--- In [email protected], Kevin Custer <[EMAIL PROTECTED]> wrote:
> 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. Kevin: I agree with your comments regarding component quality & its importance for stability. Having said that, my experience with the G.E. radios is quite different from yours. I've had MVPs at sites that experience 100 degree temperature swings for over 10 years & have seen no change in tuning of the trimcaps over that time frame. In fact, I don't recall ever seeing an unexplained change in trimcap tuning position on any G.E. radio. I have on occasion had trimcaps that froze in place & broke when I attempted to adjust them for the first time. I suspect they hadn't been adjusted in over 20 years. Coincidently, a friend of mine has an older UHF Mastr II RX (the one with tunable coils in the LO chain) in service that somehow got out of tune several months ago. My guess is that the tuning core wiggled out of place over a 10 year period. It's quite possible that some of the amateur grade repeaters out there were designed well. But if cheap, poor quality components are used they just won't be reliable. That could also explain why the manufacturers of these units often staunchly defend their product in the face of massive complaints. Bob NO6B Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
