Additional construction notes:-
Constructed from 22mm (boom) and 15mm copper water pipe with Tee adaptor.
Plastic conduit inserted in 22mm tube to prevent wall collapsing.
Small drain hole in end cap at bottom of lower vertical leg.
Drill a hole (7-8mm ?) in the middle of the Tee for the coax to pass through.
When coax is pulled through hole, strip back braid for > 300mm and cut braid away about 10mm from coax outer sleeve.
Insulate coax outer with heat shrink to prevent melting when heated.
Insulate inner near braid with PTFE sleeving or heat shrink
Push sleeving back as far as you can under the braid to prevent melting when heated.
Fan out braid, pull back coax along boom and place braid over hole in Tee.
Solder braid to Tee with blowtorch and quench quickly to prevent coax melting.
Add Ferrite sleeve common mode choke on outer of coax inside the boom. Three cores from a PC monitor VGA cable or similar is good.
Set the elbow to elbow (a the base of the vertical sections) spacing at about 25mm so that you have room to adjust it either way.
Wrap two turns of 1.5mm mains cable around 15mm copper tube to form a tap for the gamma match connection, but don't solder it yet.
Connect inner of coax to gamma match tap and adjust position of tap and length of gamma match for best SWR (ideally 50 + J0 ).
Once best tap position has been found (with antenna raised above ground), disconnect inner of coax, and slip on short length of heat shrink.
Solder 1.5mm wire then reconnect inner coax and solder, strengthen solder joint with heat shrink.