Impedance Bridging and Isolation Tranformer

This is not related to high quality audio (BTW).

In the world of audio engineering we typically see the load impedance about 10 or more times the source impedance. That's call high impedance bridging, voltage bridging or simply bridging.

Okay, I need to connect the low impedance output of my shortwave radio to line input of my soundcard via an isolating transformer. If the source output impedance is 35 Ohms and the line-in input impedance is 10K, what kind of transformer should I use?

Should it be 600 Ohms 1:1 transformer - or what? Is there a formula involved? Thanks.