[EMAIL PROTECTED] wrote:
Bob, First of all, please give Virgil a BIG thanks for his continued efforts on the subject. He obviously has taken a great deal of time and effort in building circuit simulation and practical circuitry to help explain this subject. My notes here aren't to serve to stir things up, but rather give input from real world observations from employing both PM and FM modulation methods (in their stock and modified form) within GE Mastr II, Hamtronics, and Motorola Micor radio sets utilized as voice repeaters. In the CTCSS and PM Paper, Virgil explains and shows that distortion results in PM systems passing CTCSS and Voice to a single stage LC modulator, like those found in radio equipment we commonly convert to repeaters. One thing that isn't discussed, however, is the distortion that will result when a (common) PM modulator is ask to follow the waveform, recovered from the discriminator, that was originally generated by a modern FM rig; again common to ham or commercial repeater operation. It is my belief that when the transmitted waveform of a FM user rig is analyzed, it will show that its demodulated waveform produces a modulating signal that a common PM modulator cannot follow. The area if particular interest is obviously in the lower frequencies. In addition, a good number of Japanese ham radios come off the shelf with nearly 1000 cycles of CTCSS deviation. This, combined with the already greater energy levels of the lower frequency voice signals makes it very difficult to impossible for the common PM modulator to keep. The result is distortion which can be heard. Again, this takes the equation one step deeper since we are talking about repeaters here. Of course, the easiest solution is to do what Virgil has shown; utilize FM in partial or whole for the transmitter expected to deal with all of this. Since the inception of this discussion some time ago much information has been passed and many have been shown the differences (and similarities) between these two modulation schemes. It has also shown that people listen and as they become more educated, expect better quality even from the simple ham repeater. These discussions have proven that people want a choice, even to the degree for companies like Repeater-Builder to offer True FM for the repeater transmitter, and better audio processing in which solutions like our Clipper/Filter Audio Processor Module resulted. Speaking of the RB Clipper/Filter, (shameless plug), it has been totally revamped packaging wise (all surface mount). If folks are interested in the particulars, I will address this in another mailing, just ask. Thanks again, Bob. Kevin Custer Yahoo! Groups Links
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