I recently tried to explain to a friend my perspective on the eternal "ham's" quest to find an all-purpose antenna as similar to someone searching for Bigfoot.... A futile endeavor but the search goes on. Every antenna is a compromise of function, efficiency, size and cost. Fairly recently I discovered End Fed Half-Wave (EFHW) antennas; or rather the transformers that do the magic of making a compact, multi-band radiator.
EFHWs are not to be confused with a 9:1 transformer feeding a wire at its "end." I have used an EARC 9:1 for several years and on many SOTA activations. They work but I definitely felt like I was compromising on efficiency. First and foremost, true EFHW antennas use a half-wave length of wire to make for a more efficient radiator. I stumbled across these antennas one day while on Facebook I saw a post about the End Fed Have Wave Antennas page. Once I joined the group I felt my eyes opened to new possibilities. Could this be my Yeti? Maybe.
Basically, a wire fed at the end presents an impedance between 2,700 and 3,000 Ohms. To match the impedance a typical radio requires (50 Ohms) you need a way to transform or match the impedance. Typically a 49:1 or 64:1 transformer will put you in the operating range sweet spot needed when you use the appropriate length of antenna wire.
My new discovery convinced me to buy a MyAntennas 80-10 EFHW. It uses a 49:1 transformer for operation on those primary amateur bands. Reluctantly, I had to cut the supplied antenna wire in half due to limited space in my backyard. Set up as an inverted-L it works great with <1.5:1 on the primary bands and I can use the internal tuning unit in my KX3 to make 30 and 17 meters work. I will write another post later about my homebrew 80-10 EFHW as it was another fun project.
Back to the point of this post. I am continually looking to lighten my backpack for my SOTA adventures so I thought I would give the QRPGuys "Portable No Tune End Fed Half Wave Antenna" kit a try. I have purchased a few kits from them before and found them to be fun as I enjoy building things and soldering.
This kit is an easy build if you have even modest soldering skills. It also offers the compactness I was looking for as the circuit board the components attach double as a wire winder. The longest part in the build for me was winding the toroid and making sure I had the number of winds correct. Once constructed I wasted no time in cutting some 22-gauge wire I had laying around to work on 40 meters; cut longer than prescribed in the instructions to account for any local variables.
Set up in my typical inverted-L configuration in the backyard, I initially just hooked the antenna up to my radio. To my relief I could hear a very active band. The magic of radio... When I connected my antenna analyzer I found the antenna was long for 40 meters, which I suspected as I cut it long. The dip on the meter was around 6.75 MHz. However, the SWR on 20 and 15 meters was good at <1.7:1. Not a good sign for a multi-band antenna.
I decided to make a cut to the wire length. I removed approximately 4 feet and re-tested. I was happy to see a SWR of 1.37:1 on 40 meters. Naturally, 20 and 15 were no longer in tune. I gave up for the evening as the the sun was setting and the mosquitoes were making their debut. The next morning I revisited the QRPGuys website and stumbled across an important note in the product description, "...using band specific radiator lengths." I should have seen this before. The thought of carrying different spools of wire length up a mountain to work different bands is impractical and a recipe for a tangled wire mess. I contemplated on just taking the one length of wire on my next activation but the prepper's mantra of, "two is one, one is none" quickly dissuaded me.
I definitely consider this kit field expedient for its compact size. For only $20 (US) it is an inexpensive kit to build and tinker with. Just keep in mind that QRPGuys specialize in...you guessed it, QRP or low power. This unit is limited to 10 Watts but it works. I will keep this around and may dedicate it for use in the shack as either a 30 or 60 meter antenna. I do plan to pack this on my next hike just to try it out, and to give me a second antenna option on a summit. After all, two is one and one is none.
Until next time, 73 and happy tinkering.
KH7AL
EFHWs are not to be confused with a 9:1 transformer feeding a wire at its "end." I have used an EARC 9:1 for several years and on many SOTA activations. They work but I definitely felt like I was compromising on efficiency. First and foremost, true EFHW antennas use a half-wave length of wire to make for a more efficient radiator. I stumbled across these antennas one day while on Facebook I saw a post about the End Fed Have Wave Antennas page. Once I joined the group I felt my eyes opened to new possibilities. Could this be my Yeti? Maybe.
Basically, a wire fed at the end presents an impedance between 2,700 and 3,000 Ohms. To match the impedance a typical radio requires (50 Ohms) you need a way to transform or match the impedance. Typically a 49:1 or 64:1 transformer will put you in the operating range sweet spot needed when you use the appropriate length of antenna wire.
My new discovery convinced me to buy a MyAntennas 80-10 EFHW. It uses a 49:1 transformer for operation on those primary amateur bands. Reluctantly, I had to cut the supplied antenna wire in half due to limited space in my backyard. Set up as an inverted-L it works great with <1.5:1 on the primary bands and I can use the internal tuning unit in my KX3 to make 30 and 17 meters work. I will write another post later about my homebrew 80-10 EFHW as it was another fun project.
Back to the point of this post. I am continually looking to lighten my backpack for my SOTA adventures so I thought I would give the QRPGuys "Portable No Tune End Fed Half Wave Antenna" kit a try. I have purchased a few kits from them before and found them to be fun as I enjoy building things and soldering.
The Build
 |
Removing insulation from the toroid wire.
|
This kit is an easy build if you have even modest soldering skills. It also offers the compactness I was looking for as the circuit board the components attach double as a wire winder. The longest part in the build for me was winding the toroid and making sure I had the number of winds correct. Once constructed I wasted no time in cutting some 22-gauge wire I had laying around to work on 40 meters; cut longer than prescribed in the instructions to account for any local variables.
Set up in my typical inverted-L configuration in the backyard, I initially just hooked the antenna up to my radio. To my relief I could hear a very active band. The magic of radio... When I connected my antenna analyzer I found the antenna was long for 40 meters, which I suspected as I cut it long. The dip on the meter was around 6.75 MHz. However, the SWR on 20 and 15 meters was good at <1.7:1. Not a good sign for a multi-band antenna.I decided to make a cut to the wire length. I removed approximately 4 feet and re-tested. I was happy to see a SWR of 1.37:1 on 40 meters. Naturally, 20 and 15 were no longer in tune. I gave up for the evening as the the sun was setting and the mosquitoes were making their debut. The next morning I revisited the QRPGuys website and stumbled across an important note in the product description, "...using band specific radiator lengths." I should have seen this before. The thought of carrying different spools of wire length up a mountain to work different bands is impractical and a recipe for a tangled wire mess. I contemplated on just taking the one length of wire on my next activation but the prepper's mantra of, "two is one, one is none" quickly dissuaded me.
Final Thoughts
I definitely consider this kit field expedient for its compact size. For only $20 (US) it is an inexpensive kit to build and tinker with. Just keep in mind that QRPGuys specialize in...you guessed it, QRP or low power. This unit is limited to 10 Watts but it works. I will keep this around and may dedicate it for use in the shack as either a 30 or 60 meter antenna. I do plan to pack this on my next hike just to try it out, and to give me a second antenna option on a summit. After all, two is one and one is none.
Until next time, 73 and happy tinkering.
KH7AL
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| Twisting the supplied wire for the primary winding. |
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| The antenna in my backyard as an Inverted-L. |
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