The QRP Feather
I had previously built a QRP EFHW but I decided to rebuild it with a dedicated radiator. I tried to copy the design philosophy from the Chameleon CHA LEFS FEATHER EFHW.
The Build
I reused two of the Type 43 cores (Size: .827” (21mm) OD. Core: 5943000601). I wrapped it in a 3:21 autotransformer configuration for a 49:1 ratio with 16awg enamel wire. For these smaller cores, it is advisable to use 3 primary turns. This double stack config should be around 87% efficient. I put the cores on a 3D printed ‘sled’ with a BNC connector along with a 100pF capacitor. I used ~65’ of 26awg BNTECHGO silicone wire which I directly soldered on (after tying a knot for strain relief). I also used a 2m piece of wire as dedicated counterpoise soldered to the ground tab of the BNC connector.
Tuning
I deployed it as a sloper per Chameleon’s diagram above. Top of the wire was around 20’ up on the DX Commander mast. I put it on an electric fence stake and fed it with 25’ of RG-316 coax with a choke at the feed point.
For the tuning process, I got a slice of PEX pipe and drilled it to accommodate the antenna wire. This made it easy to trim the antenna wire to resonance and support the high end. This is a super lightweight end insulator.
Results were looking pretty good but I noticed that the harmonics were starting to creep a bit. I got it pretty much OK for 40m (though it’s still a bit long) and utilized a compensation coil to bring the upper bands back into resonance. The coil is installed about 6’ from the transformer. For more info on the coil, check out this video from Dude Tested.
Testing
Here are some nano sweeps for the bands:
10M
15M
20M
40M
It’s not too shabby. A bit high on the 40m band, but in my experience, it’s always a bit schmutzy on 40m when it’s deployed this low with a 49:1. I figured that I could always use my little manual tuner to touch up 40m if need be.
Conclusion
This is a nifty little build. I keep it in my QRP kit along with my WarcWiz and my 20m QRP dipole. With these three antennas, I’ve got the 40m-10m bases covered for all my QRP needs.
73 de VE5REV