Here is a new toy made with a FT 140-43 and 2 capacitors, total value = 139 pF.
Basically, it's a 28 turns auto transformer with a 3 turns tap
With a 3.3 kOhm between antenna and ground, I obtain the following curves
Return loss
- 19.85 dB @ 7.05 MHz, SWR = 1.22
-19.86 dB @ 10.1 MHz, SWR = 1.22
-18.84 dB @ 14.1 MHz, SWR = 1.26
-15.13 dB @ 21.1 MHz, SWR = 1.42
-11.6 dB @ 24.9 MHz, SWR = 1.71
-8.6 dB @ 28.5 MHz, SWR = 2.18
What about insertion loss ?
To evaluate IL, I made this test circuit
With 2 x FT 140-43, the IL is as follows
0,34 dB @ 7.05 MHz => for 5W input power, 4,62 W go to antenna
0,37 @ 10.1 MHz => 4,59 W to antenna
0.4 dB @ 14.1 MHz => 4,56 W to antenna
1 dB @ 28.5 MHz => 3.9 W to antenna
