The graph now shows spot counts aggregated over various blocks of time rather than per two minute slot. The band colours match those used on the WSPRnet.org site.
My thanks to Mark, Phil and Ross for feedback and ideas. Phil, VK7JJ, has an exceptionally low noise level in Tasmania and he also runs an excellent web tool for plotting WSPR spot reception.
I've been picking up Peter, VK3YE, quite reliably and I asked him how he was doing the multi-band transmissions. He's been using a Zachtek WSPR transmitter which he reviews here:
Most entertainingly, Peter took the transmitter bus mobile and I was one of the stations that received him during a trip!
I like how peter holds the compact loop at the ground point of the feed line and how he notes the SWR change as the metal window frame changes the loop characteristics.