KCØPET Pages
9:1 Unun
OK, many people might call this a "balun", but it is really not. A balun meanus a "balanced to unbalanced" transformer, typically to couple a coax feed line to a balanced antenna or feed line. This is really an "unun" or "unbalanced to unbalanced" transformer. (My daughter calls it an "onion", but it doesn't look or smell like one.)
Through various sources, I have read about using a 9:1 transformer for end fed wire antennas, but of course I have to try it before I pass judgement for myself! Also through EZNEC modeling, it would appear that a 450 ohm feed point helps control some of the wild impedences of an end fed wire antenna, particularly operating on multiple bands. The design is really simple. I used an FT114-43 core with 15 turns to 5 turns of #18 wire. I also added a "bypass" switch so I can compare the performance with and without the transformer. My intent is to use this with an autotuner.
My first try with this design was an 80' wire using the internal 20 watt autotuner in my K2. The antenna was configured as an inverted L. I also experimented with a 16' counerpoise wire. The antenna tuned up (about 1.1:1) and worked OK on 40 meters without the counterpoise. Set to "bypass" the antenna would not tune better than about 3:1 with the K2 autotuner. I found similar results on 30 meters, 20 meters, 17 meters and 15 meters. The counterpoise wire did not seem to make much difference on these bands in the ability to tune with the K2. My sense is, though that the counterpoise may make some difference in efficiency. This configuration (with counterpoise) also tuned up on 80 meters OK. But more experimenting is required...
Here is what the inside looks like:
