--- In [email protected], "skipp025" <[EMAIL PROTECTED]> wrote: > > > Several years ago I Modified a GE Mastr II mobile to be a 220 > > (35 watts) repeater and placed an Advanced Receiver Research > > peramp with a resistor, capacitor and diode added for lighten > > protection. > > You should indicate the parts are for DC power line protection. > Not for protecting the GasFet from glitch events that might cause > the device to fail. > > > http://homepage.mac.com/pseabolt/mods/220.htm > > In a few years I modified another GE Master II for an 800 MHz > > repeater case and used the same pre-amp. (60 watts) > > You used an 800 MHz ARR Preamplifeir in the same type of hardware > configuration?
Typo, I used a ge mastr ii 150 -174 MHz and a 800 MHz base case to hold the repeater. > > > A few months ago I did another modification and added and > > external 220 amp. the amp is 28 volts and does over 200 watts > > but I am running about 100 watts. > > I see you are using a surplus Uniden ARX-2125 amplifier... but I > don't see any mention of how you biased the amplifier after the > modification? Do you know what class of service the amplifier is > biased to operate? I removed the SSB bias, the amp I am using is not a ARX 2125 shown on the web page. the amp has the same 5 driver boards but uses open air coils in place of the silver bars pictured. I looks pretty good on the spectrum analyzer > > > I placed a new AR2 preamp on the repeater and after a week > > the sensitivity went from .05 mv to open the squelch to > > .7 mv. The GasFET in the preamp was gone. I replaced the preamp > > with the orginal preamp than had been working for about 10 and > > a couple of weeks later, it gone too. > > I would expect a failure to happen unless you're running some > serious protection/filtering in front of the preamplifier. You > might want to use uV for your micro-volt label... otherwise folks > will assume you mean milli-volt or mV. GasFets will handle only > so much unwanted energy before they go on vacation. The duplexer has 95 db isolation I can't remember the name but the duplexer but they are copper and bigger than wacom duplexer and I have a 10 diameter wacom band pass filter between the duplexer and the pre amp. > > > Can you guys think of anything that would cause two amps to go > > in this short of time? Is this just coincidence or could the > > extra power have something to do with the failures. > > You don't say what type of duplexer, preselector and filtering you > have in front of the receiver preamplifier, but it's probably not > near enough protection. You also need to address the rf amplifiers > bias point and rf output filtering concerns. > > Rising to the 100 watt plus output level might be only a 3 to 6 dB > increase for a lot of folks... but shear quantity increase of > possible problematic and/or gremlin RF related to the repeater > operation is much more. The no free lunch rule applies and you must > pay even more attention to the details versus operation at lower > power levels. > > Pull the modified Uniden Power Amplifier out of operation until you > have a handle on what is going on. Tell us what type of filtering > you have in front of the receiver and preamplifier. I will reduced the power and give the preamp I repaired another try.Thanks > > s. >
