The Shorten 20
The End Fed Half Wave (EFHW) antenna for 10 and 20 meters is about 32 feet long. I want to create a shorten version of this antenna which will allow me to deploy the antenna easier as well as have a smaller footprint when I’m in the field. First I will have to find the specifications for a shorten 20 EFHW antenna. I hope to find it with some Ham Radio Facebook groups. Second, I will have to build a prototype. Fortunately, I have built a 10-20-40 Shorten EFHW, which works adequately for my needs, but I don’t know how efficient it is. Lastly, I will need to use the antenna in the field instead at home. Testing in the field will give me less interference with home appliances.
First I want to thank Mr. Werner and the following the Facebook groups: Making Antennas for Amateur Radio and Real End Fed Half Wave Antennas. Mr. Werner used MMANA software to predict how a Shorten EFHW 20 would be built. I knew that the first part of the antenna would have to be at least 5 meters long for the 49:1 transformer to resonate on 10 meters, thus the name End Fed Half Wave antenna. What Mr. Werner provided me was the coil size, 15 µH and the “pigtail” size of 1 meter. The pigtail is the final wire after the coil. The combination of the coil and the pigtail will reduce the antenna size to about 10 feet. A significant reduction when deployed at the field.
Materials and Build
I used the sotabeams.com antenna wire (DEF 61-12 Pt 6) and a PVC pipe (Charlotte PVC Pipe) for the coil to create the antenna.
To determine 15µH for the coil it took some experimentation. I know that self-inductance (Henries) is proportional to how many turns there are on the wire. So I took different lengths of wire, wrapped it to the PVC and measured their inductance to check if the proportion was linear; it was for my small sample of 5 measurements. Based on my initial measurements and creating an equation with my five figures using a linear regression, I figured 32 turns for 15µH. It turn out that 33 turns was sufficient to create a 15.1 µH. Measuring the length of the coil, it was 4.2 cm. I learned when using the LCR meter, its best to have the leads short. I was having skewed values when the leads were long.
I used 206 inches for the lead wire, a bit longer than 5.1 meters. It’s a good idea to make the antenna longer than shorter so you can adjust. Also, you don’t know the velocity factor of the wire which affects the length and thus the wavelength of the wire. As for the pigtail, I used the same sotabeam wire and I used 47 inches about 1.2 meters – also longer than specification.
I put the antenna together and used a 49:1 transformer from QRPGuys – a Mini 80m-10m No Tune End Fed Half Wave Antenna. At home, I hung the antenna on a mast and made sure the antenna was slopped.
Adjusting the Antenna
To measure the SWR, I used the RigExpert stick. I’m able to connect the “stick” to the computer via a USB C cable and read the SWR graphs. When I first measured the SWR, 10 meters was perfect. I had no adjustment, thus I kept the wire at 5.23 meters long.
Next is 20 meters. For 20 meters to work, the coil and the pigtail had to work together. Unfortunately, when I measured the antenna, it landed on 12.75 MHz which is 23.5 meters – too long. In addition, the antenna had a measurement of 4.3 SWR – too high. I was aiming for less than 2 SWR, but less than three is acceptable.
Fortunately, I had made the pigtail longer for this situation. The pigtail at this point was 47 inches, 1.2 meters long – the model predicted 1 meter long. I started to fold the pigtail on to itself to shorten the wire, plus I placed an insulator so I can attached a paracord in the future. I measured it again – NO effect. Then I shorten it more, by folding more wire and again no effect. At this point I was puzzled.
Basic antenna theory states the shorter the antenna the higher the band. I’ve read somewhere that if you fold too much antenna wire, it starts to create havoc to the measurements. Following the math and advice of many posts from Facebook, I decided to cut the wire and not fold the wire so much. I folded one inch and then measured. That wasn’t enough, so I cut an inch and then folded an inch, and measured it again. Eventually, I found a pattern and was careful not to cut too much. At one point I passed 20 meters (see the graph below), I had folded the wire too much. Thus I made the wire longer. On the final adjustment, I had 29 inches of pigtail and about 1.5 inches folding itself.
To test my prototype, I went to Prado Regional Park. The EFHW transformer from QRPGuys is for low power radios (QRP radios), so I decided to take my IC-705. I was able to deploy the antenna to a tree. I only had about two hours to test. At first, I was very worried that nobody answered my CQs on 20 meters. But, a good samaritan did answer my CQ. He told me he was able to hear me well. He was calling me back from Upland, about 20 miles away. His signal report was a 5-9.
The day after I took the antenna to Peter F. Schabarum Regional Park in Rowland Heights. For two hours I was not successful in contacting anyone. I was trying to call a NET in northern Texas. He couldn’t distinguish me between the noise floor and my signal. Which is typical for a QRP radio for a number of reasons. I did have great reception and was listening to many stations.
My next thought was to take the antenna to higher ground. I went to Chino Hills State Park. Chino Hills State Park, is elevated at about 1000 feet were I was setting up. I hear many stations from South Carolina to Lima, Peru. After three hours of trying, I wasn’t able to contact everyone. Which is unfortunate.
A few things that came to mind when testing the antenna.
- The antenna does a great job in receiving signals, better than what I expected
- The Solar Flux Index wasn’t that great and it might have affected my results for contacts
- The SWR was accurate in the field compared to that when I was at home
- I’ll need to follow up how much gain I loose when I create a Shorten EFHW antenna
- Could there have been a human factors? It’s been reported several times that sometimes amateur ham radio operators don’t answer back for a variety of reasons. To the point where some have said the bands are dead! I partially believe that, but there are good samaritans like the operator who answered my CQ because he heard me call for a long time.
- Trying the antenna on digital modes would be interesting
I want to continue with my journey with this antenna. My ultimate goal is to create an antenna that is less than 30 feet long, not a dipole, easy to deploy, self-tuned, and can resonate at 40 meters – ONLY That ;).