We have been selling the Fair-Rite 2643101902 Mix 43 round core for some time as an ideal core for making 100W EFHW transformers, as well as good common-mode chokes. This core is included in our EFHW and CMC kit as an option.
This evening, we put the core to the test using a NanoVNA to measure the return loss of two PCBs back to back. The transformers were wound 49:1. The PCBs were soldered together by flipping one over and soldering the antenna and counterpoise tracks together, then connecting the SO239 point using a short length of RG316 to the VNA.
This is the setup. Apologies for the rambling; I did it pretty quickly.
There are two cores back-to-back 49:1 on our PCBs, which are then placed on a box and connected to a NanoVNA.
Connected up to a VNA.
I wanted to do this test because a lot of Radio Amateurs say that mounting a transformer on a PCB will result in big losses. I really don't think they have thought this comment through well considering the transceivers use PCBs with components on them.
Anyway, here are the results, with some very small adjustments for the cable loss.
This really is good: over 91% efficiency from 80m to 10m. I now just have to test it as an antenna in the wild. Watch this space.
It might be possible to get this a little more efficient with different windings or as an autotransformer. But for now, this is a pretty good result.
And here is the original VNA sweep with the cable loss.
Here is the test result from which the efficiency data is taken.
Anyway, great results. We will always look to improve our antennas; this core and PCB combo will give us a really good 100W option for the QTH.
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