At Why the preference for Guanella 1:1 current baluns for HF wire antennas I compared a 1:1 Guanella balun with a 4:1 using the same component baluns.
Broadly, the findings were that the common mode impedance of the 4:1 balun was around a quarter of that of the component baluns, and mediocre at that.
This article extends the reference, documenting the SPICE model extended to a 9:1 balun.
Above, the same component baluns were interconnected to make a 9:1 balun. Note that Zo of the TL section has been increased to 150Ω to suit the notional nominal 50 to 450Ω broadband transformer.
Above is a plot of Zcm from the model, and at 7MHz, Zcm is 260∠63°… quite low and quite inadequate as a common mode choke in an antenna system.
If Sevik's guidance was followed that Zcm of the component chokes was 50*500/3Ω, the common mode impedance would be even lower.
References / links
- Duffy, O. 2008. A model of a practical Guanella 1:1 balun. https://owenduffy.net/files/GuanellaBalun01.pdf.
- Sevik, J. Feb 2004. A Simplified Analysis of the Broadband Transmission Line Transformer In High Frequency Electronics Feb 2004.