Hello Bob, >Kevin wrote: > > > 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. >
It wasn't my intention to place the GE line in the same category as Spectrum, rather to simply point out that inductor tuning has shown be be more stable over time than capacitor. To elaborate a bit more, quality radio manufacturers that utilize variable capacitor tuning use a good quality fixed value capacitor in association with the trimmer cap when larger capacitance is needed. This limits the 'range' of tuning and stability results. In the case of the Spectrum and other inferior brands, the values for inductance and the range of the variable capacitor allows for a very wide tuning range, but as agreed, at the expense of stability. If a circuit needs 50 pF of capacitance to resonate in the middle of the desired range, GE might have used a 40 pF fixed silvered mica and a 20 pF variable, where Spectrum simply used a 15 to 60 pF variable by itself. It has been my experience that GE Mastr II (and its variants) will 'properly' tune a wider frequency range than a Motorola Micor built in the same range, and is my reasoning that stability is then traded for tuning range. In other words, due to the 'mechanics' of tuning, the Mastr II is not going to be quite as stable as the Micor. Again, I'm not putting the Mastr II in the same category as Spectrum, but rather offering what I have found to be true. If you agree that the Mastr II will tune a wider range, then I believe you will have to agree with my theory. Kevin Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
