I understand that if GRN voice failed at network level, it means the local tower is either operating by itself (not connected to the rest of the GRN network but replaying local voice traffic) or the local tower is out of action.
Either way, a field command vehicle with a local GRN repeater would resolve the issue for a long term commitment.
does such a thing exist? GRN sites use a microwave link to connect to the network/NOCC, it could be done on a something like a regional comms van but is it? I didn't think so, but could be wrong...
Two metropolitan SES Units have portable GRN repeaters which were mainly designed to beat the 'dead spots' in the GRN network. Baically two GRN radios on specific talkgroups that automatically repeat the voice traffic between themselves.
The SES Units have used them on cliff face rescue to ensure the GRN radios work when you are 'on the cliff face'. They anchor the GRN repeater at the top of the cliff face.
SES NSW have had specific trailers built that are GRN portable repeaters. These are self contained & can be delivered, setup & run anywhere. They contain two GRN radios, pump-up aerial mast and generator. Because NSW & SA are trunked systems, each tower can repeat the signal if required. So tower can talk to another tower until it find a better way (be it microwave or cable)
If you had a crew working in a valley which is a GRN deadspot (eg Onkaparinga George, Deep Creek, Flinders Ranges, Mylor, Adelaide Hills, etc) then the trailer is setup on high point where its pump-up aerial can communicate with a tower. The other aerial can provide communication into the valley.
SAAS also have local GRN repeaters in each of the ambulances.
Murray Bridge SES Field Command & CFS Region 1 Ops have pump-up aerial masts. So they can work has a repeater but just with a person between the radios rather than automatic.