They ( in line rf amps) are commonly used in mines. They are bi-directional amps. Those I am familiar with split the vhf band in half... one half goes each way with filters to allow bi-directional duplex.. Mine Site Technology is one vendor.... The whole system operates under 5 watts... I guess that is a max power level according to some mine regulations, at least here in the US. The radio systems are duplex repeaters and work quite well.. Power for the amps is injected into the coax from one end but their are injectors and isolators installed periodically if the DC losses get too low..
On VHF the amps for one vendor are every 1500 feet or so...but it depends on gain and power and the size of the mine shaft.. Doug KD8B At 10:19 PM 2/18/2009, you wrote: >I don't think I've ever seen an amplifier along a leaky coax system. >Since the holes in the coax are 2-way, the downstream amp would also >amplify anything that leaked INTO the coax before it. That would >cause lots of interference as well as oscillation from the output of >the amp to the input. > >Now, if it was solid coax from the antenna to the in-line amp, I could >see that working. > >I think most systems today use fiber to get to the new RF source that >would then feed indoor antennas or leaky coax. So, one outside >antenna, RF to light on many fiber strands. In the tunnel, as one >leaky coax runs out of signal, another strand of fiber (or optical >directional coupler) would start another span of leaky coax. > >Again, I could be wrong about the re-amplification, just never seen a >system like that myself. > >Ray > >--- In ><mailto:Repeater-Builder%40yahoogroups.com>Repeater-Builder@yahoogroups.com, >"kabjik777" <kabjik...@...> >wrote: > > > > Dear all, > > I am a student currently researching on radiating leaky coaxial cables. > > I do understand that in long tunnels where radiating leaky coaxial > > cables are used, repeaters are placed at various points of the cable. > > > > I want to know what is the average distance between the repeaters. > > I will be glad if somone tell me or share a link with information as > > regards to this. > > > > I will also like to know the acceptable signal degradation per km? > > for example is it 15dB/km or 13dB/km? > > > > Thanks in advance. > > Bansoboy. > > > >
