I first heard this suggestion on an episode of Chef at Home with Chef Michael Smith. I can't remember his ratio of cardamom to coffee, but I like is 5-6 cardamom pods to 4-5 c of coffee. Really, how strong the flavour of cardamom becomes is a personal preference. Experiment!
5-6 Cardamom pods, crushed (I use a mortar and pestle)
Freshly Ground Coffee
Place the coffee, the crushed cardamom, and the boiled water together. Allow to "steep" to desired strenth. Enjoy!