Hilary VK2AZ made a very interesting video on how to measure the return loss of the 10GHz dish antenna. He used the next calculator to calculate SWR http://cgi.www.telestrian.co.uk/cgi-bin/www.telestrian.co.uk/vswr.pl
More of VK2AZ videos you can find <here>
Photo: a screenshot of YouTube VK2AZ video
