Skycop, it would be nice not to be quoted out of context - I was clearly referring to VMC flying.
You say we need a system to prevent IMC collisions. The only system which would prevent collisions is no IMC flying. Everything else is risk reduction. Transponders don't always work, radar services are not infallible and not always available.
We seem to have moved from compulsory transponders, at the beginning of this thread, to use of radio at this end. As radio is compulsory for gliders flying in cloud, though not, I think for powered aircraft (is that correct anyone?), but non-radio power is unlikely to fly IMC, this seems a promising starting point.
It's already established that power pilots are not reassured by monitoring the gliding frequency (130.4). Glider pilots don't know which ATC unit to call, and some power pilots think it unlikely that picking one of the local units is much use.
The logical conclusion is a common frequency for all class G IMC flying, with position reporting in an agreed, consistent manner at minimum time intervals. This might be by distance/bearing from a substantial town marked on the 1/2 mil map, or by GPS coordinates, plus altitude in each case. Safetycom might be a good candidate for this.
It seems to me that this would place a fairly light burden on all IMC fliers, and require minimal regulatory changes.
Comments?