Yeah, makes sense. I was just thinking along the possible lines of the cap causing the drift... at least I could eliminate that issue, if it was an issue..
df --- In [email protected], "Eric Lemmon" <[EMAIL PROTECTED]> wrote: > > Dave, > > Keep in mind that the Midland 13-509 was built for the Amateur Radio market, > and the transmit crystals are only specified to maintain .001%, which is 10 > PPM. There is no temperature compensation in the crystal circuit, and you > may make the drift worse by using an NPO capacitor. If you have the time > and the test equipment to do it, you can determine a crude temperature > compensation by finding out how much the TX crystal drifts for a given > change in temperature, then using a capacitor whose TC has an equal but > opposite effect. This capacitor will definitely not be an NPO type, which > is stable over a wide temperature range. In fact, you want an "unstable" > capacitor that exactly balances the crystal drift. > > Commercial radios of the same vintage often used bare crystals with a color > dot on the side of the can, and you were instructed to install the > appropriate color TC capacitor with that particular crystal. Not perfect, > but adequate. > > You might also consider replacing the bare TX crystal oscillator with a > small TCXO unit from any of several sources, including ICM. > > 73, Eric Lemmon WB6FLY > > > -----Original Message----- > From: [email protected] > [mailto:[EMAIL PROTECTED] On Behalf Of na6df > Sent: Monday, May 22, 2006 10:48 AM > To: [email protected] > Subject: [Norton AntiSpam] [Repeater-Builder] midland 13-509 tx freq > stability... cap change? > > Working on my midland 220 box, with new international crystals. > Crystals are standard delivery, not "rushed", so they should be pretty > stable. They always are in my other rigs... > > Question: Is it worth swapping out the fixed value cap that is > paralleled across the ceramic trimmer on the transmit side? > Mine seems to drift around a bit more than I like. > > I have to assume the stock cap is an NPO type. Schematic does not > state capacitance of this cap. Anybody know what it is? RF Parts sells > NPO's, but is it worth it? Better ideas, if any? > > tnx and 73, > Dave NA6DF > > > > > > > > > > > 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/
