ldgelectronics wrote: >Hello All, > >I have a requirement to install a battery backup system at a local >ham repeater. It's a GE Mastr II running about 100 watts. With that >much RF power, a couple of 100 AH batteries is only going to last a >few hours. > >My first thought was to add a second lower power RF amp (something >like 20 watts or so) and use coax switches tied to the AC mains to >switch to the smaller amp when the AC power was out. This should give >me a factor of 4 or 5 more amount of time on the backup batteries. > >The second thought (and here is where I need input), was to bring the >variable resistor (R8 on the VHF version) from the 10 watt driver >board to a smaller external board. Then add a second variable >resistor and a relay to switch between the two. This should give me >two independent amp settings that can be controlled by a single >control. > >Is there any reason why this should not work? It would save the cost >of the second smaller amp and two fairly expensive coaxial relays. > >The relay could be controlled from the repeater controller or >automatically with just a 12v DC wall wart. > >Dwayne Kincaid >WD8OYG > >
Dwayne, A (hopefully) better method would be to use two RF relays to switch in or out the final stage of the stock amplifier. This will allow the sections to operate with their normal / nominal power settings and give a larger current reduction when in battery mode. relay 1 common to driver output relay 1 normally closed to final input relay 1 normally open to relay 2 normally open relay 2 normally closed to final output relay 2 common to antenna filter assembly This assumes the relays would be energized when in battery mode. A little more drain on the battery, but 99% of the time the coils would not need to be energized. Ed Yoho WA6RQD
