Cactus V2s Modification
A few people have asked if I would mind showing the modification I made to my Gadget Infinity Cactus V2s, so here are the details of what I did. Please note that I will not be held responsible if you attempt to make this modification, and kill your triggers – anything you do is at your own risk! Also, an apology for the quality of the soldering in the shots…
Anyway, the main aim was to add an antenna to improve transmission. Not knowing much about this sort of thing, I consulted one of the electrical engineers at work, and he pointed out that for best results, the length of wire running between the antenna itself and the circuit board needs to be shielded, and it’s that element which is the main difference between this modification and others you may see around the ‘net.
Unfortunately I can’t find the original invoice for the parts I used, so a rough description will have to suffice, but you should be able to get the appropriate parts from any reasonable electronics supplier (Maplin, etc). The 4 bits you need are the antenna itself (which is very specific one sized for 1/4 the wavelength of the V2s overall transmission wavelength – apparently being a clean 
“slice” of the wavelength, other than just some random length, will give you a far cleaner signal); next is the mounting for the antenna – simply purchase the one which fits the antenna you are using; next is some shielded cable – this is effectively very thin co-ax, with a wire weave wrapping the main, signal carrying core; finally, a regular piece of thin wire (I used single core from an old network cable).
Your first job is to drill a hole in the lid of the transmitter just the right size to allow the antenna mount to be fitted. Next, cut a short piece of the shielded cable, and solder the shield (the mesh/weave) to the outer contact on the antenna mount, then solder the cable core to the core contact on the antenna mount. Essentially, using the shielded cable ensures that the antenna is the exact length you want it to be, and that the extra wire to link the antenna to the PCB doesn’t pick up any extra signal (at an uneven multiple of the wavelength, which would actually reduce signal quality). Next solder the core of the shielded cable to the PCB at the antenna point towards the top left of the PCB.
The final job is to take the remaining piece of wire, and solder that to the loose mesh end of the shielded cable (make sure the join you make here is not making contact with anything on the PCB, or alternatively, just put some insulation tape around it). Run the wire across the PCB however you like, so that the other end reaches the negative battery terminal, and solder to that. The idea here is that you are effectively (or as near as we have available) earthing the shielding around the cable running from the antenna to the PCB, so any spurious signal caught by the mesh gets dumped into the battery, leaving you with a nice clean signal!
So, there you go. I tried this modification first without the shielded cable, and the reliability and range seemed substantially less than with it, so the mod appears to do some good. If anyone would like to perform some more scientific test, please feel free to post your findings below!
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