mch wrote: >I think much of the problem is in the tuning caps on both the exciter and PA. > >Joe M. > >ac0y5 wrote: > > >>It seems a lot of the complaints are from oscillator drift and tuning drift. >>I have a few questions Does anyone know if the main problem resides in the >>exciter, or the power amp? >>
It has been my experience that any exciter or receiver that uses variable capacitors for the tuning elements has a poorer tuning stability. The Spectrum equipment seems worse than any other, and the problem *may* stem from the quality of the original parts used. Motorola identified this stability 'problem' many years ago and decided to use variable inductors where they could. My Micor repeaters have stayed in a perfect state of tuning since installed, for many, this is getting to be 15+ years. The biggest reason manufacturers use capacitors for tuning rather than inductors is it allows for greater operating (tuning) range with no change in parts. In other words they can tune a greater span of Mhz with the same part values. This 'feature' is nice because some commercial radios will more easily tune the ham band and retain original specifications, but at the expense of tuning stability. The GE Mastr II is a great radio, and is very popular because it tunes most of the ham bands without much, if any, modification, but they certainly don't have the stability of radio sets that utilize inductor tuning elements. All of the Mastr II's I have, have required retuning during the same time frame as above, (usually one a year for optimal performance) but they too use variable caps for the tuning. It only stands to reason that something that is limited to certain tuning 'ranges' will provide better stability. Inductor tuning doesn't lend itself to being pulled too far, so making one of these radios that were originally configured for the commercial band tune the ham band is more difficult because part change-out is a necessity, but you certainly don't have to worry about the thing going out of tune. Spectrum purposely designed their equipment to tune from DC to light, and while you can make them work very well, just don't expect them to stay..... Oh, to answer the rest of your question, in my opinion, every part of the Spectrum Radio is unstable, whether it be the receiver, exciter or PA. Kevin Custer Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
