The frequency stability of any transmitter is only as good as it's reference oscillator (be that a PLL or a multiplied crystal)- dividing or multiplying the frequency will not change that constant (in PPM). It doesn't matter if you use a 100KHz, 1MHz, 10MHz or 100MHz reference frequency, if they are all the same in PPM. You don't somehow get better stability by dividing the frequency, and you don't get worse by multiplying the frequency. It is what it is.
Joe --- Wade Lake <[EMAIL PROTECTED]> wrote: > Kevin, > > I now realize the mistake I was making in > looking at this. I am used to seeing newer PLL's > with a much higher reference oscillator frequency > and having a divider in the reference side before > the Phase Comparator. In that case the stability > does improve over that of the reference oscillator, > but that obviously does not apply here. > > Sorry, I will shut up now. > > Wade - KR7K > > ----- Original Message ----- > From: Kevin Custer > To: Repeater-Builder@yahoogroups.com > Sent: Sunday, December 19, 2004 4:16 PM > Subject: Re: [Repeater-Builder] GE Mastr II PLL vs. > Multiplier (crystal) exciter in duplex service. > > > Wade, > > If the PLL reference from the crystal is X3, and the > VCO sample has been divided by 4, what is the > product of 3 times 4? The answer is 12. If the > transmitter was any more stable in frequency than > the reference, shouldn't one think the stated > frequency stability would be better than 2 PPM or 5 > PPM, which is the stability of the ICOM itself? > Many times the manual states the VCO is locked to > the 12th multiple of the ICOM. This means the > output of the GE PLL exciter will have the stability > of the ICOM, times 12, period. > > Kevin Custer > > Wade Lake wrote: > > I stand corrected, in part anyway. In this > GE radio the deviation is indeed at a divide by 12 > from the output. This is why I said "usually", I am > not familiar with the intricate details of all > radios. Especially GE's, I was a Motorola tech for > quite a few years. I will leave the GE's to others > like you who are more familiar with their inner > workings. > > However, even in this particular radio, I > noticed the PLL circuit uses a X3 from the original > ICOM freq as the PLL reference. This is made > obvious by the divide by 4 fed back from the output > of the VCO. So even though the PLL circuit here is > not more stable by a factor of 12, as I initially > stated, it theoretically should be more stable by a > factor of 4. This does not appy to deviation in > this case but it will most definately apply to > frequency drift. > > My 2 and a half cents worth. > > Wade - KR7K > > > ----- Original Message ----- > From: Kevin Custer > To: Repeater-Builder@yahoogroups.com > Sent: Sunday, December 19, 2004 11:04 AM > Subject: Re: [Repeater-Builder] GE Mastr II PLL > vs. Multiplier (crystal) exciter in duplex service. > > > Hi Wade, > > I'm sorry, but I have to disagree with your > stability theory on the GE Mastr II PLL high-band > exciter. If you refer to the PDF manual for the PLL > exciter: > > <http://www.repeater-builder.com/ge/lbi-library/lbi-30398n.pdf> > You will see under the "Description" the exciter > utilizes the 12th multiple of the FM ICOM to lock > the VCO on frequency. It goes into more detail > about this in the "Circuit Analysis" section of the > same manual. So, the FM ICOM's multiplication > certainly does factor into the stability of the PLL > exciter, and one can generalize it has the same > frequency stability as its multiplier counterpart. > In addition, the modulation of the PLL exciter is > produced in the crystal reference (FM ICOM) as well, > and is also multiplied up to the desired deviation. > Since the time constant of the Lead/Lag filter > allows for near instantaneous correction of the VCO, > changes in frequency at the audio rate are > superimposed onto the output frequency. > > Hope this helps... > Kevin Custer > > > Wade Lake wrote: > > Kevin Custer wrote: > > The advantage here is the same frequency stability > is achieved by the use of the quartz reference > > Actually, a PLL oscillator is much more stable > than a multiplied crystal oscillator. because with > a multiplied quartz oscillator, frequency drift and > frequency error (usually deviation as well) is > multiplied by 12, at least in the case of the High > band GE MASTR II. > > Not to dissagree with you Kevin, your answer is > good, I think you nailed it. I just wanted to point > out that stability is a very strong point of the > PLL. Since it operates on the desired frequency, no > frequency error/drift is multiplied. > > Wade - KR7K > > __________________________________ Do you Yahoo!? All your favorites on one personal page – Try My Yahoo! http://my.yahoo.com 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/
