Graeme,
I use Sylvain's CORONO
http://sweiller.free.fr/Softwares/Corono/corono.html
Easy and accurate to use - recommended.
Guys,
Thanks for the positive support, appreciated.
The CaK filter assembly I use is a DIY construction, it has the narrow bandwidth which should pull out the CaK line detail.
I've had "shadows" of proms before, but this one.... just made my day!!