Tom wrote:
I've Googled in vain for an online calculator, or program for
calculating troughline dimensions - does anyone know of one, please?
The maths makes my brain hurt!

AppCAD at www.agilent.com has that and much more.

--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek