[R-390] BFO Drift?

[ANTHONY CASORSO]

Thats the one I was referring to. He said that a 3 volt line variation produced a 6 Hz shift. I know this is true because, when my wife fires up her iron while I have a steady tone in the speaker, I can hear the tone bounce quite clearly.
 
Dallas just hacked in a 12 volt 3 terminal regulator and fed 12vdc to the BFO/PTO filament string through the 3TF7 socket. This made it immune to line fluctuations.
 
When you are using someting like ARGO or SPECTRAN to listen to weak beacons, any shift is clearly visible in the waterfall display.
 
Tony> Date: Thu, 11 Dec 2008 17:15:41 -0500> To: r-390 at mailman.qth.net> From: ews265 at rochester.rr.com> Subject: Re: [R-390] BFO Drift?> > Tony mentioned Dallas' "filament regulator" idea. If that's the > Dallas article I think it is, I recall that he showed that the 3TF7 > ballast wasn't really that effective at stabilizing heater current > and therefore oscillator stability. Don't remember the details but I > think he powered the PTO (and BFO?) filaments from a separate > external source and then wiggled the AC line input to the > receiver. I recall that this showed that the freq stability of the > receiver was considerably better than when the PTO - BFO - 3TF7 > string was allowed to wiggle along with the rest of the receiver.> > Bottom Line - Most of the freq instability due to line voltage > variation is due to the resultant current change in the PTO - BFO - > 3TF7 string. I THINK this is what I remember of Dallas' findings.> > Jon - WA3MVM> > > > At 03:43 PM 12/11/2008 -0600, Barry wrote:> >>You can take a look at the heater/filament voltages to see if you > >>can spot any variation over time. Another thought along the same > >>lines is to operate the BFO heater on a separate supply. This is a > >>complicated test though since I seem to recall that the BFO and PTO > >>heaters are in series along with the 3TF7. Try to isolate which > >>oscillator is doing the dance before getting into his kind of thing.> >>> >>Regards,> >>Jon WA3MVM> >> >Wouldn't it take considerable fluctuation in the AC supply to cause > >a significant shift in these oscillator frequencies? I ran one from > >the 12.6V supply from the power transformer and bypassed the 3TF7 > >altogether. I never noticed any drift, etc.> >> >Barry - N4BUQ> >_____________________________________________________________> >R-390 mailing list> >Home: http://mailman.qth.net/mailman/listinfo/r-390> >Help: http://mailman.qth.net/faq.htm> >Post: mailto:R-390 at mailman.qth.net> >Unsubscribe: http://mailman.qth.net/mailman/options/r-390> > > _____________________________________________________________> R-390 mailing list> Home: http://mailman.qth.net/mailman/listinfo/r-390> Help: http://mailman.qth.net/faq.htm> Post: mailto:R-390 at mailman.qth.net> Unsubscribe: http://mailman.qth.net/mailman/options/r-390
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