In reply to 2E0KPO:
When I started using the Diamond I had an old aluminium framed rucksack which just happened to be approximately one half wave tall on two metres and around about a quarter wave by just under a quarter wave at the base. This frame seemed to work as a pretty good ground plane and I had no problems with the swr. The antenna was mounted onto another piece of aluminium tube with an L bracket at the top which was fitted with a mobile mount.
I used this set up to successfully keep in touch with my XYL Helen GW7AAU back at home during a number of accents of local hills and it worked very well. It also did the trick when the WX was not too kind and I operated with the rucksack leaning against the trig point a few times.
However I did try mounting the antenna on the SOTA pole by tie wrapping the aluminium half wave pole to it but found that it worked a lot better on the rucksack. The half wave antenna (also a Diamond) that I currently use on the car worked much better on the SOTA pole with the mounting pole basically turning it into a dipole.
I have since replaced my rucksack with a modern internal framed one and have since found the 7900 doesn’t work as well any more (no Ground plane!) so I use the half wave instead (when there are no trees on the ascent). It is not as good but is better than the 7900 without ground planes. For simplicity I have made a roll up J-pole antenna which we Velcro to the SOTA pole beneath the HF antenna on the summits. I did consider that the J-pole could be used as a rucksack antenna on a partially extended SOTA pole.
I have been promising myself for three years that I will make a 2m SOTA beam but still haven’t got around to it. All credit to Richard G3CWI but I hate the idea of those crocodile clips and I am still trying to think of a better way that doesn’t involve a major engineering project or the use of screw drivers on the summits.
Whatever you do best of luck.
Regards Steve GW7AAV