with a random wire and use the tuner.

So, to respond to your question (does a linked EFHW really help all that much?), I guess the answer for me is, maybe. Sometimes. A little. :D

73 Skip K4EAK
N8TGQ
Posts: 78
Joined: Tue Jun 21, 2022 5:06 am

Re: Linked End Fed Halfwave Antenna

Post by N8TGQ »

I use the original MTR-3b when out in the field, which also only has 40, 30 and 20 meters.
I'm even more if a slacker than Skip. Instead of putting a link in my EFHW, I tied a knot at the 30m resonant point, and wind the wire out to that length.
The winder is made from an old gift card, and has notches I can use to lock the wire at any point.
It"s a bit more trouble to change bands, but there's nothing to break or get snagged in a tree.
I usually start and end an outing with 30m, since Im either winding or unwinding wire then anyway.
I sure wish there was a 3b for 17, 15 and 10 meters!
Rick N8TGQ
N3NEI
Posts: 7
Joined: Mon Jun 27, 2022 7:14 am

Re: Linked End Fed Halfwave Antenna

Post by N3NEI »

A related question: As pointed out, an EFHW is resonant on multiple bands. For portable operations, where deployment conditions might vary, is it safe to trust the SWR will be as it should, or is some sort of SWR indicator recommended?
SkipRD
Posts: 60
Joined: Fri May 27, 2022 12:58 pm

Re: Linked End Fed Halfwave Antenna

Post by SkipRD »

N3NEI wrote: Fri Oct 14, 2022 5:06 am A related question: As pointed out, an EFHW is resonant on multiple bands. For portable operations, where deployment conditions might vary, is it safe to trust the SWR will be as it should, or is some sort of SWR indicator recommended?
My SW-3B doesn't have an SWR meter and I had the same concern, so I checked it just to be safe. The SWR was well below 2.0 on both 40 and 20, which were the only bands I care about, but just for the fun of it I checked it on 10 and 15 as well. If I recall correctly, it was at (or maybe slightly above) 2.0 on portions of one or both of those bands. I think that's to be expected. While an EFHW is "resonant" on all four bands, and one reads of antennas that are below 2.0 on all four bands, an EFHW may be slightly off on one end or the other depending on how it's cut. So, back to your question, I'd check and be prepared to do some adjustments just to be sure.

73 Skip K4EAK
N8TGQ
Posts: 78
Joined: Tue Jun 21, 2022 5:06 am

Re: Linked End Fed Halfwave Antenna

Post by N8TGQ »

I use the SOTA Tuner from QRP Guys. It has an SWR indicator built in. It also has a variable capacitor to fine-tune the antenna for different bands.
Rick N8TGQ
KN3A
Posts: 29
Joined: Mon Jun 06, 2022 11:42 am

Re: Linked End Fed Halfwave Antenna

Post by KN3A »

SkipRD wrote: Wed Oct 12, 2022 9:42 am I also have a linked EFHW, although I'm basically a slacker and went for the minimalist version, mostly because my Venus SW-3B only has three bands (20-30-40m). So, I have a 40m (66') EFHW, with one link at 49' 3" for 30m. That gives me all I need for now, and even with that I rarely pull the link and get on 30m. In fact, when operating solo I've always gotten to the end of my operating window on just 40 and 20 without going to 30. I've only pulled the link and used 30 once when there was another station with me and it was on 20. Even still, having 30m is a nice option in case there's a contest or something and I need a WARC band to find some clear air.

When I get (if ever) my KX2, I may add another link or two, or just go with a random wire and use the tuner.

So, to respond to your question (does a linked EFHW really help all that much?), I guess the answer for me is, maybe. Sometimes. A little. :D

73 Skip K4EAK
Skip - I like your idea for the link at 49'3"! When I SOTA and POTA, 20, 30 and 40 are my bands as well. I also have the SW-3C (wish I would have got the B). To me it makes more sense to just have the one link to get 30 meters as it will serve my needs when I'm out activating.

I may not have made myself clear, I do use a EFHW and was asking about the purpose of the linked EFHW. I got my answer and a great idea for my needs. I use a spark plug EFHW and at 66 ft. I get from 10-40 and with the link for 30, I'm in business. I do not like taking ATU's into the field with me, so I like the resonant antennas for deploying. 72 de KN3A
KN3A
Posts: 29
Joined: Mon Jun 06, 2022 11:42 am

Re: Linked End Fed Halfwave Antenna

Post by KN3A »

Skip - I did the EFHW link at 30 meters today. Maybe it's the balun (I'm using the spark plug) and I started at 50 ft 0 in. I ended up cutting 5 ft. 10 in. off of it! The total length is about 62 feet, so quite a difference from your measurements. Thanks for the idea, now I have 20-30-40 at near 1:1 SWR, which will be perfect for my QRP radios and no need for a tuner.

72 Scott
KN3A
SkipRD
Posts: 60
Joined: Fri May 27, 2022 12:58 pm

Re: Linked End Fed Halfwave Antenna

Post by SkipRD »

Scott ... I finally had a chance to unwind my linked EFHW and take some measurements. Here's what I found:

The 30m segment is 43' 10" long. Connecting the 40/20/15/10m segment makes the total length 63' 9". Of course everyone's dimensions will be slightly different, so YMMV. We're both in the same ballpark ... probably just differences in wire.

Testing the antenna gave me this:
40m: SWR < 1.5 across the entire band, with 1.24 and 1.14 at the CW portion edges.
30m: SWR < 1.2 across the entire band.
20m: SWR < 1.2 across the entire band, with 1.2 and 1.07 at the CW portion edges.
15m: SWR < 1.52 across the entire band, with 1.52 and 1.31 at the CW portion edges.
10m: SWR < 2.0 across the entire band, with 1.87 and 1.63 at the CW portion edges.
In other words, it's fine. 10m is maybe a little high, but the antenna is way good on 40, 30, and 20, which are the only bands my little SW-3B can use.

73 Skip K4EAK
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