03-08-2012, 02:01 PM
Lawrence,
The preferred method of underground (Radio) Communications is 'Leaky Feader', eg http://www.gai-tronics.org.uk/products/rfm.htm.
I assume you're not a 'Gassy Mine' so you don't care about Intrinsic Safety etc.
The original Systems worked on the old (low) PMR Band - 60-80MHz?
The one above, which is getting a bit out of date now, works on the VHF PMR Band.
Modern Systems are UHF and are designed to carry Voice, Video, Ethernet, etc, etc.
Now for the bad news:-
The systems use a special co-ax cable which is designed to leak rf, which is why you have to insert a Repeater every 500m or so. As the cable is a 'Linear Bilateral Network', you hope, you can receive from it and transmit into it.
For I.S. reasons the power levels are low - typically 1mW at the drive end of the cable.
Designing a two way Repeater - the go and return channels are typically 10MHz apart - with power splitting, while maintaining a decent match and linearity in both directions, is interesting.
You do, of course, need hand-helds at the right frequency.
Through-the-ground Systems have been about for years, but to my knowledge no-one has ever really made them work consistently. They usually kept for Emergency situations when you haven't got much choice.
Alan
The preferred method of underground (Radio) Communications is 'Leaky Feader', eg http://www.gai-tronics.org.uk/products/rfm.htm.
I assume you're not a 'Gassy Mine' so you don't care about Intrinsic Safety etc.
The original Systems worked on the old (low) PMR Band - 60-80MHz?
The one above, which is getting a bit out of date now, works on the VHF PMR Band.
Modern Systems are UHF and are designed to carry Voice, Video, Ethernet, etc, etc.
Now for the bad news:-
The systems use a special co-ax cable which is designed to leak rf, which is why you have to insert a Repeater every 500m or so. As the cable is a 'Linear Bilateral Network', you hope, you can receive from it and transmit into it.
For I.S. reasons the power levels are low - typically 1mW at the drive end of the cable.
Designing a two way Repeater - the go and return channels are typically 10MHz apart - with power splitting, while maintaining a decent match and linearity in both directions, is interesting.
You do, of course, need hand-helds at the right frequency.
Through-the-ground Systems have been about for years, but to my knowledge no-one has ever really made them work consistently. They usually kept for Emergency situations when you haven't got much choice.
Alan
