Re: [Repeater-Builder] Repeater audio

[scomind]

Hi Kevin,   I could be wrong, but I believe all low band Micor exciters (including Stations) are PM.  This is likely the case because it is difficult to modulate the crystal frequency via direct FM, retain good linearity, and achieve 5 kc's of final deviation due to the multiplication factor.  Since the low band stuff is generally only multiplied a few times, rubbering the crystal via an FM modulator would require the crystal frequency to be swung 1/3 of 5 kc, or + and - 1667 cycles.  This isn't something I would think would be easy to do.   True, and that helped give PM a head start long ago. With PM, you modulate the stage after the crystal oscillator, and the crystal doesn't need elasticity like it does in FM.   BTW, the elasticity of a crystal is specified by its "motional capacitance". For many applications, the crystal manufacturer makes the motional capacitance as small as possible because crystal frequency movement is a bad thing. But for FM, we want a big motional capacitance, and the manufacturer has to be aware that the crystal will be used for FM.       Hamtronics mentions in their manual for the TA-51 (a little PM exciter they have built and sold for years) that a full 5 kc of deviation *may not* be possible without distortion because the multiplication factor is only 4 times with their 6 meter exciter.  (Read page 7 of the following manual): http://www.hamtronics.com/pdf/inst%20manuals/TA51.pdf   Since that exciter has a crystal oscillator stage followed by a phase modulator stage, Hamtronics could have designed it to have more deviation than it does. Maybe they decided to keep the design the same for all the exciters regardless of band.   73, Bob Yahoo! Groups Links To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/   To unsubscribe from this group, send an email to: [EMAIL PROTECTED]   Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.