I just happened upon an App. note written by Philips
Semiconductors (ECO6907) titled "Design of HF wideband power
transformers" which states for both 4:1 and 9:1 transmission
line transformers that they CAN be wound on a single core if
desired for certain conditions (see sections 6.3, 6.4 and 6.6).

http://www.semiconductors.philips.co...es/ECO6907.pdf

73,
Larry, W0QE