Interestingly enough, for most repeaters with average use, the idle (receive) current over time is a more significant draw than the briefer periods of transmit. An additional modification that you can use to lower the idle current, is to remove power from the audio amp (of course, this will only work if you are feeding your repeater from the discriminator and don't want a local speaker). There is a single resistor that powers the audio amp, so you just lift that resistor. I don't have the R number handy, so consult the schematic. If you have problems figuring out which one, let me know and I'll look it up for you. IIRC, it is one of the resistors that live on the right side of the audio board (with the radio oriented with the big main connector and the RF ports towards you, and the PA away from you) between the discriminator enclosure and the wall of the radio. This will also allow you to eliminate the power resistor used to load the audio amp. I've done this on all of my MASTR II repeaters with no problems. Keith McQueen 801-224-9460 [EMAIL PROTECTED]
-----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Ed Yoho Sent: Tuesday, October 16, 2007 7:37 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Reducing power out when on battery backup. 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
