It was my friend Eric ONBEW who drew my attention to a number of articles (from G3TXQ, DJ0IP and W7EL), which mentioned that a 1/4 Guanella balun must indeed be constructed on 2 separate cores.
In a single core, the balun does not seem to do its job properly.
Time to get to work and do some measurements.
Procedure:
I took a 2 core version as a reference and provided a connection by way of a clamp that was movable between the top of the output, the center and the bottom.
Schematic:
Results:
Overview Wurth dual core with the clamp not yet connected:
Overview LOT single core with the clamp not yet connected:
Overview FT140-43 single core with the clamp not yet connected:
Result: All seem to have a good result.
Next step is to connect the clamp to the top of the output. This will show the insulation between in and out.
Overview Wurth dual core with the clamp connected to the top of the output:
Overview LOT single core with the clamp connected to the top of the output:
Overview FT140-43 single core with the clamp connected to the top of the output:
Result: In all cases, we see a bit worse Return Loss at the low frequencies.
Next step is to connect the clamp to the center of the output. This will show the insulation between in and out.
Overview Wurth dual core with the clamp connected to the center of the output:
Overview LOT single core with the clamp connected to the center of the output:
Overview FT140-43 single core with the clamp connected to the center of the output:
Result: In all cases, we see a bit worse Return Loss at the low frequencies but the dual core is better.
Next step is to connect the clamp to the bottom of the output. This will show the insulation between in and out.
Overview Wurth dual core with the clamp connected to the bottom of the output:
Overview LOT single core with the clamp connected to the bottom of the output:
Overview FT140-43 single core with the clamp connected to the bottom of the output:
Dual core performs much better than the single core in all cases. Single core for a 1/4 guanella balun is actually not to be used!!!!!
Detail measuring results:
SWR Wurth dual core with the clamp not yet connected:
SWR LOT single core with the clamp not yet connected:
SWR FT140-43 single core with the clamp not yet connected:
RL Wurth dual core with the clamp connected to the top of the output:
RL LOT single core with the clamp connected to the top of the output:
RL FT140-43 single core with the clamp connected to the top of the output:
RL Wurth dual core with the clamp connected to the center of the output:
RL LOT single core with the clamp connected to the center of the output:
RL FT140-43 single core with the clamp connected to the center of the output:
RL Wurth dual core with the clamp connected to the bottom of the output:
RL LOT single core with the clamp connected to the bottom of the output:
RL FT140-43 single core with the clamp connected to the bottom of the output:
SWR Wurth dual core with the clamp connected to the bottom of the output:
SWR LOT single core with the clamp connected to the bottom of the output:
SWR FT140-43 single core with the clamp connected to the bottom of the output:
