I have a couple of 100-Watt, 406-420 MHz MICOR Mobile radios. I picked them up at Dayton a few years ago since they were very inexpensive, and hoped that I could use them as some link radios. I'd like to find out how to use just the low power sections of the 100-watt mobile PA deck, as they would be running a high duty cycle. For the distance I'd be covering, 25 -50 watts or even much less would be overkill. Trying to find 406-420 MHz range 25 or 45 watt PAs to swap out has so far been impossible, so I'm hoping someone has disabled the last few PA deck sections to run them at lower power, and still has some notes on how they did any matching, etc. Larry
-----Original Message----- From: Eric Lemmon <[EMAIL PROTECTED]> Sent: May 10, 2005 6:26 PM To: [email protected] Subject: Re: [Repeater-Builder] Micor mobile transmitter Bruce, Although you can disconnect half of the four final transistors and change the matching components appropriately to have a 50 watt PA, it's better to simply exchange the 100W amplifier board for a lower power board. I'm guessing that you could probably find someone to swap boards with, maybe even make a few bucks in the deal.. It is not a good idea to reduce either the drive level or the PA supply voltage to achieve a lower power output, because the PA can become unstable. A solid-state PA is normally designed to present a stable source impedance which, in basic terms, is directly proportional to supply voltage and inversely proportional to PA current. Reducing the drive level will reduce PA current, thus raising the apparent PA source impedance and causing a mismatch with the load impedance- usually the reactive input impedance of a duplexer. This is not good, and is an invitation to instability. Reducing the supply voltage has the opposite effect on the apparent PA source impedance. If you have the requisite test equipment and time, you may be able to adjust both the drive level and the PA supply voltage to achieve stability at a lower power output level. This is a lot of work, and may be much more work than simply replacing the PA board. 73, Eric Lemmon WB6FLY brucenanney wrote: > What is the best way to reduce power on a 100 watt micor mobile for > repeater use? I have reduced the voltage in to 12.8 volts and have > developed a cooling system on the P.A. deck that has constant air flow > over the circuit board as well as the the heatsink. > Thanks, Bruce KD4BOH. > > > Yahoo! Groups Links > > > > Yahoo! Groups Links 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: http://docs.yahoo.com/info/terms/
