Theory
Windings
Why a 12 turn instead of a 9 turn? Because of inductance. 9:1 transformers designs are typically presented with T106 or larger transformers. Using the calculator at https://toroids.info I was able to determine that the amount of inductance for 9 turns around a T106-6 is 0.94uH. To approximate that amount of inductance with a T94-6 takes 12 turns to get 1.01uH. The transformer was markedly better with 12 turns versus 9.
Transformer Theory
I like the diagrams on M0UKD 9:1 page. The first shows the physical aspect of the trifilar wound transformer. The second shows the circuit that is being implemented.
Like the EFHW transformer, there is ratio of turns in the primary versus the secondary. In this case we have 3 times the primary in the secondary. Thus it is a 9:1 transformer.
This transformer steps down a 450 Ohm impedence to 50 Ohms.
Antenna Length
The random in end fed random wire antenna is a misnomer. In order for the antenna to work, you must avoid half-wave lengths.
| Antenna Length | CP | Usable bands |
|---|---|---|
| 34’1, 41’, 58' | 13’, 17' | 40-30-20-17-15-12-10 |
| 71’, 84’2 | 17’, 33' | 80-40-30-20-17-15-12-10 |
1 34’, 35’, and 35.5’ are commonly used lengths.
2 84’ antenna with a 17’ counterpoise is a W3EDP antenna.