Here's a photo of my 49:1 UNUN consisting of 2 FT240-43 stacked cores. I built it according to Steve Dick, K1RF's reference on EFHW antennas.

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Quote from: gil on June 08, 2021, 03:55:20 PMThat my friend is a very important statement...

I recently upgraded my K2 with the KPA100 internal amplifier. I built a new UNUN using two stacked FT240-43 cores. According to the reference from K1RF it can handle 300W PEP. I tuned into the Utah Web SDR (ca. 500 miles from my QTH) on 20m and keyed down for several seconds. I saw a very strong S9 + 60 dB signal, loud and clear. It was by far the strongest signal on the display. To make a long story short, I incrementally reduced the power down to 0.1 W. Even at 0.1 W, I still saw a nice clear S5 to S6 signal on the SDR. I could have worked any station in Utah that night with 0.1 W as long as the receiving station's noise floor was low enough.

Assuming that the band is open, there are only three reasons I found QRP doesn't quite get through. There may be more, but these are the ones I noticed:

1. The far field radiation pattern is not the ideal pattern and the station lies within a null. Unless your dipole or EFHW is horizontal and 1/2 wave length above the ground and free of obstructions, you have nulls.

2. Something is defective in your equipment and the antenna isn't radiating at all.

3. The receiving station has a very high noise floor, and your signal falls below it.

When does QRO power help? It helps only in two cases that I can discern:

1. Getting your signal above the noise floor, especially for stations fighting an S8 or S9 noise floor. This seems more common on SSB than CW.

2. Marginal band conditions. Having more power, your signal may only drop from an S9 to an S7, which is better than a QRP signal dropping from an S5 to an S3 and below the receiving stations noise floor.

Should we ditch our amplifiers and go QRP only? Outside of a prepping situation, probably not. The other thing I learned from my little SDR experiment is with each power reduction, I did see a signal strength reduction on the SDR. That tells me two stacked FT240-43 toroids can handle 100W CW without saturating. Otherwise, there would have been no change in the SDR reading until I got below the saturation threshold.

My EFHW can handle 300W PEP, but it's still a compromise antenna. It is too low to the ground and too close to buildings to have a predictable far field radiation pattern. I have no idea what the radiation pattern really is. I need to either get it up 10m in the sky, which isn't really feasible at my QTH, or construct an antenna that doesn't need to be mounted as high. I am considering a delta loop in this case. Further down the road, I would like to build a portable 2 el Yagi and mount it on a 10m military fiberglass push up mast. Probably not the ideal antenna for prepping, but would be a great antenna for field day, camping, or natural disasters and other emergency comms. My intent is to try to get away from using a compromise antenna so that the performance will be more predictable.

73, de Brian

Quote from: gil on June 01, 2021, 02:56:49 AM....Interestingly I just tested a 49:1 with an FT-240-61 core, two turns primary, and it did not work on Hf or 6m........ The same one using an FT-240-43 works great... What do you think of that?
Gil.

Gil -

The document I linked above, The End Fed Half Wave Antenna by Steve Dick, K1RF - page 26, common problems are, "Using wrong toroid materials. Stay away from type 61 ferrite cores and any powdered iron cores like -2 or -6. Primary inductance too low and it won't work." Which explains your result.

Page 24 of the same document, "More than 1 toroid generally improves efficiency: Single FT240-43, 2T/14T wind is 66.5% efficient on 80M and has inadequate primary inductance/high VSWR. For a 100W rig on CW, dissipates 14.7 watts – much too high." Which matches Asen, LZ2DMs, observation above.

Another resource I use is http://toroids.info.

73 de Brian KM6ZX

It looks like you are driving your -43 UNUN into saturation at 50W. According to the chart on Page 25 of: End Fed Half Waves - Steve Dick K1RF, a single -43 UNUN can take 15W continuous power. So I'm thinking your antenna is emitting about 15 W of RF energy, and 35 W is being transformed to heat. If you repeat the test with less than 15 W, your UNUN should be closer to 90% efficient. I am building an UNUN with two stacked FT240-43 cores that can, according to the linked PDF, take 85W continuous power. CW and SSB are not continuous duty cycles, so the max power rating would be 212W and 340W respectively.

Keep posting and let us know your results. I don't have the ability to conduct any measurements, so have to build my antennas based on references and expect they perform up to spec.

73 de Brian KM6ZX

Quote from: gil on May 27, 2021, 06:16:21 AM....Truth is, the impedance of a half-wave wire is very difficult to measure and theoretically should be infinite, but it isn't...

I was thinking about this statement. An end-fed antenna is an unbalanced antenna, because one end of the antenna connected to the shield of the coaxial cable through the UNUN, and the shield is grounded. The impedance cannot be infinite because there is an electrical path to ground.

I honestly don't believe the EFHW is the most efficient antenna for QRP operations, and trying to get 5% more out of it is kind of a science project without much real-world benefit. Personally, I like using a doublet with balanced feed line to a multi-Z tuner for QRP work. Maybe it's more efficient, or maybe it's the placebo effect, but I feel it works better most of the time. I posted on that antenna here earlier. After watching your videos, I think the next step to improve on the doublet would be the Delta Loop fed with balanced twin-lead line, especially on 10 m, where the size is small enough to be practical and the band is now starting to open up regularly.

Experimenting with antennas is part of the fun of QRP operations. Build lots of antennas, try things out, and see what works and doesn't. That's my favorite part of your YouTube channel. You aren't afraid to experiment and have given us lots of ideas.

You could just take 1 secondary turn off a 49:1 BALUN to get 42:1. I have tried both 49:1 and 64:1 BALUNS with my end-fed antennas and have not noticed much difference between the two. So I don't think there would be much practical difference between 49:1 or 42:1.

PS: The impedance of an antenna is dependent on its proximity to the ground and other objects. The theoretical impedance is for a horizontal dipole, 1/2 wave length above the ground. Since you measured with the antenna oriented vertically, it makes sense the impedance would be slightly different.

I'm not so sure about that, i.e. 75 ohms is better for power handling or 35 ohms is better for reception. I would think feed line loss at the desired frequency would be the most important factor. Maybe others can chime in here.

I do know that at HF frequencies, feed line loss isn't as much of a problem as it is at VHF frequencies. Also we operate in the field or portable, so feed line lengths are much shorter than fixed installations. That being said, QRP can use lossy feed lines and still work very well.

Imho, the most important factor to having good reception is a low noise floor. So I would want a feed line that doesn't act as an antenna and add to my noise floor. Also, a separate receive antenna could help in some high-noise environments.

The QRP-Labs QCX Mini is now available here: https://www.qrp-labs.com/qcxmini.html

I wasn't originally planning on getting one, since I already have two QCXs (80m and 40m). But it is such a cute, useful and inexpensive little radio, I wound up ordering one on 20m.

This radio is no longer vaporware!!! The Discovery TX-500 is now on sale at  Ham Radio Outlet. There is already a review up on .

You can't go wrong starting on 40m. Most slow speed CW is between 7.050 and 7.060 or above 7.110 MHz.

While browsing the NorCal QRP web site, I stumbled upon this very nice design for a portable doublet antenna: Norcal Doublet

Since I operate portable QRP, I am always looking for new antenna ideas, and up to now have never found a center-fed dipole that I was happy with. I ordered 65 feet of 4-strand ribbon cable for $9.99, made end insulators from an old paint mixing stick, and used a few odds and ends from my junk box. I made the elements each 22 feet in length, per the Norcal design, but left the remainder of the cable to be a feed line, so that I could lengthen the elements later on if I want to. I attached one end to a tree, and used two collapsable poles for the center and other end. The antenna was perfectly horizontal at 20 feet. Setup took only a few minutes.

I used a QRP-Guys Multi-Z tuner, which can take balanced line. I was able to tune the doublet on 40, 30 and 20 meters. Using my 5 watt, 40m QCX transceiver, I made an initial QSO with someone in San Diego, distance 246 miles. He reported my signal at 599. I made a second QSO into Utah, distance 310 miles, reporting 559. This was mid afternoon, so the band hadn't completely opened up yet.

I really like this antenna. It is it is very light, easy to setup, the feed line loss is minimal, and so far has given me very good results. I may lengthen the elements to 33 feet each, which is close to the recommended length for a 40m doublet. I will also make a 4:1 balun, so I can connect it directly to my K2's auto tuner.

For me personally, my ideal field setup would be a combination of a vertical, such as the QRP guys trio-band vertical, and this antenna. This antenna would also work very well in a stealth installation.

73,

Brian

"Who are these Experts?" Sorry... I was basing what I said off of a book I read, "The Art and Skill of Radio-Telegraphy" by William G. Pierpont N0HFF. I am obviously not a pro, so I can only go off of what I read and my own self training, and my very limited experience in CW.

I guess the point I was trying to make is head copy and paper copy are separate skills, and if you write everything down and never learn to head copy, it can become a handicap.

PS: I am interested in participating in CW traffic nets, even though it's completely obsolete and hardly anyone sends radiograms any more. But in a natural disaster, it could become a very useful skill. So I do care about being able to accurately copy messages, as opposed to just carrying on a conversation.

The experts say, throw away the pencil and learn to head copy. And that is a good skill to have. When I'm on the air, it's mostly head copy with a few notes. Writing down every letter can turn into a handicap. But OTOH, for passing messages, traffic nets, etc. you need to be able to copy morse code. So I have practiced both, because I want to be able to use morse code for more than just on-the-air QSOs.

Copying code takes a lot of practice. I occasionally copy the W1AW transmissions, especially the 18 WPM propagation report, because it contains a good mix of characters, symbols, and letters. And I recently received a certificate from the 20 WPM qualifying run. I hope to qualify at 25 and 30 WPM some day. The trick is to learn to copy from behind. That is you wait until you recognize the word before writing it down, and while writing, you're listening for the next word. It's not easy, but it's kind of fun.

I guess I'll chime in again. I used the Koch method at 15 WPM and 20 WPM character speed. I typed in my copy on a PC, so the computer could grade it instantly. I don't know if head copy is right or wrong, but typing my copy worked for me and I don't think it slowed my learning down. The purpose of the Koch method is to teach your mind to instantly recognize Morse code characters, and how can you know if you recognized the correct character unless you have some form of copy? Character recognition is the foundation for everything else, and eventually you'll start to recognize common words, and be able to head copy much of what's being sent on the air.

There's a difference between memorizing and learning. If you want to memorize the code, that video is fine. If you want to learn the code to communicate, I wouldn't recommend it. I personally learned by using the Koch method at 15 WPM. You start out listening to 2 letters, and add letters one at a time. This method worked for me and I am now at 25 WPM.