--- On Tue, 11/1/11, Clutter <[email protected]> wrote:
> From: Clutter <[email protected]> > Subject: Re: [Drakelist] T-4XC Unstable PTO (I think) > To: "Paul Christensen" <[email protected]> > Date: Tuesday, November 1, 2011, 12:07 AM > Just to add my two cents worth- > > In my old, trusty Yaesu FT-101ZD, I had a similar annoying > 'chirpy' drift. In that case it turned out not to be a > frequency determining component at all. The 101ZD and > similar > radios had a bank of push button DPDT switches to select > fixed (crystal), external VFO, internal VFO, etc. The long > and > the short of it was that these switches in the signal path > > were somehow able to pull the oscillator and you could end > up > with a slightly different frequency if the switch contacts > were dirty. The usual fix applied, spray cleaner and > numerous > pushes of each switch to attempt to clean the contacts. > Dirty switch contacts sometimes produced an unstable, > warbly sort of audio beat note in the receiver, and > working the switch contacts definitely reduced it on the > spot- but only determined cleaning really stopped it from > happening. > > If there is any analogous switching on the R4/T4 that > might > even remotely be able to pull an oscillator > frequency, I'd > suggest that be looked at from the outset. A little spray > cleaner might save hours of needless hair pulling. > > I must say I was amazed at the time, to see how a switch > in > a signal path could pull an oscillator audibly like that. > > Alas, I figure it's far more likely it's some exotic NTC > cap in the oscillator circuit- or any sliding metal > contact > associated with the PTO. > > 73, David K3KY > > > > --- On Wed, 10/26/11, Paul Christensen <[email protected]> > wrote: > > > From: Paul Christensen <[email protected]> > > Subject: Re: [Drakelist] T-4XC Unstable PTO (I think) > > To: [email protected] > > Date: Wednesday, October 26, 2011, 12:43 PM > > > You would not be able to see a > > few tens of Hertz change on a scope. > > > > One method of observing small changes in frequency > (and > > phase) is to utilize the X-Y function on a scope to > display > > a Lissajous pattern. I have no doubt Garey has done > > this in the past. For others, one simply takes a > > known-stable RF generator and feed it into Channel 1 > of the > > scope. The PTO output is fed into Channel 2. The > > scope time base is set to "X-Y" mode. > > > > Next, the stable generator amplitude can be set to > > approximately equal that of the PTO. Amplitude > > equality does not have to be very precise. As > > frequency changes, so will phase. Two in phase and > > on-frequency signals will show on the scope's displays > as a > > straight 45 degree line. As the PTO changes > frequency, > > the line will turn into an oblong loop and continuing > > further, a perfect circle at 90 degrees of phase > difference, > > then it will show as a straight line again but at the > 135 > > and 315 degree points on the scope's display. > > > > With the Lissajous method, even the slightest change > in > > frequency between two sources can be displayed on a > scope. > > > > Paul, W9AC > > > > _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
